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Tufts OpenCourseware
Author: David R. Snydman
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1. Overview

Approximately 5 per cent of all patients develop a nosocomial infection as a result of being hospitalized, with an average resultant stay in-hospital of 13 days longer than controls. Costs nationally are 5 billion dollars.

1.1. Nosocomial Infection:

An infection acquired in hospital which was not present or incubating at admission.

Nosocomial infection (NI) incidence is related to severity of underlying disease, i.e. patients with a 50 per cent chance of death in 1 year have a 40 per cent chance of NI, whereas a patient with a non-fatal illness have only a 3 per cent chance of NI.

Sites of NI are found in the following frequency:

  • Urinary Tract 40 %
  • Surgical Wound 25 %
  • Respiratory Tract 20%
  • Bacteremia 3 %
  • Other 12%

2. Agents

Organisms that cause nosocomial infections are similar to community agents but there are exceptions:MRSA (Methicillin Resistant S. aureus), VRE (Vancomycin Resistant Enterococci), and ESBL (Extended Spectrum Beta Lactamase producing Klebsiella and E. Coli) have become more common.

3. Encounter

Organism transmission can occur from direct contact from hands, or indirect through air, fomites (environmental surfaces)!

Blood transfusions may be contaminated. Staff may be carriers of organisms, such as S. aureus or group A B-hemolytic streptococci.

Organisms in environment, like fungi, may be endemic, but due to nature of immunosuppression cause disease in some hosts (like BMT).

4. Entry

Organisms enter through barriers that have been breached, such as intravenous catheters, or invasive procedures.

4.1. Burn patients may be at risk for skin colonization and develop Pseudomonas sepsis.

4.2. Inhalation or aspiration pneumonia may occur following surgery and anesthesia.

4.3. Ingestion of C. difficile may lead to antibiotic associated diarrhea, or VRE may be ingested and lead to colonization which precedes invasive infection.

There are certain factors related to hospitalization that carry an undue risk of a nosocomial infection:Endotracheal Tube, Bladder Catheter, Intravenous Catheter, Non-Elective admission, age over 65 years, operative procedure during admission, hyperalimentation (TPN), immunosuppression.

5. Nosocomial Urinary Tract Infections

Usually related to GU manipulation and Foley catheterization, closed- catheter drainage has decreased the risk of bacteriuria but the risk is cumulative and is ~ 5% per day of placement. Risk of bacteriuria related to skill of person inserting Foley, and adequacy of Foley care (i.e. use of proper technique). Females > 50 have highest risk of infection.

5.1. Pathophysiology of infection:

The collection bag may become contaminated or organisms may traverse Foley-meatal interface, causative organisms are usually host flora--E. coli Enterococci, Proteus, Klebsiella. Outbreaks due to these and other organisms which are resistant to multiple antibiotics have been reported. Systemic prophylactic antibiotics do not decrease risk and may pre-dispose to superinfection; bladder irrigation with antibiotics not of proven value.

Prevention includes removal of Foley catheter when possible.

6. Nosocomial Wound Infection

Risk can be related to the type of surgical procedure performed: Clean Wounds—sterile site entered--risk 1-3%.

Clean-Contaminated--Respiratory, or GU tracts entered in controlled circumstances--risk ~ 4% .

Contaminated Wounds--Open, Accidental Wounds, Gross Spillage GI Tract, etc.--risk ~ 9%.

Dirty Wounds--infected site-risk ~ 13%.

Wounds can become infected at many times during hospitalization: The OR may serve as a source through contaminated instruments, personnel, etc.

As in urinary tract infections, patient's flora may contaminate the wound, however hospital organisms usually predominate with multiple antibiotic resistances.

When S. aureus or Group-A-beta-hemolytic Streptococci cause several infections, one should worry about personnel as carrier.

Prophylactic antibiotics administered at time of surgery have been shown to be of benefit in preventing some types of infections.

7. Nosocomial Respiratory Tract Infection

Coma, hypotension, tracheal intubation, antimicrobics, renal failure, metabolic acidosis, leukocytosis or leukopenia all are associated with colonization of the airway by Gram negative bacilli. Age > 70, thoracic or abdominal surgery associated with increased risk.

Colonization of airway does predispose to Nosocomial Pneumonia--23 per cent colonized develop pneumonia versus 4 per cent not colonized.

Decreased gastric acidity associated with increased risk of colonization.

In 1960's, outbreaks of Nosocomial Pneumonia were related to contaminated respiratory therapy equipment. With current usage of disposable equipment, this is less of a hazard.

Gut decontamination regimens recently fashionable, do not increase survival.

For some pathogens such as Pseudomonas or Acinetobacter the risk of death increases 2 fold.

Prevention includes prone ventilation, early extubation where feasible.

8. Primary Bacteremia

Primary bacteremia: not ascribable to another focus of infection, usually the result of a contaminated intravenous site or fluid (intra-arterial too!) or emanating from GI tract in neutropenic patient.

There are many different areas from bottle to intravascular segment that can become contaminated during the course of IV therapy.

Risk of IV infection related to type of cannula and duration in site.

Usual pathogens are S. aureus, Klebsiella, Pseudomonas, Enterococcus, Candida.

Antibiotic ointments at the site decrease bacterial colonization rates, local infection rates and local phlebitis.

There have been nationwide outbreaks of IV fluid infections related to contamination of IV bottle--unusual pathogens have been involved-- Enterobacter agglomerans, a plant pathogen, has been implicated in 3 epidemics, probably because of its ability to grow in D5W at room temperature.

9. Preventability

It has been demonstrated that “Awareness Programs” among Staff, Nurses, etc. can decrease the extent of NI.

Handwashing, which has been demonstrated to reduce transmission of organisms since 1600’s is not performed frequently or properly. Studies in ICU show that about 25-35% of patient encounters result in handwashing.

New alcohol based scrub – 10 second pump and distribute is superior to washing hands.

Prevention includes surveillance, education, teaching. Each hospital mandated to have infection control committee. Most have department with hospital epidemiologist, infection control practitioners.

10. Ancillary Material

10.1. Readings

10.1.1. Required

  • Schaecter, Chapter 72, pages 656-660.