Nosocomial Infections

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Nosocomial Infections

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infection developed while institutionalized - usually hospitals and long term care (nursing homes) facilities
> most common- dirty surgery- surgery that crosses or is continguous with a mucous membrane has a very high post-operative infection rate

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biofilms

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the introduction of plastics and other synthetic inert materials such arificial joints enable biofilms to grow.
Organisms growing on biofilms are most resistant to antimicrobial and the phagocytic clearance

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two types: endogenous and exogenous

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endogenous- arises from patient's normal flora (ex. oropharyngeal flora)

-exogenous- organisms found in hospital environment (ex. pseudomonas aureginosa)
--resistant to multiple antimicrobials: nthe concept of antimicrobial cycling has been developed to attampt to reduce the resistance of gram (-) hospital flora
--gram (-)
--sources
--> direct contact- (ex. S. aureus)
--> inhalation-pseudomonas auruginosa form venhilation
-->ingestion-food poisning
-->injection- contaminated IV fluids

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common sources of nosocomial infection

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-urinary tract infection
-surgical site infection
-repiratory
-bloodstream

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Pseudomonas aeruginosa

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-• produces distinctive blue-green pigment called pyocyanin.
-ubiquitious in nature
-virulence factors: adhesins, flagella, endotoxin, protease, lipases, and exotoxin A (inhibits protein synthesis)
-resistant to a wide variety of anitmicrobial agents

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Stapylococcus aureus

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-leading cause of nosocomial bacteremia, respiratory and wound infections @ UNC Hospitals in 2010
-virulence factors including coagulase, leukocidin, and hemolysins, and exotoxins.
-Some exotoxins such as TSST-1 (Toxic Shock Syndrome Toxin-1) can act as superantigens. S. aureus can colonize skin and nares; nasal carriage rate are estimated at 20 to 40% in adults.

• can survive on surfaces for long period of time
• can be spread by hands or from the environment
• control measures - barrier nursing, i.e., isolate patient, wear gloves and gowns, wash hands with antiseptic soap after patient contact.

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Oxacillin resistant Staphylococcus aureus (ORSA)

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-Resistance to oxacillin is due to modification in penicillin binding proteins; isolates are typically multi-drug resistant;


Two different clones seen on the hospital- CA-MRSA (becoming more common) is susceptible to oral agents and HCA-MRSA (still important and predominate)-highly drug resistant
• Causes more deaths in US than HIV
• MRSA have a higher mortality and length of hospitalization than MSSA
• Bloodstream infections with both CA- and HCA- MRSA are treated with vancomycin; 11 isolates of vancomycin resistant of S. aureus have been reported in the US- the gene for resistance is the vanA gene transferred from vancomycin resistant enterococci-no evidence of person-to-person spread-likely explained by poor “fitness” of VRSA
• A second resistant variant, “vancomycin intermediate S. aureus” or VISA is emerging; organism has thickened cell wall that is thought to protect from the activity of vancomycin-patients tend to be quite refractory to vancomycin therapy
-Spores can survive in the environment for months and are refractory to disinfectants. Alcohol gels do not kill these spores
-Disease is most severe and most common in those over 65 years

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Clostridium ¬difficile

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-Clostridium difficile is the most important cause of infectious diarrhea in the industrialized world
-The pathogenicity of this organism is due to its ability to produce two exotoxins, called Toxin A & B.
-Therapy is typically with metronidazole but recurrences of infection are an increasing problem.

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Clostridium ¬difficile pathogenicity

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Organism has the ability to cause disease due to production of two toxins
a. Toxin A or enterotoxin
b. Toxin B or cytotoxin
2. Strains of C. difficile typically produce either both toxins or neither; strains that produce only one toxin are highly unusual but do occur
3. Both C. difficile toxins have two subunits, a B or binding subunit and an A or biologically active subunit.
4. Pathogenesis/Clinical disease

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NAP 1/027 strain, an emerging “superbug”

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organism produces 20 times more toxin than typical strains because of mutation in the tcdC gene
>. strain has been found to cause disease in healthy children and adults with no or distant exposure to antimicrobials
>relapse or reoccurrences are much more common with this organism despite the organism retaining in vitro susceptibility against metronidazole

-Metronidazole p.o. recommended as treatment of choice

-THE SUPERBUG HAS TO TAKE A NAP ON THE METRO TO HELL (as in death!)