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31 Cards in this Set

  • Front
  • Back
One of three blood culture bottles drawn from a patient with unexplained fevers reveals gram-positive cocci
growing in clusters. Which of the following tests would be most useful in determining whether this organism is a
part of the normal skin flora?

A. Bacitracin resistance

B. Catalase

C. Coagulase

D. Novobiocin resistance

E. Optochin resistance
The correct answer is C. Gram-positive cocci in clusters are staphylococci. Staphylococcus aureus is a common pathogen that should not be considered normal skin flora. Other staphylococci, especially Staphylococcus
epidermidis, may contaminate blood cultures and can be differentiated from Staphylococcus aureus by the
coagulase test. S. aureus is the only coagulase-positive staphylococcus.

Bacitracin sensitivity differentiates Streptococcus pyogenes from the other beta-hemolytic streptococci, which
are bacitracin resistant (choice A).

The catalase test (choice B) is used to differentiate streptococci from staphylococci. Staphylococci produce
catalase and can generate oxygen bubbles in hydrogen peroxide, whereas streptococci cannot.

Novobiocin resistance (choice D) differentiates the coagulase-negative staphylococci into S. epidermidis
(novobiocin sensitive) and S. saprophyticus (novobiocin resistant).

Optochin resistance (choice E) differentiates the major pathogenic alpha-hemolytic streptococci. S. pneumoniae
is optochin- and bile-sensitive whereas S. viridans is resistant to both optochin and bile.
A 4-month-old infant presents with failure to thrive, progressive muscular weakness, and poor head control. On
questioning, the mother states that she typically feeds the baby soy-based formula sweetened with honey. Which
of the following organisms is most likely to be responsible for the child's presentation?

A. Clostridium botulinum

B. Clostridium difficile

C. Clostridium perfringens

D. Clostridium tetani

E. Corynebacterium diphtheriae
The correct answer is A. The baby has infant botulism (floppy baby syndrome), which is due to germination of
Clostridium botulinum spores (found in honey) in the baby's gastrointestinal tract. Patients improve when honey
is removed from the diet. This disorder is most common in children under the age of six months; older children
and adults do not appear to be vulnerable to this form of botulism, but are susceptible to botulism caused by
ingestion of preformed toxin.

Clostridium difficile(choice B) causes pseudomembranous colitis, especially after antibiotic therapy.

Clostridium perfringens(choice C) causes gas gangrene and gastroenteritis, and it is not associated with
ingestion of honey.

Clostridium tetani (choice D) causes tetanus, and does not cause a food-borne illness in infants.

Corynebacterium diphtheriae(choice E) causes diphtheria in susceptible individuals.
A 35-year-old woman presents to her gynecologist with complaints of burning on urination for the past 2 days.
Dipstick test of her urine demonstrates marked positivity for leukocyte esterase, but no reactivity for nitrite. Urine
culture later grows out large numbers of organisms. Which of the following bacteria are most likely to be
responsible for this patient's infection?

A. Enterobacter sp.

B. Enterococcus faecalis

C. Escherichia coli

D. Klebsiella pneumoniae

E. Pseudomonas aeruginosa

The correct answer is B. The positive leukocyte esterase test indicates the presence of neutrophils in the urine,
suggesting a bacterial infection. The nitrite test exploits the fact that most Enterobacteria (gram-negative enteric
rods) are able to form nitrite from nitrate; thus, the nitrite test is used to diagnose urinary tract infections. One
limitation of this method is the fact that enterococci (gut streptococci) do not produce nitrite from nitrate, but can
nonetheless cause urinary tract infections. Enterococcal urinary tract infections are often nosocomial and
classically acquired in the intensive care unit, although they can occur in other settings.

Enterobacter sp. (choice A), Escherichia coli(choice C), Klebsiella pneumoniae(choice D), and Pseudomonas
aeruginosa(choice E) can cause urinary tract infections and would usually be picked up by the dipstick for
nitrites. False-negative results might still be seen with these organisms if the infection was light, the bladder had
been recently emptied prior to collection, and the urine was "new" and had not yet grown enough bacteria to
produce a positive result.
A 37-year-old woman presents with 3 days of progressive joint pain in her ankles, knees, and wrists. She recalls three similar episodes over the past several years. On examination, she has a temperature of 38.7 C, her blood pressure is 110/70 mm Hg, and her heart rate is 90/min. She has a diffuse petechial rash over her trunk and extensor surfaces. Her ankles and knees are swollen, red, and tender with decreased range of motion, and there is tenderness over the tendon sheaths of her hands and forearms. Blood cultures are negative. Aspiration of joint fluid reveals a white cell count of 22,000/mm3 with no visible organisms, but culture on chocolate agar is positive.
Which of the following is an attribute of the causative organism that allows it to produce recurrent infections?

A. It is an intracellular pathogen

B. It is resistant to ceftriaxone

C. It is resistant to complement-mediated lysis

D. Its capsule is not immunogenic

E. Its pili undergo antigenic and phase variation
The correct answer is E. This is a case of Neisseria gonorrhoeae arthritis. Patients are continuously susceptible to reinfection because of antigenic variation and phase variation of the pili.

N. gonorrhoeae is not an intracellular pathogen (choice A), although it may be found intracellularly in neutrophils after it has been phagocytized.

Ceftriaxone (choice B) is the drug of choice for N. gonorrhoeae.

Gonococci are especially susceptible to complement-mediated lysis, not resistant to it (choice C).

N. gonorrhoeae has an insignificant capsule that does not play a major role in the pathogenesis, but its capsule is immunogenic (compare with choice D). Streptococcus pyogenes is the best known example of a nonimmunogenic capsule, made of hyaluronic acid, but virtually all other capsules are immunogenic.
A Pap smear from a woman with chronic cervicitis shows cytoplasmic inclusions within epithelial cells. Fluorescent antibodies identify both these inclusions and "elementary bodies." The intracellular organisms causing the infection are unusual because they cannot synthesize which of the following?




D. Proteins

The correct answer is A. The disease is chlamydial cervicitis. This venereally transmitted infection is usually suspected after treatment for gonorrhea fails to relieve symptoms. However, a few cases are picked up when cytoplasmic inclusions composed of aggregates of chlamydia are identified on Pap smears. Confirmation can be made with fluorescent antibodies that pick up both the aggregates and individual bacteria known as "elementary bodies." The organisms are obligate intracellular parasites because they have lost the ability to synthesize ATP. Although some authors consider them to be "bacteria," others do not, since this is such a fundamental difference between the chlamydia and free living bacteria.

Failure to synthesize cholesterol (choice B) is not usually cited as a problem specific to any type of organism, although viruses are not able to do so without using host machinery.

