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94 Cards in this Set
- Front
- Back
What are three G- rods associated with resporatory tract infections?
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1) Haemophilus influenzae
2) Legionella pneumophilia 3) Bordetella pertussis |
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What virulence factor do these organisms have in common?
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Lipopolysaccharide (LPS), which is common to all gram-negative bacteria.
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What are their oxygen requirements?
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Facultative anaerobes.
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What are the structure of Haemophilus?
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Pleomorphic; from coccobacillus to long slender rods
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Why can Haemophilus be difficult to visualize on Gram stain?
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The organisms are small
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What are two pathogenic species of Haemophilus?
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1) H. influenzae
2) H. ducreyi |
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How are serotypes of H. influenzae distinguished?
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By their capsular polysaccharide
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How many different serotypes exist?
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6
There is another type which is denoted "nontypable" because it is unencapsulated. |
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What is the natural host of H. influenzae?
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Humans are the only natural host
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Where is H. influenzae commonly found?
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Normal flora of the upper respiratory tract.
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How is H. influenzae transmitted?
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Respiratory droplets
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What virulence factors enable H. influenzae to attach to respiratory mucosa?
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IgA protease and several types of adhesins.
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What are two general types of infections caused by H. influenzae?
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1) Localized infections of the respiratory tract secondary to contiguous spread of bacteria (pneumonia)
2) Disseminated disease secondary to bacteremia (meningitis) |
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What part of H. influenzae enables it to cause disseminated disease?
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The capsule
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Do unencapsulated H. influenzae cause meningitis?
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NO
Unencapsulated bacteria cannot survive in teh bloodstream or cause disseminated disease. |
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Which serotype of H. influenzae is associated with severre infections?
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Type b
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Why is type b H. influenzae associated with severe infections?
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The capsule is composed of polyribose phosphate, facilitating tissue invasion.
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What are four major infections caused by H. influenzae in children?
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1) Sinusitis
2) Otitis media 3) Meningitis 4) Epiglottitis SOME is an acronym for the infection caused by H. influenzae in children |
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What makes epiglottitis a life-threatening disease?
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The swollen epiglottis may obstruct the airway.
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What major adult infection is caused by H. influenzae?
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Pneumonia
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What population has an increased risk of infection with H. influenzae?
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Patients with COPD who cannot effectively clear the organism.
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What are other clinical manifestations of H. influenzae?
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1) Septic arthritis
2) Purulent conjunctivitis 3) Brazilian purpuric fever |
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How is H. influenzae definitively diagnosed in the lab?
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Culture on chocolate agar
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Which two factors are required for growth of H. influenzae on laboratory media?
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Factor V (NAD)
Factor X (heme) |
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How can meningitis be diagnosed?
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1) Cerebrospinal fluid (CSF) Gram stain
2) Latex agglutination 3) Immunoelectrophoresis 4) Radioimmune assay of CSF |
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How are upper respiratory tract infections with H. influenzae treated?
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Antibiotics including TMP-SMX
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How are disseminated H. influenzae infections treated?
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Third-generation cephalosporins such as ceftriaxone or cefotaxime
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Why use third-generation cephalosporins for H. influenzae?
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Many of the type b organisms produce Beta-lactamase, which destroys penicillin and ampicillin
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What precent of H. influenzae type b isolates produce Beta-lactamase, thus requiring treatment with a cephalosporin?
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20-30%
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What is the mortality rate for untreated H. influenzae meningitis?
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90%
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How are H. influenzae infections prevented?
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Adminitration of childhood conjugate vaccine.
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What are the components of the conjugated H. influenzae vaccine?
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Type b capsular polysaccharide conjugated to diptheria toxoid or another carrier protein.
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Why is Type ba capsular polysaccharide conjugated to diphtheria toxoid in the H. influenzae vaccine?
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The toxoid is antigenic, increasing the immunogenic response to the vaccine.
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At what age is the H. influenzae administered?
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2-15 months
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How effective is the conjugated H. influenzae vaccine?
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It has reduced the incidence of meningitis in immunized children by 90%.
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How has the introduction of the H. influenzae vaccine affected teh prevalence of H. influenzae meningitis?
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Until introduction of the vaccine in the early 1990s, H. influenzae was the number one cause of miningitis in children.
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Which drug is used prophylactically for close contacts of H. influenzae-infected patients?
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Rifampin
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Why is Rifampin used prophylactically for H. influenzae contact?
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Rifampin is secreted in saliva and therefore reduces respiratory carriage of organisms.
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How is H. ducreyi transmitted?
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Sexually
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What does H. ducreyi cause?
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Chancroid on the genitals and inguinal lymphadenopathy (buboes)
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Who are H. ducreyi lesions distinguished from those of Treponema pallidum syphilitic lesions?
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H. ducreyi chancres are very painful and tend to have ragged edges, whereas T. pallidum chancres are shallow, indurated, painless ulcers.
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What is the sturcture of Legionella?
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Unencapsulated slender rods that may appear coccobacillary.
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How many different species of Legionella exist?
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34
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Which species is responsible for 90% of human disease caused by Legionella?
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Legionella pneumophilia
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What is the primary reservoir of Legionella?
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Environmental water sources that contain stagnant water such as air conditioners.
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How is Legionella transmitted?
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Inhalation of aerosolized organisms.
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Why is Legionella occasionally transmitted by swimming in pools?
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It is chlorine tolerant
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What type of immune response prevents Legionella infection?
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Innate immunity
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How does innate immunity prevent Legionella infection?
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Alveolar macrophages phagocytose bacteria, normally killing the organism.
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What allows Legionella to be pathogenic?
