To show the value of mathematical modeling in simulating the spread of nosocomial pathogens in an intensive-care unit (ICU), to provide a framework for listing available knowledge; to predict the benefits of various control measures; and to supplement the epidemiological assessment of these measures.

Simulated outbreak of a nosocomial pathogen in an ICU, based on a deterministic compartmental model describing both person-to-person spread and indirect spread between patients through staff members.

Simulation of three typical colonization control measures: effective handwashing compliance among staff members, ICU antimicrobial policy, and curtailing ICU admission of colonized patients.

In controlling colonization, effective handwashing compliance reduced staff member colonization, but only moderately limited patient colonization unless the ICU was isolated strictly by curtailing the admission of colonized patients. The impact of antibiotic policy was very slight.

In the field of nosocomial infection, mathematical modeling appears to be a valuable tool that can be used to evaluate the magnitude of the expected effects of control strategies and to guide the selection of the best randomized clinical trials to pursue.

To determine the incidence of, and risk factors for, nosocomial infections in neonates during and after treatment with extracorporeal membrane oxygenation (ECMO).

A retrospective cohort study of all infants treated with ECMO during a 4-year period.

26 neonates experiencing 32 nosocomial infections, and 54 neonates with no nosocomial infections.

A large, urban children's hospital.

30% of neonates treated with ECMO experienced at least one nosocomial infection. The rate of nosocomial infections was 10.3 per 1,000 patient-days. Risk factors significantly associated with nosocomial infection included duration of ECMO >7 days (mean, 12 vs 7 days; odds ratio [OR], 2.84; 95% confidence interval [CI95], 0.96-8.56); neonatal intensive care-unit stay >21 days (mean, 44 vs 19 days; OR, 8.73; CI95, 2.49-31.94); hospitalization >50 days (mean, 63 vs 29 days; OR, 5.44; CI95, 1.47-20.87); and surgical procedure before or during ECMO (46% vs 22%; OR, 4.58; CI95, 1.25 to 17.38).

Nosocomial infections occurred in 30% of patients undergoing ECMO. Although nosocomial infections were not associated with an increase in mortality, hospitalization was prolonged.

To determine glove use and handwashing practices, the factors associated with infection control practices, and the frequency of potential microbial transmission in a long-term–care facility (LTCF).

Observational study of 230 staff-resident interactions in an LTCF. We recorded resident characteristics, type of activity, staff credentials, and movements of the staff member's hands, then used the LTCF's guidelines to judge appropriateness of glove use and handwashing.

255-bed, university-based LTCF in Baltimore, Maryland.

A systematic sample of staff-resident interactions.

Gloves were worn in 139 (82%) of 170 interactions when indicated, but changed appropriately in only 21 (16%) of 132. Hands were washed when needed before an interaction in 27%, during an interaction in 0%, and after an interaction in 63%. Gloves were less likely to be used when caring for residents with gastrostomy tubes compared with other residents (relative risk, 0.85; 95% confidence interval, 0.73-0.98). Guidelines were followed more frequently during wound care than during other activities. Microbial transmission potentially could have occurred in 158 (82%) of 193 evaluable interactions.

We documented marked deficiencies in glove use and handwashing, demonstrated the possible impact of these deficiencies, and identified factors associated with inadequate handwashing and glove use. This information can be used in future educational and research efforts to improve infection control practices.

To monitor the epidemiology of invasive aspergillosis at a university hospital during a period of hospital construction. To compare the efficacy of active epidemiologic surveillance for invasive aspergillosis using Aspergillus cultures with the efficacy of surveillance using Aspergillus antigen detection.

A prospective surveillance study.

An 850-bed, tertiary-care, university-based hospital.

A convenience sample of 153 patients with Aspergillus antigen testing and culture.

24 cases were identified over a 12-month period; 7 were nosocomial, and 17 were community-acquired. Cases occurred primarily in patients with hematologic malignancy, but also occurred in patients with solid tumor, steroid treatment, cardiac transplant, and acquired immunodeficiency syndrome. Culture techniques identified only 14 (58%) of 24 cases, whereas Aspergillus antigen was positive in 19 (79%) of 24 cases tested. Epidemiological surveillance using either antigen or culture positivity detected 22 (92%) of 24 cases. In addition, antigen detection was 98% specific for the detection of aspergillosis, as compared to 91% for culture and 88% for antigen and culture combined.

Hospital surveillance for aspergillosis should include determination of whether cases are nosocomial or community-acquired, because many may be the latter. Patients at risk for aspergillosis include patients without hematologic malignancies. Enhanced case detection occurred with active surveillance of patients considered to be at risk using both fungal serology and traditional microbiological techniques. Antigen detection was more sensitive and specific for the detection of invasive aspergillosis and may improve epidemiological surveillance for aspergillosis.

To evaluate the risk of nosocomial transmission of parvovirus B19 (B19) infection to healthcare workers (HCWs) exposed to patients with transient aplastic crisis (TAC) caused by acute B19 infection.

Cohort study.

1,000-bed, urban teaching hospital in Atlanta, Georgia.

Eighty-seven exposed HCWs who cared for two patients with TAC prior to the time they were isolated and a comparison group of 88 unexposed HCWs from wards or clinics where the patients did not receive care.