Some viruses cannot synthesize DNA (choice C), but the disease in question is not caused by a virus.

Protein synthesis (choice D) by viruses requires host ribosomes.

Some viruses cannot synthesize RNA (choice E), but the disease in question is not caused by a virus
A patient with colorectal cancer develops septicemia complicated by endocarditis. You would expect the blood cultures to grow

A. Streptococcus agalactiae

B. Streptococcus bovis

C. Streptococcus pneumoniae

D. Streptococcus pyogenes

E. Streptococcus viridans
The correct answer is B.Streptococcus bovis is a Group D streptococcus. There is a significant association between S. bovis bacteremia and endocarditis with carcinoma of the colon and other colonic diseases. Every patient with S. bovis bacteremia should undergo gastrointestinal and cardiac evaluation. Up to 50% of patients with S. bovis bacteremia are reported to have underlying colonic malignancies. In another study, 25-50% of cases of S. bovis bacteremia were associated with endocarditis, especially in patients with preexisting valvular lesions.

Streptococcus agalactiae(choice A) is an important cause of maternal and neonatal bacteremia and neonatal meningitis. It is part of the normal flora of the gastrointestinal tract and the female genital tract.

Streptococcus pneumoniae(choice C) is a leading cause of community-acquired pneumonia, meningitis in adults, otitis media (especially in children), and sinusitis. Spontaneous peritonitis due to S. pneumoniae is reported in children with ascites from nephrotic syndrome. Asplenia predisposes patients to severe infections with S. pneumoniae and other encapsulated organisms. S. pneumoniae infections are also more frequent and unusually severe in patients with sickle cell anemia, multiple myeloma, alcoholism, and hypogammaglobulinemia.
S. pneumoniae is now the leading cause of invasive bacterial respiratory disease in patients with AIDS.

Streptococcus pyogenes(choice D) is the most common cause of bacterial pharyngitis. Complications include paratonsillar abscesses, otitis media, and sinusitis. Long-term sequelae include rheumatic fever and poststreptococcal glomerulonephritis. S. pyogenes is also responsible for many skin and soft tissue infections.
The organism also produces many toxins that produce a variety of diseases.

Streptococcus viridans(choice E), or the viridans Streptococci, are the most common cause of subacute bacterial endocarditis, which should be suspected in cases of viridans streptococcal bacteremia. One species of viridans Streptococci, Streptococcus milleri, is frequently associated with pyogenic abscesses, especially of the liver.
A 54-year-old woman suffering from influenza deteriorates and develops shaking chills and a high fever. Physical
examination is remarkable for dullness to percussion at the left base and decreased breath sounds on the left.
Chest x-ray confirms the diagnosis of lobar pneumonia, presumed to be caused by Streptococcus pneumoniae.
The patient has no known drug allergies. Which of the following antibiotics would be most appropriate to treat the
patient's condition?

A. Cefotaxime



D. Penicillin

E. Vancomycin
The correct answer is D. Penicillin remains the first-line drug of choice for pneumococcal pneumonia, except in patients with penicillin allergy and in the relatively few areas in which pneumococcal strains with high-level penicillin resistance exist. Alternative therapies include erythromycin and vancomycin.

The third-generation cephalosporin cefotaxime (choice A) is not usually used for pneumococcal pneumonia.

Chloramphenicol (choice B) is not usually used for pneumococcal pneumonia.

Erythromycin (choice C) is a good alternative therapy for pneumococcal pneumonia, but is usually used only when a penicillin allergy is present.

Vancomycin (choice E) is not the first-line therapy, but it is a good alternative in patients allergic to penicillin or when high-level penicillin resistance (relatively uncommon) is present.
An otherwise healthy 3-year-old child is brought to the pediatrician with umbilicated, flesh-colored papules on his
trunk. This condition is related to infection with which of the following viruses?


B.Herpesvirus 6

C. Parvovirus

D. Poxvirus

E. Variola
The correct answer is D. The lesions are characteristic of molluscum contagiosum, which is a typically benign and self-limited condition caused by a poxvirus. The disease can be transmitted either venereally or through non-venereal contact. The other viruses listed do not cause similar skin lesions. Patients with advanced HIV infection may develop a severe, generalized, and persistent eruption, often involving the face and upper body.

Cytomegalovirus (choice A) causes congenital infections and disseminated infections in immunosuppressed patients.

Herpesvirus 6 (choice B)causes roseola (exanthem subitum).

Parvovirus (choice C) causes aplastic crises in patients with hemolytic anemia.

Variola (choice E) is the smallpox virus
A 39-year-old black man presents with complaints of anorexia, malaise, fatigue, dark urine, and upper abdominal discomfort. He admits to homosexuality, but denies blood transfusions, alcohol intake, or intravenous drug abuse. On physical examination, the patient has a temperature of 100.2 degrees F, scleral icterus, and jaundice.
His liver is palpable below the right costal margin, and there is moderate right upper quadrant tenderness. Liver function test results are as follows: total bilirubin 12.4%, SGOT 980 units, SGPT 1200 units. Serologic findings are as follows: anti-hepatitis A IgM negative, HBsAg positive, anti-HBc IgM positive, HBeAg positive, anti-HBsAb negative, hepatitis C negative. When this patient enters the window period, what would likely be the first change in his serologic findings?

A. He will become HBcAg positive

B. He will become HBc IgG positive

C. He will become HBeAg negative

D. He will become HBsAb positive

E. He will become HBsAg negative
The correct answer is E. This patient has acute hepatitis B. The "window period" refers to that period in infection when neither hepatitis B surface antigen (HBsAg) nor its antibody (HBsAb) can be detected in the serum of the patient. It is an immunologically mediated phenomenon caused by the precipitation of antigen-antibody complexes in their zone of equivalent concentrations and, thereby, their removal from the circulation. Because of this, the first thing that will happen in the window period is that the serum will become negative for the surface antigen (HBsAg), as that antigen is precipitated out of the serum by developing levels of its specific antibody (HBsAb).

HBcAg is not typically measured (choice A) in the serum.

Levels of the c-core antibody HBc IgG (choice B) and HBeAg (choice C) do not have a relationship to the window period.

Levels of HBsAb (choice D) will not be detectable until there is antibody excess, and the patient is leaving the window period
A 15-year-old girl in a rural community has swollen, painful lymph nodes in her right axilla. Physical examination
reveals multiple scratches on her right arm with a papule associated with one of the scratch marks. She states
that the scratches occurred about 5 days ago. What type of animal is the most likely source of the infection?