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Failure of fusion between the phagosome and lysosome allows bacteria to multiply with the protected environment of the phagosome until it ruptures, releasing bacteria.
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What two infections are caused by Legionella?
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1) Legionnaire's disease
2) Pontiac fever |
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What is Legionnaires' disease?
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An atypical pneumonia with a lobar distribution
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What percentage of patients exposed to Legionella develop Legionnaires' disease?
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1-5%
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Which populations are most susceptible to Legionella infection?
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Elderly,
Smokers Alcoholics Immune-suppressed individuals |
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What type of sputum is seen in Legionella pneumonia?
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Scant and nonpurulent
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What does Gram stain of sputum from a person with Legionella pneumonia demonstrate?
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Neutrophils without bacteria
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What nonrespiratory clinical findings accompany Legionella infection?
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Confusion
Fever Malaise Myalgias Anorexia Diarrhea Proteinuria Hematuria Death |
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What metabolic abnormality is commonly associated with Legionella pneumonia?
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Hyponatremia
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What is the fatality rate for Legionnaires' disease?
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5-30%
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What is Pontiac fever?
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An influenza-like illness
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How is Legionella diagnosed?
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1) Culture
2) Serology |
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Which method is the gold standard for diagnosis of Legionella?
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Culture
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What are the culture requirements for Legionella?
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Special medium containing buffered charcoal yeast extract with iron and L-cysteine.
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How is Legionella diagnosed by serology?
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Antibody titers or urine antigen detection.
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What role does Gram stain have in the diagnosis of Legionella?
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A minor one because Legionella stains poorly with Gram stain.
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What is the treatment for Legionella?
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Legionnaires' disease is treated with erythromycin or azithomycin and supportive therapy; Pontiac fever is treated symptomatically.
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What is the structure of Bordetella?
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Small, encapsulated coccobacillus that grows singly or in pairs.
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How are serotypes of Bordetella distinguished?
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Cell-surface molecules called agglutinogens.
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What does bortetella pertussis cause?
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Whooping cough
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How is B. pertussis transmitted?
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Respiratory droplets (highly contagious)
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What populaation is most susceptible to B. pertussis infection?
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Infants and children
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How does B. pertussis interact with the respiratory epithelium?
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Attaches to cilia without invading the tissue, producing toxins and virulence factors that eventually cause cilia to die.
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What is the major toxin produced by B. pertussis?
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Pertussis toxin
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What is the structure of pertussis toxin?
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Two subunits, including an enzymatically active A subunit and a B subunit that bind host cells.
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What is the function of the A subunit of B. pertussis?
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Stimulates adenylate cyclase resulting in increase camp by adenosine diphosphate (ADP) ribosylating (and therefore inactivating) Gi, the inhibitory subunit of the G protein.
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What makes pertussis toxin pathogenic?
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1) Lymphocytosis
2) Increased histamine sensitivity 3) Insulin secretion secondary to pancreatic Beta-islet cell activation resulting in hypoglycemia. |
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What are five other virulence factors produced by B. pertussis?
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1) Filamentous hemagglutinin
2) Adenylate cyclase toxin 3) Dermonecrotic toxin 4) Tracheal toxin (peptidoglycan) 5) Agglutinogens |
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What is the mechanism of Filamentous hemagglutinin in B. pertussis?
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Allows bacteria to attach to ciliated epithelial cells.
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What is the mechanism of Adenylate cyclase toxin of B. pertussis?
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Taken up by leukoctes, causing excessive accumulation of intracellular cyclic adenosine monophosphate (cAMP), resulting in decreased chemotaxis and phagocytosis of bacteria.
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What is the mechanism of Dermonecrotic toxin of B. pertussis?
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Vasoconstriction and ischemic necrosis.
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What is the mechanism of Tracheal cytotoxin of B. pertussis?
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Inhibits cillia movement and regeneration of damaged cells.
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What is the mechanism of Agglutinogens of B. pertussis?
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Facilitates attachment of bacteria to host cells.
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What part of the respiratory tract does B. pertussis infect?
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Tracheobronchioles.
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What is the incubation period for pertussis?
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1-3 weeks
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What are the three stages of whooping cough?
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1) Catarrhal phase
2) Paroxysmal phase 3) Convalescent phase |
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What are the symptoms of the catarrhal phase of pertussis?
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Nonspecific symptoms, including copious rhinorrhea, conjunctival infection, malaise, fever,and nonproductive cough.
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What are the symptoms of the paroxysmal phase fo pertussis?
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Paroxysmal, productive hacking cough which often ends with an inspiratory "whoop" and ma last up to 4 weeks.
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What are the symptoms of the convalescent phase?
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Less-frequent and less-severe coughing episodes with gradual resolution after 1-3 months.
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How is B. pertussis infection diagnosed?
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Clinical suspicion with marked lymphocytosis.
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How is pertussis confirmed?
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Culture of B. pertussis from nasopharynx of symptomatic patient or direct fluorescent antibody test.
Blood cultures will always be negative. |
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What type of medium is required for growth of B. pertussis?
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Selective agar medium containing blood and charcoal supplemented with antibiotics to inhibit growth of other normal flora of the nasopharynx.
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What is the treatment for B. pertussis?
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Erythromycin and supportive therapy.
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What two vaccines are available for B. pertussis?
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1) Acellular vaccine containing proteins from inactivated pertussis toxin
2) Killed whole cells |
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Which vaccine for B. pertussis is approved for use in the US?
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Acellular vaccine usually given with diptheria and tetanus toxoids in 3 doses beginning at 2 months of age.
(DTaP) |