Self-administered questionnaire on hospital contact with index patients, B19 community risk factors, and signs and symptoms suggestive of B19 disease. Serology for B19-specific IgM and IgG antibodies measured by antibody-capture enzyme-linked immunosorbent assay.

1 (3.1%) of the 32 nonimmune exposed HCWs had serologic evidence of recent B19 infection compared to 3 (8.1%) of the 37 nonimmune HCWs in the comparison group (P=.6). In a subgroup analysis of exposed HCWs who cared for index patients during the time when the virus load was expected to be greatest, a recent infection rate of 5.8% (1/17) was found among nonimmune HCWs.

The finding of similar rates of recent infection in nonimmune exposed and unexposed HCWs suggests that transmission to HCWs did not occur, despite failure to place the patients in isolation at the onset of hospitalization.

To investigate a mixed Salmonella heidelberg and Campylobacter jejuni foodborne outbreak in a nursing home.

Retrospective cohort study with a nested case-control design. Cases were defined by positive stool-culture results. Controls needed to be both asymptomatic and culture-negative.

Residents of a 580-bed nursing home in Brooklyn, New York.

Of the 580 residents, 119 (21%) developed illness. Of the 93 symptomatic patients who submitted specimens, cultures were positive for S heidelberg in 24 (26%), C jejuni in 14 (15%), and both microorganisms in 25 (27%).

Only the pureed diet was associated highly with infection by either Salmonella (odds ratio [OR], 17.6; 95% confidence interval [CI95], 4.8-68.7; P<.001), Campylobacter (OR, 13.3; CI95, 3.2-59.2; P<.001), or both organisms (OR, 8.9; CI95, 2.7-30.3; P<.001). Among the 52 pureed foods served during the 5 days before the outbreak, five meat or poultry items were associated most strongly with culture positivity.

Of these five meat items, only a chopped-liver salad was implicated by the two employees reporting illness. A reported food-handling error occurred when ground, cooked chicken livers were placed in a bowl containing raw chicken-liver juices.

Recommendations for proper cleaning and sanitizing of kitchen equipment to prevent cross-contamination between raw and cooked foods.

Mixed foodborne outbreaks occur rarely. During this outbreak, contamination of a single food item with multiple bacterial pathogens was the likely source of transmission. Improper food-handling techniques that promote growth of one microorganism also allow growth of other pathogens that may be present. Because different sources and routes of transmission may be implicated for different pathogens, specific preventive measures may vary depending on the organisms involved.

To quantify specific factors believed to increase healthcare worker (HCW) risk for contaminated sharps injuries (eg, visibility, communication, and range of motion); to quantify the degree to which respirators of various designs impacted those same factors; and to assess HCW opinions about the suitability of selected respirators with respect to patient care and user compliance criteria.

Sharps injury data from seven hospitals were analyzed to determine the potential contribution of visibility, communication, and range of motion to reported injuries. Healthcare workers representing various clinical specialties and physical characteristics were examined at baseline and while wearing five different respirators to quantify the impact of respirator design on visibility, communication, and range of motion. Healthcare workers were inter viewed and completed a survey assessing each respirator.

Hospital and ambulatory-care settings.

Population-based and convenience sample.

Communication, visibility, and range of motion were found to affect contaminated sharps injuries significantly. Selected high-efficiency particulate air (HEPA) respirators were found to have a negative impact on each of these variables. Healthcare workers involved in the study also reported compliance criteria problems with selected HEPA respirators, which may effect implementation of respiratory precautions adversely.

Current HEPA respirators, because of their design, potentially increase the risk of bloodborne pathogen exposure through sharps injuries. We conclude that mandating respirators without regard to the potential impact of their design to the sharps injuries may be counterproductive to HCW safety, because they may increase, rather than decrease, overall occupational risk to HCWs.

To describe the investigation of a pseudo-outbreak of multiresistant Pseudomonas aeruginosa fecal colonization in a hematology unit.

Retrospective chart review; prospective environmental sampling and observation of stool culture technique; genotyping by random arbitrary primer polymorphic DNA polymerase chain reaction (RAPD-PCR).

An academic tertiary-care hospital.

Between August and October 1994, P aeruginosa resistant to imipenem, ceftazidime, ciprofloxacin, and all aminoglycosides was isolated from surveillance stool cultures from 10 neutropenic patients cared for in the hematology unit. P aeruginosa, with an identical susceptibility pattern, was isolated from three patients admitted to the same unit in the year before the “outbreak.” Two months before the outbreak, 12 healthcare workers had been added to the staff.

Observation of stool sampling techniques as performed by healthcare workers revealed that samples for surveillance cultures were taken from feces in the toilet. When the proper sampling technique was used, P aeruginosa was not isolated from stool samples from 8 of 10 patients with previously positive cultures. P aeruginosa also was isolated from two wash basins, toilet flushing water, and a toilet brush. Genotyping by RAPD-PCR showed that the isolate from the toilet flushing water was identical to the P aeruginosa strains of eight patients from the outbreak.

This pseudo-outbreak emphasizes the importance of proper sampling techniques and that periodic observation may be necessary to verify proper sampling techniques.