A. Cat or kitten

B. Chicken

C. Dog or puppy

D. Horse

E. Parrot
The correct answer is A. This patient has the classic symptoms of cat scratch disease caused by the bacillus
Bartonella henselae. The disease is self-limited with the onset of symptoms occurring 3-10 days following an
inoculating scratch. The organism can be isolated from kittens, typically less than 1 year of age, or from fleas. A
history of a new kitten in the house and the papule at the site of a scratch with regional painful adenopathy
defines the classic scenario.

Chickens (choice B) can harbor Salmonella spp. producing a gastroenteritis or enterocolitis. Chicken guano is
also a favorable environment for the fungus Histoplasma capsulatum. The mycelial phase thrives in the rich soil.
The human disease is a granulomatous infection involving the lungs and mimicking tuberculosis.

Dogs or puppies (choice C) carry Capnocytophaga canimorsus as part of the normal flora of the oral cavity.
Infections from licking or biting range from a self-limited cellulitis to fatal septicemia. Patients at risk for more
severe infections are those with asplenia, alcoholism, or hematologic malignancies. This organism is also
associated with cat bites, but the patient develops cellulitis and fulminant septicemia, especially in asplenic patients. Pasteurella multocida is another pathogen that colonizes the nasopharynx and gastrointestinal tract of cats and dogs. Cats have the highest rate of colonization (50-90%), followed by dogs (50%), swine (50%), and rats (14%). P. multocida most commonly causes a localized soft tissue infection or cellulitis after an animal bite,but systemic symptoms may be present in about 40% of the cases. These symptoms include osteomyelitis,septic arthritis, or tenosynovitis.

Horses (choice D) and horse manure have been associated with a pulmonary opportunistic infection with cavitation caused by Rhodococcus equi that resembles tuberculosis in immunocompromised patients.
Burkholderia mallei (the cause of glanders) is characterized by non-caseating granulomatous abscesses of skin, lymphadenopathy, and pronounced involvement of the lungs.

Parrots (choice E) are associated with psittacosis caused by Chlamydia psittaci. Psittacosis is associated with a dry, hacking cough productive of scant sputum, an interstitial infiltrate in the lungs, severe headache, and myalgias. A pale macular rash is also seen.
A 73-year-old woman with a history of diabetes presents with left ear pain and drainage of pus from the ear canal. She has swelling and tenderness over the left mastoid bone. Which of the following microorganisms is the most likely causative agent?

A. Hemophilus influenzae

B. Klebsiella pneumoniae

C. Mucor sp.

D. Pseudomonas aeruginosa

E. Streptococcus pyogenes
The correct answer is D.Pseudomonas aeruginosa causes malignant otitis externa, which is a severe necrotizing infection of the external ear canal. Infection tends to spread to the mastoid bone, temporal bone,sigmoid sinus, base of the skull, meninges, and brain. Patients at increased risk include the elderly, those with diabetes, and the immunocompromised. Pseudomonas is also associated with many other clinical syndromes,including infection following traumatic wounds to the feet in persons wearing sneakers or rubber-soled shoes, since the organism can be cultured from the shoes.

Hemophilus influenzae(choice A) produces a variety of clinical syndromes. H.Influenzae is the third-most
common cause of meningitis in children aged 1 month to 18 years. It is the most common cause of acute epiglottitis, the most common cause of purulent bacterial conjunctivitis, and the second-most common cause of otitis media. Patients at risk include those with COPD and cystic fibrosis, alcoholics, splenectomized patients, and young patients.

Klebsiella pneumoniae(choice B) is a gram-negative organism that produces a necrotizing pneumonia in
diabetics and alcoholics. Patients typically present with an abrupt onset of fever, shaking chills, and purulent,foul-smelling sputum.

Mucor (choice C) is a fungal infection that is particularly severe in the diabetic or the immunocompromised patient. In the acidotic diabetic, the fungus produces a life-threatening, invasive rhinocerebral infection. The infection begins in the nasal passages, extends into the paranasal sinuses, and spreads through the cribiform plate to the frontal lobes of the brain. Patients typically complain of headache, facial pain, and orbital swelling.

Streptococcus pyogenes(choice E) causes bacterial pharyngitis, otitis media, and sinusitis. It is also associated with toxin-related diseases and skin infections.
A 29-year-old female diagnosed with AIDS has been suffering from a progressive blurring of vision in her right
eye. On funduscopic examination, a small white opaque lesion is noted on the retina of her right eye. Which of
the following is the most appropriate therapy for this patient?

A. Acyclovir

B. Amantadine



E. Zidovudine
The correct choice is D. This patient is most likely suffering from cytomegalovirus (CMV) retinitis. The best drug treatment for this infection is ganciclovir.

Acyclovir (choice A) is not effective in CMV infections. It is used more for HSV type 1 and 2 infections.

Amantadine (choice B) is used either therapeutically or prophylactically for the influenza A virus.

Flucytosine (choice C) is an antifungal agent.

Zidovudine (choice E) is a first-line drug for the treatment of AIDS. The drug by itself is ineffective against CMV retinitis.
A newborn is infected in utero with an enveloped virus containing double-stranded DNA. The child develops
petechiae, hepatosplenomegaly, and jaundice. Brain calcifications are detected on computed tomography (CT).
With which of the following viruses is the newborn most likely infected?


B. Hepatitis B

C. Hepatitis C

D. Hepatitis D

E. Herpes simplex
The correct answer is A. The most common agents causing congenital infection in the United States are cytomegalovirus, herpes simplex virus, and Treponema pallidum. Congenital cytomegalovirus infection, which occurs in 1 to 2% of all live births in the U.S., results from transplacental acquisition of a primary or recurrent maternal infection. Most infections are asymptomatic, but about 5% will present with hepatosplenomegaly,periventricular brain calcification, petechial hemorrhages, and hydrops. Sensorineural deafness is a common manifestation in affected infants. Primary infection of the mother is strongly associated with more severe symptoms in affected infants. The mortality rate is 30% and most of the survivors will have neurologic impairment. CMV infections in children and adults are often asymptomatic; however, the virus is responsible for 10% of infectious mononucleosis cases (characterized by an absence of sheep RBC agglutinins). CMV also causes serious disease in immunosuppressed patients, including bone marrow recipients and AIDS patients.
Ganciclovir is the drug of choice, although foscarnet has also been used with some success.

Infections with hepatitis viruses (choices B, C, and D), if symptomatic, are characterized by jaundice, lethargy,failure to thrive, abdominal distention, clay- colored stools, and elevated transaminase levels. Hepatitis B(choice B) is the only viral hepatitis agent that is recognized as an important cause of neonatal disease. The infection is usually acquired during the birth process; therapy includes hyperimmune human anti-hepatitis B serum followed a few weeks later with active immunization with rHBsAg injections.

