Hospital Infection Control Team Research Articles

Application of exponential smoothing for nosocomial infection surveillance.

Detection of outbreaks of infection or increases in bacterial resistance to antimicrobial agents is an essential component of hospital infection control surveillance. The authors applied the method of exponential smoothing to microbiology data from 1987-1992 to investigate a suspected outbreak of gentamicin resistance among Pseudomonas aeruginosa bacteria at the Department of Veterans Affairs Medical Center, San Francisco, California, in 1991-1992. The years 1987-1990 were used to develop the baseline for the forecast model. Application of the model indicated that two observed prominent peaks in the annual cumulative incidence of gentamicin-resistant P. aeruginosa were within the upper bounds of their respective 95% confidence intervals as estimated by the forecast model--i.e., that no epidemic was in progress. This prediction was supported by investigations by the hospital's infection control team which indicated that the apparent increases were due to readmission of patients previously known to harbor these organisms. In contrast, application of a typically employed method that ignores the time series data structure indicated that there were 6 months in which incidence rates exceeded the upper bounds of their respective 95% confidence intervals, thereby erroneously suggesting that an epidemic was in progress. Recursive algorithms and some simplifying assumptions that do not affect the validity of inferences make the application of this method practical for nosocomial infection control programs.

Tracing the spread of methicillin-resistant Staphylococcus aureus by Southern blot hybridization using gene-specific probes of mec and Tn554.

In a community hospital in Brooklyn, New York, over a 3-year period, 79 methicillin-resistant Staphylococcus aureus (MRSA) isolates from five different case clusters were subtyped by Southern blot hybridization with two previously characterized gene probes, mec and Tn554. Together, the genotyping enabled the hospital infection control team to differentiate simultaneous MRSA clusters in the surgical intensive care unit (type I:A) and the open heart unit (type II:J), document the spread of one strain (type I:A) between roommates, identify an endemic strain (type II:J) from cardiac monitors and medical personnel, and identify an unrelated outbreak strain (type II:NH) in the labor and delivery unit. On the basis of this investigation it is clear that the routine DNA fingerprinting of MRSA in health care facilities, to monitor their spread and identify cases of nosocomial infections, is an important infection control measure.

Molecular technology for hospital epidemiology

Hospital-acquired infections in the United States contribute to ∼80,000 deaths per year, with an associated cost of >$4 billion. Some of these infections are associated with outbreaks and clusters occurring within the hospital. The hospital infection control team must respond quickly and decisively to recognize and curtail these outbreaks, but their response often depends on critical laboratory data that characterize or “fingerprint” suspected microbial isolates. This presentation summarizes the simple, easily performed tests and the more molecular approaches that a hospital laboratory may take in support of infection control efforts. In addition to phenotypic data, such as biotype and antibiograms, hospitals that elect to incorporate molecular protocols should limit their first experiences to plasmid analysis and plasmid restriction endonuclease profiles.

The effect of endogenous skin bacteria on burn wound infection.

Burn wound sepsis can be due to exogenous or endogenous bacteria. When rare organisms cause infection, exogenous sources are implicated. This sets into motion hospital infection control team searches, which are both exhausting and harassing to patients and staff. This study examines the skin bacteria present at admission and the frequency of endogenous infection in burn patients. Sixty-two patients with burns up to 92% of the total body surface area underwent unburned skin bacterial surveillance on admission and at weekly intervals using RODAC contact plates. Burn wounds were biopsied for quantitative and qualitative analyses. Morphologically dissimilar colonies were isolated and identified using standard gram-positive and gram-negative identification strips (Analytab Products, Inc. [API]). On admission, the patients harbored Staphylococcus species, many of which were burn wound sepsis were infected with the same organisms cultured from their unburned skin on admission. A subset of patients (14) grew methicillin-resistant Staphylococcus aureus from their wounds or other sites. A comparison with admission isolates showed identical susceptibilities. These data suggest skin is an endogenous source of infection in the burned patient.

A creative method for determining the immunization status of a community hospital medical staff

During 1985 and 1986, 191 of the 212 (90%) medical staff members in active private practice, who were surveyed responded to a one-page report regarding the status of their immunity and immunization to important infectious illnesses. Response rates were improved by including the survey form with the hospital privilege-renewal form that was required to be returned to the medical staff office. Of the respondents 96% reported prior history of chickenpox and 95% reported prior immunization to tetanus; of the 42 who reported prior bacille Calmette-Guérin (BCG) vaccination, only 17 reported a positive tuberculin skin test. An additional 32 medical staff members had a history of a positive tuberculin skin test with no prior BCG vaccination. Only 2 (1%) reported prior history of hepatitis B, and only 15 (8%) reported hepatitis B vaccination begun or completed at the time of the survey. This survey allows targeting of infection control activities, such as implementation of the hepatitis B vaccine promotion program and serologic testing of those with a negative history of chickenpox, to be developed for the medical staff. It allows the hospital infection control team instant access to data that can be simply obtained and updated regularly when information is needed about the immunization status of selected medical staff members during an outbreak situation.

Pseudomonas aeruginosa contamination of fibreoptic bronchoscopes

A pseudo-epidemic of Pseudomonas aeruginosa pulmonary infection was traced to a contaminated fibreoptic bronchoscope. A syndrome consistent with Ps. aeruginosa pneumonia developed in one immunosuppressed patient within 72 h of bronchoscopy. The controversy regarding proper cleaning, disinfection and sterilization guidelines for the fibreoptic bronchoscope is reviewed. Routine surveillance of bronchial wash cultures by the hospital infection control team is advocated to facilitate detection of a contaminated bronchoscope.