To determine risk factors for central venous catheter-associated bloodstream infections (CVC-BSI) during a protracted outbreak.

Case-control and cohort studies of surgical intensive care unit (SICU) patients.

A university-affiliated Veterans Affairs medical center.

Case-control study: all patients who developed a CVC-BSI during the outbreak period (January 1992 through September 1993) and randomly selected controls. Cohort study: all SICU patients during the study period (January 1991 through September 1993).

CVC-BSI or site infection rates, SICU patient clinical data, and average monthly SICU patient-to-nurse ratio.

When analyzed by hospital location and site, only CVC-BSI in the SICU had increased significantly in the outbreak period compared to the previous year (January 1991 through December 1991: pre-outbreak period). In SICU patients, CVC-BSI were associated with receipt of total parenteral nutrition [TPN]; odds ratio, 16; 95% confidence inter val, 4 to 73). When we controlled for TPN use, CVC-BSI were associated with increasing severity of illness and days on assisted ventilation. SICU patients in the out-break period had shorter SICU and hospital stays, were younger, and had similar mortality rates, but received more TPN compared with patients in the pre-outbreak period. Furthermore, the patient-to-nurse ratio significantly increased in the outbreak compared with the pre-outbreak period. When we controlled for TPN use, assisted ventilation, and the period of hospitalization, the patient-to-nurse ratio was an independent risk factor for CVC-BSI in SICU patients.

Nursing staff reductions below a critical level, during a period of increased TPN use, may have contributed to the increase in CVC-BSI in the SICU by making adequate catheter care difficult. During healthcare reforms and hospital downsizing, the effect of staffing reductions on patient outcome (ie, nosocomial infection) needs to be critically assessed.

To assess the ability of a protective isolation room ventilation system to reduce patient exposure to airborne infectious agents, using a small-scale model that permits cost-effective and unobtrusive study of relevant indices of performance.

A one-half scale model of a protective isolation room at the University of Minnesota Hospital was constructed and equipped for tracer gas experiments to assess ventilation efficiency.

Tracer gas (SF6) was injected into the model supply air. Tracer gas concentration was recorded over time and analyzed to determine local and room mean age of air. Age of air is a direct measurement of ventilation efficiency and can be used to predict patient exposure to contamination.

Although for the room taken as a whole, ventilation efficiency was close to 50% (a value corresponding to perfect mixing), the experimental results for the local mean age of air indicate that some parts of the model were ventilated much better than others.

Room air exchange rate is only one parameter useful in assessing ventilation in patient areas. Effective distribution of ventilation air also is critical to the control of airborne contamination. Areas of the room with poor ventilation would be expected to have higher concentrations of airborne infectious agents and other contaminants. Patient exposure can be minimized by placing the patient in well-ventilated areas of the room. Improved ventilation designs may reduce patient exposure further without increasing actual airflow rate.

To determine the effect of different methods of training on the ability of hospital workers to wear respirators and pass a qualitative fit test, and to compare the direct cost of the training.

179 hospital employees were recruited for study and were stratified into three groups based on the type of training they received in the use of respirators. Employees in Group A received one-on-one training by the hospital's industrial hygienist and were fit tested as part of this training. Employees in Group B received classroom instruction and demonstration by infection control nurses in the proper use of respirators, but were not fit tested as part of training. Employees in Group C received no formal training. Each participant in our study underwent a subsequent qualitative fit test using irritant smoke to check for the employee's ability to adjust correctly the fit and seal of the respirator. The direct cost of each method of training was determined by accounting for the cost of trainers and the cost of employee-hours lost during training.

775-bed Veterans' Affairs hospital.

94% of Group A participants (49 of 52) passed the qualitative fit test, compared to 91% of Group B participants (58 of 64) and 79% of Group C participants (50 of 63; P=.036, 2 × 3 chi-square). Group A had a significantly higher pass rate than Group C (P=.043), but Group B did not differ significantly from Group A or Group C. Location or professional status did not affect pass rate, but prior experience wearing respirators did. When the study groups were compared after stratifying for prior experience, we found no difference in pass rates, except when Groups A and B (those with any training) were combined and compared with Group C (107 of 116 versus 50 of 63, P=.05, Mantel-Haenszel chi-square).

We estimate that the method of training involving individual instruction followed by fit testing took 20 minutes per employee to complete, compared to 10 minutes per six employee class for the method of classroom demonstration. The difference in direct cost between the two methods, applied to the training of 1,200 employees at our hospital, would be approximately $19,000 per year.

Our study indicates that training in the proper use of respirators is important, but the method of training may not be, as the two methods we evaluated were nearly equivalent in their pass rates on fit testing (94% versus 91%). Fit testing as part of training may have enhanced the performance of our participants marginally, but was more time consuming and accounted for most of the excess cost.

To describe long-term trends in nosocomial infection rates and the threshold testing method for evaluating nosocomial sur veillance data in a long-term–care facility (LTCF).

Descriptive epidemiology of prospectively collected infection control sur veillance data and application of threshold testing for detecting possible outbreaks. Threshold testing uses the binomial distribution to calculate probabilities of infection frequency at selected endemic levels (mean number of infections per month) and compares these probabilities to obser ved infection frequency.

One hundred twenty-bed LTCF located within a public, university-affiliated hospital.

The study period was 1987 through 1994. Yearly endemic levels of specific types of infection were calculated and threshold levels were determined using a previously published method. In this study, a probability of P=.01 was chosen to determine the threshold at a specific endemic level; if the observed number of infections in a month reached or exceeded the threshold level, the likelihood that this occurred by chance alone was 1% or less.

None.

The overall mean nosocomial infection rate ranged from three to five episodes per 1,000 resident care days per year; mean yearly rates from 1990 onward were higher and more stable than those from 1987 to 1989. The most common infections identified were lower respiratory tract, skin and soft tissue, urinary tract, and conjunctivitis. For each of these infections, threshold levels were calculated periodically, using only the monthly frequency of infection. Despite variations in the yearly mean endemic level of various infections, threshold levels were stable except for skin and soft-tissue infection.

Threshold testing for analysis of infection control sur veillance data in the LTCF setting is straightfor ward and does not require knowledge of statistics, special computer software, or calculation of rates; given the stable population in the typical LTCF, threshold testing can be based on variations in the monthly count of infections and provides an objective evaluation of surveillance data and a method to identify when outbreaks may be occurring.