Herpes simplex (choice E) can also infect the neonate. The hallmark of infection is painful skin vesicles (present in 50% of affected infants); other manifestations include encephalitis, pneumonia, hepatitis, and disseminated intravascular coagulopathy. Massive hepatic and adrenal necrosis is common. Therapy is with acyclovir.
A 60-year-old alcoholic smoker abruptly develops high fever, shakes, a severe headache, and muscle pain. He initially has a dry, insignificant cough, but over the next few days he develops marked shortness of breath requiring assisted ventilation. Chest x-ray demonstrates homogeneous radiographic shadowing that initially involves the left lower lobe but continues to spread until both lungs are extensively involved. Culture of bronchoalveolar lavage fluid on buffered charcoal yeast extract (BCYE) demonstrates a coccobacillary pathogen.
Which of the following is the most likely causative organism?

A. Legionella pneumophila

B. Listeria monocytogenes

C. Spirillium minus

D. Staphylococcus aureus

E. Streptococcus pneumoniae
The correct answer is A. The patient has a severe, potentially fatal, pneumonia with prominent systemic symptoms. Culture on BCYE is the specific clue that the organism is Legionella pneumophila. The disease is
respiratory Legionellosis, also known as Legionnaire's disease, because the disease was first described when it
occurred in epidemic form following an American Legion convention at a Philadelphia hotel. Patients tend to be older (40-70 years old) and may have risk factors including cigarette use, alcoholism, diabetes, chronic illness,or immunosuppressive therapy.

Listeria monocytogenes(choice B) causes listeriosis and is not a notable cause of pneumonia.

Spirillium minus (choice C) is a cause of rat-bite fever and is not a notable cause of pneumonia.

Staphylococcus aureus(choice D) can cause pneumonia, but is easily cultured on routine media.

Streptococcus pneumoniae(choice E) can cause pneumonia, but is easily cultured on routine media.
A 33-year-old woman presents with fever, vomiting, severe irritative voiding symptoms, and pronounced costovertebral angle tenderness. Laboratory evaluation reveals leukocytosis with a left shift; blood cultures indicate bacteremia. Urinalysis shows pyuria, mild hematuria, and gram-negative bacteria. Which of the following drugs would best treat this patient's infection?

A. Ampicillin and gentamicin

B. Erythromycin

C. Gentamicin and vancomycin

D. Phenazopyridine and nitrofurantoin

E. Tetracycline
The correct answer is A. Acute pyelonephritis is an infectious disease involving the kidney parenchyma and the renal pelvis. Gram-negative bacteria, such as Escherichia coli, Proteus, Klebsiella, and Enterobacter, are the most common causative organisms in acute pyelonephritis. Laboratory evaluation will often reveal leukocytosis with a left shift, and urinalysis typically shows pyuria, varying degrees of hematuria, and white cell casts. Since bacteremia is present, the patient should be hospitalized and empirically started on IV ampicillin and gentamicin.
This regimen may be need to be changed, however, once the sensitivity results are available.

Erythromycin (choice B) and tetracycline (choice E) are both bacteriostatic antibiotics and would not be
recommended in a patient with a severe infection, such as acute pyelonephritis with bacteremia.

Vancomycin (choice C) is primarily used in the treatment of severe gram-positive infections.

Phenazopyridine (choice D) is a urinary analgesic, and nitrofurantoin (choice D) is a urinary tract anti-infective.
Although nitrofurantoin is indicated for the treatment of "mild" cases of pyelonephritis, as well as cystitis, this patient's condition is severe and should be treated with appropriate antibiotics.
A newborn infant has multiple, hemorrhagic, cutaneous lesions and does not respond to sound. Head CT scan shows periventricular calcifications. Which of the following infectious agents is the most likely cause of this childs presentation?

A. Cytomegalovirus

B. Herpes simplex

C. Rubella

D. Syphilis

E. Toxoplasmosis
The correct answer is A. The infectious agents listed are all important causes of congenital disease. The triad of
cutaneous hemorrhages ("blueberry muffin baby"), deafness, and periventricular CNS calcifications suggests congenital CMV infection, the most common cause of intrauterine fetal viral infection. Other manifestations include microcephaly and hepatosplenomegaly.

Neonatal herpes (choice B) may be congenital, but more commonly is acquired during vaginal delivery infection is characterized by vesicles on the skin and mucous membranes, encephalitis, or disseminated disease.

Congenital rubella (choice C) can cause mental retardation, heart abnormalities, blindness, encephalitis, and motor abnormalities.

Congenital syphilis (choice D) can cause death in utero, or a variety of problems including abnormal teeth, bones, and central nervous system.

Toxoplasmosis (choice E) can be either acquired during delivery (mild) or congenital (severe). Severe infections can cause stillbirth, chorioretinitis, intracerebral calcifications, and hydro- or microcephaly.
A very ill neonate has widespread granulomas. In utero infection with which of the following organisms is suggested by this finding?

A. Clostridium botulinum

B. Escherichia coli

C. Haemophilus influenzae

D. Listeria monocytogenes

E. Neisseria gonorrhoeae
The correct answer is D. All of the organisms listed can cause infection in infants, but Listeria monocytogenes is the one to cause potentially fatal granulomas (granulomatis infantiseptica) following in utero infection.

Clostridium botulinum(choice A) can cause infant botulism, characterized by failure to thrive, and progressive muscular weakness.

Escherichia coli(choice B) can cause diarrhea, pneumonia, and meningitis in infants.

Haemophilus influenzae(choice C) can cause acute epiglottitis, meningitis, pneumonia, and otitis media in young children.

Neisseria gonorrhoeae(choice E) can be transmitted via the birth canal, and causes ophthalmia neonatorum.
A 37-year-old female presents to the emergency room with a fever. Chest x-ray shows multiple patchy infiltrates
in both lungs. Echocardiography and blood cultures suggest a diagnosis of acute bacterial endocarditis limited to the tricuspid valve. Which of the following is the most probable etiology?

A. Congenital heart disease

B. Illicit drug use

C. Rheumatic fever

D. Rheumatoid arthritis

E. Systemic lupus erythematosus
The correct answer is B. The most probable etiology of bacterial endocarditis involving the tricuspid valve is illicit intravenous drug use, which can introduce skin organisms into the venous system that then attack the tricuspid valve. Staphylococcus aureus accounts for between 60% and 90% of cases of endocarditis in intravenous drug users.

The endocarditis associated with congenital heart disease (choice A) typically involves either damaged valves or atrial or ventricular septal defects. The tricuspid valve is not particularly vulnerable.

Rheumatic fever (choice C) most commonly damages the mitral and aortic valves, and tricuspid damage is usually less severe and seen only when the mitral and aortic valves are heavily involved. Consequently, secondary bacterial endocarditis involving only the tricuspid valve in a patient with a history of rheumatic fever would be unusual.

Rheumatoid arthritis (choice D) is not associated with bacterial endocarditis.

Systemic lupus erythematosus (choice E) can produce small, aseptic vegetations on valves, but is not associated with bacterial endocarditis.
A 4-year-old boy is brought to the emergency room in extreme respiratory distress, with a temperature of 103.8 degrees Fahrenheit. He is drooling and has difficulty swallowing, and on physical examination, inspiratory stridor is noted. A lateral x-ray shows swelling of the epiglottis. He has had no previous vaccinations. Which of the following agents is the most likely cause of these symptoms?

A. Haemophilus influenzae

B. Klebsiella pneumoniae

C. Legionella pneumophila

D. Mycoplasma pneumoniae

E. Streptococcus pyogenes
The correct answer is A. Epiglottitis is the most common disease of the upper respiratory tract produced by Haemophilus influenzae type b, a gram-negative encapsulated rod. It is also a common cause of otitis media in children and may cause bronchitis, bronchiolitis, and pneumonia in adults. The incidence of serious disease caused by Haemophilus influenzae type b has decreased greatly with the introduction of an effective vaccine.
The vaccine is composed of the H. influenzae type b capsular polysaccharides coupled to a carrier molecule, given to children between 2 and 15 months of age. The patient had not received the Hib conjugate vaccine and therefore was susceptible to this organism.

Klebsiella pneumoniae(choice B) causes pneumonia and pulmonary abscesses, but is not considered to be a pathogen in the upper respiratory tract.

Legionella pneumophila(choice C) causes pneumonia in man. The disease may be mild (an atypical pneumonia) or a fulminating disease with a high mortality (30%).

Mycoplasma pneumoniae(choice D) causes community-acquired atypical pneumonia. It is the most common cause of pneumonia in young adults.

Streptococcus pyogenes(choice E) is the most common cause of pharyngitis; however, this patient's presentation strongly suggests epiglottitis.
A 15-year-old boy presents to his physician with several weeks of slowly worsening pruritus of both of his feet. He is otherwise well and taking no medications. On examination, he has bilateral, erythematous, dry scaling lesions that are most obvious in the interdigital web spaces and on the soles. There is no bleeding or exudate. What would most likely be found in a potassium hydroxide (KOH) mount of a scraping of the affected skin?

A. Branching hyphae with rosettes of conidia

B. Branching, septate hyphae

C. Budding yeasts

D. Hyphae, arthroconidia, and blastoconidia

E. Pigmented, septate hyphal fragments

F. Short, curved hyphae and round yeasts
The correct answer is B. This is a case of tinea pedis, or athlete's foot, caused by a variety of dermatophytic
fungi, which are easily detected on alkali mounts of scraped skin as colorless, branching hyphae with cross-walls.

Hyphae with rosettes of conidia (choice A) describes the environmental/transmission form for Sporothrix schenckii, the agent of rose gardener's disease, which is a subcutaneous mycosis.

Budding yeasts (choice C) describes the form found in clinical specimens from patients with sporotrichosis.

Hyphae, arthroconidia, and blastoconidia (choice D) would be found in clinical specimens from patients infected with Trichosporon beigelii (white piedra), which is a superficial mycosis of the hair of the head.

Pigmented, septate hyphal fragments (choice E) would be found in cases of phaeohyphomycosis, a diverse group of cyst-forming subcutaneous, pigmented (dematiaceous) fungi, rare in the U.S.

Short, curved hyphae and round yeasts (choice F), or the "spaghetti and meatball" presentation in clinical specimens, are characteristic of Malassezia furfur, the agent of pityriasis versicolor.
A 24-year-old AIDS patient develops chronic abdominal pain, low-grade fever, diarrhea, and malabsorption.
Oocysts are demonstrated in the stool. Which of the following organisms is most likely to be the cause of the patient's diarrhea?

A. Diphyllobothrium latum

B. Entamoeba histolytica

C. Giardia lamblia

D. Isospora belli

E. Microsporidia
The correct answer is D. All of the organisms listed are protozoa. There are two intestinal protozoa specifically associated with AIDS that can cause transient diarrhea in immunocompetent individuals but can cause
debilitating, and potentially life-threatening chronic diarrhea in AIDS patients. These organisms are Isospora belli, treated with trimethoprim-sulfamethoxazole (or other folate antagonists) and Cryptosporidium parvum (no
treatment presently available).

Diphyllobothrium latum(choice A) is the fish tapeworm and occasionally causes diarrhea.

Entamoeba histolytica(choice B) and Giardia lamblia(choice C) are both causes of diarrhea, but they are not specifically associated with AIDS.

Microsporidia (choice E) are a protozoan cause of diarrhea, but produce spores rather than oocysts.
An African child develops massive unilateral enlargement of his lower face in the vicinity of the mandible. Biopsy demonstrates sheets of medium-sized blast cells with admixed larger macrophages. This type of tumor has been associated with which of the following?

A. Epstein-Barr virus and t(8;14)

B. Hepatitis B and t(9;22)

C. Herpesvirus and CD5

D. Human immunodeficiency virus and CD4

E. Human papillomavirus and t(2;5)
The correct answer is A. The patient has Burkitt's lymphoma. This type of lymphoma is a high-grade B-cell lymphoma that occurs in endemic form in Africa (it is the most common neoplasm in children in an equatorial belt that includes Africa and New Guinea) and sporadically in the United States and Europe. The sporadic form
is often in an abdominal site and occurs in young adults. The African form of Burkitt's lymphoma has been strongly associated with antibodies directed against Epstein-Barr virus; the association is weaker in sporadic cases. A characteristic translocation, t(8;14) (q24.l3;q32.33) has been described.

Hepatitis B (choice B) is associated with hepatocellular carcinoma. t(9;22) is the Philadelphia chromosome,which is seen in some cases of CML and AML.

Herpesvirus (choice C) does not have a strong tumor association, although a link to cervical cancer has intermittently been proposed. CD5 is a marker seen in small lymphocytic and mantle cell lymphomas.

HIV (choice D) is linked to Kaposi's sarcoma (and AIDS). Some patients also develop primary lymphomas (not usually Burkitt's). CD4 is a marker for helper T cells and some T cell lymphomas.

Human papillomavirus (choice E) is linked with common warts, genital condylomata, and genital cancers. t(2;5) is linked to anaplastic large cell lymphoma.
A 49-year-old Vietnamese man is diagnosed with tuberculosis. On physical examination, large flocculent masses are noted over the lateral lumbar back, and a similar mass is located in the ipsilateral groin. This pattern of involvement strongly suggests an abscess tracking along the

A. adductor longus

B. gluteus maximus

C. gluteus minimus

D. piriformis

E. psoas major
The correct answer is E. This is the classic presentation of a psoas abscess. This clinical entity was formerly a fairly common complication of vertebral tuberculosis, but is now rare in clinical practice in this country. The
psoas muscle is covered by a fibrous sheath known as the psoas fascia. This sheath is open superiorly,permitting an infection involving the soft tissues around the spine to enter the sheath, then track down to the groin.

The adductor longus (choice A) is a muscle of the anterior thigh, and is not related to the lumbar portion of the back.

The gluteus maximus (choice B) gluteus minimus (choice C) and piriformis (choice D) are muscles of the
buttock with no relationship to the groin.
A 36-year-old man with AIDS develops right-sided weakness involving the lower, but not the upper, limb. MRI scans reveal a ring-enhancing lesion within the white matter of the left frontal lobe. A biopsy shows coagulative necrosis of brain parenchyma with macrophage-rich chronic inflammatory infiltration admixed with microscopic cysts that contain characteristic bradyzoites. Which of the following is the most common source of this type of infection?

A. Anopheles mosquitoes

B. Bird droppings

C. Cats

D. Cooling systems

E. Washbasins
The correct answer is C. Clues to the correct answer are the underlying disease (AIDS), which predisposes
to opportunistic infections, the typical MRI appearance of the lesion (ring-enhancing mass), and the
histopathologic features (presence of encysted bradyzoites). In short, this patient has cerebral toxoplasmosis, which represents one of the most common opportunistic infections in AIDS. Toxoplasma gondii is a protozoon that infects humans who ingest the oocysts from cat feces or incompletely cooked lamb or pork. Only immunodepressed patients and fetuses are vulnerable to this infection. In the fetus, toxoplasmosis causes extensive damage to brain parenchyma and retina. Toxoplasmosis associated with AIDS manifests with necrotizing lesions surrounded by chronic inflammation. A ring-enhancing lesion is a mass that contains a rim of contrast enhancement (bright signal on MRI) surrounding a dark core corresponding to central necrosis. In AIDS, the most frequent causes of a ring-enhancing lesion are primary brain lymphoma and toxoplasmosis.

Anopheles mosquitoes (choice A) transmit malaria parasites. Cerebral malaria is caused by Plasmodium falciparum, which is able to adhere to endothelial cells of small cerebral vessels. Vascular occlusion ensues resulting in numerous small infarcts.

Bird droppings (choice B) represent the vehicle of infection for two of the most common opportunistic fungal infections affecting immunocompromised patients: cryptococcosis and histoplasmosis. Cryptococcus neoformans causes meningoencephalitis, not intracerebral necrotic lesions. Histoplasma capsulatum rarely affects the brain. These fungi can be visualized in tissue sections by silver stains.

Cooling systems (choice D) may harbor Legionella pneumophila, spreading the bacteria in aerosolized form. L.pneumoniae is a gram-negative bacterium that causes Legionnaire's disease, a fatal form of pneumonia that
first struck participants at a meeting of the American Legion. It has been reported in immunocompromised patients as well.

Washbasins (choice E) frequently contain Pseudomonas aeruginosa, which has also been isolated from
respirator devices, cribs, and antiseptic-containing bottles. P. aeruginosa tends to affect patients with cystic fibrosis, severe burns, or immune impairment. It may cause bronchopneumonia, osteomyelitis, endocarditis,
external otitis, and keratitis, but not cerebral infection.
A 28-year-old male intravenous drug user presents with a febrile illness that has lasted 2 weeks. He also complains of chills, weakness, dyspnea, cough, arthralgia, diarrhea, and abdominal pain. On examination, a heart murmur is present, and small, tender nodules are found on the finger and toe pads, along with small hemorrhages on the palms and soles. Three sets of blood cultures are obtained from different veins. While awaiting laboratory confirmation, an empiric antibiotic regimen should primarily be directed at which of the following organisms?

A. Enterococci

B. Pseudomonas aeruginosa

C. Staphylococcus aureus

D. Streptococcus pneumoniae

E. Streptococcus pyrogenes
The correct answer is C. This patient is presenting with signs and symptoms of acute infective endocarditis (IE).
The fact that the patient is an intravenous drug user places him at a very high risk for the development of IE.
The factors that determine the clinical presentation of IE include the nature of the organism, the valve infected,and the route of the infection. Although the clinical characteristics of IE can vary, most patients present with a febrile illness lasting several days to 2 weeks. This illness is often accompanied by a variety of nonspecific signs and symptoms such as chills, weakness, dyspnea, cough, arthralgia, diarrhea, and abdominal pain. Heart murmurs occur in approximately 90% of all patients, but may be absent in patients with right-sided infections.
Other clinical signs include Osler nodules (purplish or erythematous subcutaneous papules or nodules on the pads of the fingers and toes), Janeway lesions (hemorrhagic painless plaques on the palms and soles),
petechiae (small erythematous painless hemorrhagic lesions that may appear anywhere), and splinter hemorrhages (thin linear hemorrhages found under the nail beds of fingers and toes). The diagnosis of IE is dependent on positive blood cultures and echocardiographic evidence of "valvular vegetation" and/or valvular
injury, with echocardiography the preferred method of diagnosis. A past medical history of intravenous drug
abuse contributes to the diagnosis. The initial treatment measures of IE should be aimed at the stabilization of cardiac and/or respiratory symptoms, if applicable. The second priority is obtaining three blood cultures from different veins. Once the blood cultures are obtained, empiric antibiotic therapy for Staphylococci, Streptococci,and Enterococci should be instituted. Since Staphylococcus aureus accounts for most cases of acute IE,empiric coverage should primarily be directed toward Staphylococcus aureus.

Enterococci(choice A) cause a minority of cases of native valve endocarditis, but are not usually involved in endocarditis associated with intravenous drug abuse.

Gram-negative organisms such as Pseudomonas aeruginosa(choice B) are rarely the cause of IE.

Streptococcus pneumoniae(choice D) and Streptococcus pyogenes(choice E) are not common causes of IE.
A 20-year-old female presents with a two day history of dysuria and increased urinary frequency. She states that she was recently married and was not sexually active prior to the marriage. Physical exam reveals a temperature
of 100.7 °F with normal vital signs. Gynecological exam reveals no evidence of discharge, vaginitis, or cervicitis.
Urinalysis reveals 14 white blood cells per high-powered field with many gram-negative rods. The most appropriate therapy would be

A. ampicillin

B. ceftriaxone

C. fluconazole

D. gentamicin

E. metronidazole
The correct answer is A. The patient's presentation is consistent with a simple urinary tract infection; there is a short history of dysuria, increased urinary frequency and the appearance of white blood cells and gram-negative rods in the urine. Urinary tract infections are common in women after they become sexually active. The infection is likely caused by urethral trauma during intercourse, which leads to bacterial contamination of the bladder. Since the majority of these infections are caused by Escherichia coli (a gram-negative rod), the most appropriate therapy would be ampicillin for around 10 days.

Ceftriaxone (choice B) is the treatment of choice for uncomplicated infections with N. gonorrhoeae, now that
most strains are resistant to penicillin. Intravenous ceftriaxone is a regimen reserved for the treatment of
life-threatening infections.

Fluconazole (choice C) is indicated for the treatment of vaginal candidiasis. Since there is no vaginal discharge and the patient has gram-negative rods in the urine, a diagnosis of vaginal candidiasis can be excluded.

Gentamicin (choice D) would be an inappropriate choice since the majority of urinary tract infections caused by gram negative rods are sensitive to ampicillin and the potential for toxicity secondary to gentamicin is great.

Metronidazole (choice E) is an antibiotic typically used in the treatment of Trichomoniasis, Giardiasis, and Gardnerella, as well as serious infections believed to be caused by anaerobic bacteria. Since there is no vaginal discharge and the patient has gram negative rods in the urine, one can conclude that these infections are not present and the patient instead has a urinary tract infection
A 36-year-old mother of two children presents with a 4-day history of swollen, painful hands. Her wrists and
metacarpophalangeal joints are boggy and inflamed bilaterally. Her 5-year-old son had been sent home from
school approximately 3 weeks previously with red cheeks and a blotchy rash on his torso. What is the most likely diagnosis?

A. Listeriosis

B. Lyme disease

C. Mumps

D. Parvovirus

E. Reiter's syndrome

The correct answer is D. Parvovirus B19 causes erythema infectiosum, or Fifth disease. The 5-year-old boy has the classic "slapped cheek" appearance. Adults typically do not get the facial rash, but have arthralgias and arthritis. The symmetrical distribution of involved joints is similar to that in rheumatoid arthritis. The onset in adults is typically 3 to 4 weeks after exposure. Parvovirus infections may persist in immunosuppressed patients,resulting in red blood cell aplasia.

Listeriosis (choice A) is caused by the gram-positive rod Listeria monocytogenes. Meningitis and bacteremia are common clinical manifestations. Elderly, neonates, pregnant women, and those taking steroids have the highest risk for infection.

Lyme disease (choice B) is caused by Borrelia burgdorferi. It is the most common vector-borne disease (Ixodes ticks) in the U.S. The incidence is highest in the summer and fall. The white-footed mouse and the white-tailed deer are zoonotic reservoirs. From 3 to 32 days following a tick bite, the patient develops fever, lymphadenopathy, meningismus, and the characteristic rash (erythema migrans). The rash enlarges and resolves over 3 to 4 weeks. Sequelae include arthritis, carditis, and neurologic abnormalities.

Mumps (choice C) is caused by a Paramyxovirus. The virus most commonly affects glandular tissue. Parotitis, pancreatitis, and orchitis are characteristic. Mumps meningoencephalitis is one of the most common viral meningitides. Mumps polyarthritis is most common in men between the ages of 20 and 30 years. Joint symptoms
begin 1 to 2 weeks after the parotitis subsides and large joints are involved.

Reiter's syndrome (choice E) is a seronegative, asymmetric arthropathy predominantly affecting the lower extremities. It may be triggered by a C. trachomatis infection. In addition to the arthritis, patients may have
urethritis (which is usually due to chlamydia), conjunctivitis, mucocutaneous disease such as balanitis, oral ulcerations, or keratoderma. Approximately 80% of patients are HLA-B27 positive.
A 28-year-old pregnant woman develops a flu-like illness with fever, headache, myalgia, and back pain. As a complication of the illness, she has a spontaneous abortion. Examination of the abortus demonstrates severe
amnionitis. Which of the following organisms would most likely be isolated from the placental membranes?

A. Borrelia burgdorferi

B. Leptospira interrogans

C. Listeria monocytogenes

D. Spirillium minus

E. Streptobacillus moniliformis
The correct answer is C. Spontaneous abortion is a problem associated with Listeriosis, caused by Listeria monocytogenes. The pattern of abortions was first recognized in herd animals, notably sheep and cattle, and then listeriosis was later implicated as a cause of spontaneous abortion in pregnant women. Listeriosis can occur in either epidemic (food-borne or hospital-acquired) forms or may be sporadic (noticed in animal or animal product handlers). Soft cheeses like Brie are a particularly common source of food-borne listeriosis. The disease may range in severity from asymptomatic carrier cases, to flu-like illness, to spontaneous abortion or neonatal death, to fatal illness in children or adults secondary to septicemia or meningoencephalitis. Other localized infections can also occur, primarily in the immunosuppressed. The treatment of choice is intravenous administration of ampicillin or penicillin, often in combination with an aminoglycoside.
Trimethoprim-sulfamethoxazole has been used successfully in patients with penicillin allergy.

Borrelia burgdorferi(choice A) causes Lyme disease.

Leptospira interrogans(choice B) causes leptospirosis.

Spirillium minus(choice D) is a cause of rat-bite fever.

Streptobacillus moniliformis(choice E) is a cause of rat-bite fever.
A 14-year-old boy has just moved with his family from Brazil to the U.S. He starts complaining of shortness of
breath and palpitations. Chest x-ray films demonstrate pulmonary congestion, and ECG shows alterations in heart rhythm. Echocardiography reveals biventricular dilatation with massive cardiac enlargement. An endomyocardial biopsy shows diffuse interstitial fibrosis, myocyte necrosis, chronic inflammation, and the
presence of intracellular protozoan parasites. The patient may also develop which of the following complications?

A. Achalasia

B. Chronic arthritis

C. Cysts in the brain

D. Pleuritis

E. Splenomegaly
The correct answer is A. The patient has myocarditis due to Trypanosoma cruzi. This infectious condition, known as Chagas disease, is endemic in vast areas of South America and is transmitted from person to person by triatomids known as "kissing bugs." Experts assess the number of persons with Chagas disease at about 7 million with about 35 million at risk in South America. T. cruzi is an intracellular protozoon that localizes mainly in the heart and nerve cells of the myenteric plexus, leading to myocarditis and dysmotility of hollow organs, such
the esophagus, colon, and ureter. Cardiac involvement manifests with ventricular dilatation and congestive
heart failure secondary to myocyte necrosis and fibrosis. Intracellular parasites can be visualized in tissue sections. Chagas disease is a cause of acquired achalasia, in which the distal third of the esophagus dilates because of loss of its intrinsic innervation. A similar pathologic mechanism accounts for megacolon and megaureter in Chagas disease.

The remaining choices refer to different infectious conditions that may also involve the myocardium:

Chronic arthritis (choice B) is a manifestation of the chronic stage of Lyme disease, which is caused by Borrelia burgdorferi and is transmitted to humans by deer ticks. Skin, CNS, and heart are the main targets of this infection.

Cysts in the brain (cysticerci) (choice C) may develop as a consequence of infestation by the tapeworm Taenia solium. Humans acquire this parasite by ingesting the eggs from undercooked pork. Cysticercosis may also
affect the heart, skeletal muscle, and skin.

Group B coxsackievirus infections cause pleuritis (choice D) and myocarditis, manifesting with fever, chest pain,
and, if myocarditis is severe, congestive heart failure. As in any form of viral myocarditis, the myocardium is infiltrated by lymphocytes, but there are no morphologic markers specific for Coxsackievirus infection.

Splenomegaly (choice E), often of massive proportions, is seen in patients with malaria. Plasmodium organisms can also invade the myocardium, leading to myocarditis.
A debilitated 72-year-old woman develops dry cough, fever, headache, and muscular pains. She treats herself with aspirin and ampicillin without any improvement. Her children take her to a local hospital, where chest x-ray films reveal scattered opacities, suggestive of interstitial infiltration. Laboratory investigations demonstrate the
presence of cold agglutinins. She is treated with erythromycin, and her symptoms rapidly improve. Which of the following is the most likely etiologic agent of this patient's condition?

A. Influenza virus

B. Mycoplasma pneumoniae

C. Pneumocystis carinii

D. Respiratory syncytial virus

E. Streptococcus pneumoniae
The correct answer is B. The patient's clinical presentation is typical of primary atypical pneumonia. In contrast to bacterial pneumonia, primary atypical pneumonia presents with the following features:

- Caused by M. pneumoniae; less frequently by viruses (influenza, respiratory syncytial virus, adenovirus,rhinoviruses, rubeola and varicella virus), Chlamydia, or Coxiella burnetii

- Characterized pathologically by interstitial, rather than intra-alveolar, inflammation

- Characterized clinically by nonspecific symptomatology and few "localizing" symptoms

Why is M. pneumoniae, and not influenza virus (choice A) or respiratory syncytial virus (choice D), the cause of this patient's pneumonia? First, M. pneumoniae infections are often associated with the appearance of cold agglutinins in the serum, detection of which is diagnostically important. Second, the patient responded quickly to treatment with erythromycin, an antibiotic effective against M. pneumoniae, but obviously not effective in treating viral infections.

Pneumocystis carinii(choice C) is a fungal organism causing pneumonia in severely immunocompromised hosts,especially AIDS patients. P. carinii pneumonia (PCP) is characterized by accumulation of a frothy exudate containing numerous organisms within alveolar spaces. Also, P. carinii is not sensitive to erythromycin. The drug of choice for treatment of PCP is trimethoprim-sulfamethoxazole.

Streptococcus pneumoniae(choice E) is the usual causative agent of lobar pneumonia, characterized by consolidation of a single lobe due to intra-alveolar acute inflammatory exudation. Lobar pneumonia is more prevalent in young, healthy individuals, whereas primary atypical pneumonia favors old, debilitated patients. S.pneumoniae is highly sensitive to penicillin.
A 25-year-old female presents with a confluent maculopapular rash that began on her face, then spread downward over her trunk. She states that 3 days ago she started having a fever and headache, with bilateral pain associated with the front and back of her neck. She also complains of joint pain. Which of the following diseases does she most likely have?

A. Infectious mononucleosis

B. Lyme disease

C. Roseola

D. Rubella

E. Rubeola
The correct answer is D. Rubella, also called German measles or 3-day measles, is a disease caused by a Togavirus, which are small, enveloped, single-stranded, (+) linear RNA viruses. Approximately 40% of patients are asymptomatic or have mild symptoms. In symptomatic patients, the clinical presentation typically consists of an erythematous rash beginning on the head, which spreads downward to involve the trunk, lasting for approximately 3 days. In addition to a transient rash, symptoms include fever, posterior cervical lymphadenopathy, and arthralgias. The greatest danger from rubella is to the fetus. If clinical rubella develops or seroconversion is demonstrated, there is a high risk of congenital abnormalities or spontaneous abortion.
The risk varies from 40%–60% if infection occurs during the first 2 months of gestation to 10% by the 4th month. Females of childbearing age should be warned not to become pregnant within 2-3 months from the time of immunization. Mild arthralgias and other symptoms may develop in 25% of immunized women. Enteroviral rashes may mimic rubella and rubeola.

Infectious mononucleosis (choice A) is caused by the Epstein-Barr virus, a herpesvirus. Classic findings include fever, exudative pharyngitis, generalized lymphadenopathy, severe malaise (most common complaint), and hepatosplenomegaly. A rash is not a characteristic feature unless the patient has been treated with ampicillin.

Lyme disease (choice B) is caused by the spirochete Borrelia burgdorferi. The disease is transmitted by the bite of the tick, Ixodes dammini. Reservoirs in nature include the white-tailed deer and the white-footed mouse. The initial lesion is an annular rash with central clearing and a raised red border (erythema chronicum migrans) at the bite site. The rash is warm, but not painful or itchy. Patients also have fever, malaise, myalgias, arthralgias,headache, generalized lymphadenopathy, and, occasionally, neurologic findings.

Roseola (choice C) is caused by human herpesvirus 6. Other names include exanthem subitum or sixth disease. Children have a febrile period of 3–5 days with rapid defervescence followed by an erythematous maculopapular rash lasting 1–3 days.

Rubeola (choice E), or regular measles, is a disease caused by a paramyxovirus. Patients present with an upper respiratory prodrome and characteristic oral lesions (Koplik's spots) that precede the rash. The non-pruritic maculopapular rash begins on the face and spreads to the trunk and extremities, including palms and soles. The incubation period is 10–14 days. Patients also have a posterior cervical lymphadenopathy. The virus is not associated with risk to a fetus.