To determine the validity of an active, hospital laboratory isolate-based surveillance system in estimating rates of infection and to evaluate the use of surveillance data in describing institutional risk factors for increased rates of infection. Methicillin-resistant Staphylococcus aureus (MRSA) was chosen as the prototype organism for these evaluations.

Correlation Study: linear regression analysis and Student's t test were used to evaluate the correlation between number of MRSA isolates and number of MRSA infections in acute-care hospitals. Cross-Sectional Study: Student's t test, analysis of variance, and multiple linear regression analysis were used to evaluate the association between mean annual rate of MRSA blood isolates and institutional risk factors for increased rates of infection.

Acute-care hospitals, New Jersey.

The number of MRSA blood isolates was significantly correlated with MRSA blood infections (R, 0.78; P<01) and provided a good proxy measure for number of infections. Multivariate analysis demonstrated hospital location in the inner city (P= .02) and number of occupied beds (P<.01) to be independently associated with increased mean annual rates of MRSA blood isolates in acute-care hospitals.

This surveillance system is a valid tool for the estimation of institutional rates of infection and for the determination of institutional risk factors for increased rates of infection. It is ideal for further population-based investigations of antimicrobial-resistant bacteria.

To evaluate engineering control measures to prevent nosocomial transmission of diseases such as tuberculosis, we studied four portable high-efficiency air filtration units, including three high-efficiency particulate air (HEPA) filtration units, for their ability to remove aerosolized particles.

Studies were conducted in either a non-ventilated aerosol chamber or in a hospital isolation room that met CDC guidelines for TB control (negative pressure, ≧6 air changes per hour, air exhausted directly to the outside). The rooms were challenged with aerosolized mineral oil in the size range of 0.3 to 5.0 μm at levels 10 to 20 times the normal airborne particle load in the room at baseline. Airborne particles were counted with a laser counter capable of simultaneously measuring sizes ≧ = 0.3, ≧ 0.5, ≧ 1.0, and ≧ 5.0 μm. Experimental runs were conducted with the filtration units in the center or comer of the chamber or room, and the particle counter in the center of the room or at the exhaust vent.

Portable filtration units were effective in accelerating the removal of aerosolized submicron particles. In the nonventilated room, time required by the various portable filtration units for removal of 90% of aerosolized particles (≧ 0.3 μm) ranged from a low of 5 to 6 minutes to a high of 18 to 31 minutes, compared to the control (no filtration unit), >171 minutes. In the hospital room, individual filtration units removed 90% of aerosolized particles ( ≧ 0.3 μm) in times ranging from 5 to 8 minutes to 9 to 12 minutes, compared to the control (no filtration unit), 12 to 16 minutes. The location of the portable filtration unit (center versus comer) did not affect the clearance rate of airborne particles.

Our data indicate that portable filtration units can rapidly reduce levels of airborne particles similar in size to infectious droplet nuclei and, therefore, may aid in reducing the risk of tuberculosis exposure.

DNA amplification by the polymerase chain reaction (PCR) of human cytomegalovirus (CMV) nucleotide sequences recently has been reported for differentiation of CMV strains.

Retrospective study.

Evaluate the strain patterns of 15 CMV-positive buffy coat specimens from five pediatric bone marrow transplant patients.

Pediatric bone marrow transplant unit.

We performed PCR using primers corresponding to two distinct regions of the CMV genome, the major immediate-early (MIE) region and the a-sequence region, with subsequent restriction enzyme analysis of the amplified products.

Restriction enzyme analysis with Hae III and Hinf I of products amplified with nested PCR for the MIE region revealed distinguishable digestion patterns between patients but similar patterns for samples from each patient. All were distinct from the CMV Towne laboratory control strain. In contrast to these results, amplification of specimens with a-sequence primers, followed by restriction enzyme analysis, did not allow differentiation between all patients.

Our results indicate that nested amplification directly from buffy coat specimens using primers for the CMV MIE gene allows rapid CMV strain characterization that is useful for laboratory quality control and epidemiological studies. Distinct CMV strains were found in each patient, suggesting horizontal transmission was not responsible for acquisition of CMV infection in these patients.

To describe methicillin-resistant Staphylococcus aureus (MRSA) control in a hospital, including a surgical intensive care unit (SICU) outbreak.

Prospective surveillance of newly identified patients with MRSA. Barrier isolation (disposable gloves for direct contact with patient or immediate environment) was used for the routine care of hospitalized MRSA patients as of October 1991. Begirming in 1992, MRSA isolates were typed by restriction endonuclease enzyme analysis of plasmid DNA (REAP) and/or pulsed-field gel electrophoresis of genomic DNA (PFGE). Surveillance information and MRSA typing were used concurrently to identify nosocomial case clustering, confirm cross-infection, and support a need for additional outbreak control interventions.

University-affiliated public hospital.

Patients with newly identified MRSA colonization or infection from 1991 through 1993 and epidemiologically associated staff providing care to eight SICU patients in an outbreak.

Barrier isolation for affected and unaffected patients in and admitted to the SICU institution when the outbreak was identified and cross-infection confirmed. Anterior nares cultures of staff in contact with outbreak cases for detection of MRSA colonization.

Fifty-six hospitalized patients with community-acquired MRSA and 80 patients with nosocomial MRSA colonization or infection were identified during the 3 years. After the introduction of barrier isolation, the annual frequency of new nosocomial MRSA cases decreased and only one outbreak (eight cases in the SICU) caused by type-related isolates occurred, The other 35 nosocomial cases of MRSA during 1992 and 1993 were not epidemiologically related or were caused by isolates with different types. The SICU outbreak ended after instituting barrier isolation for all patients (with and without MRSA) in and admitted to the unit. Six colonized SICU staff were identified. All outbreak cases had identical or related MRSA types by PFGE and REAP. Staff isolates were different from case isolates by typing, and staff were not restricted and not given treatment for colonization. After more than 6 months of follow up, no further outbreaks of MRSA in the SICU or elsewhere in the hospital occurred despite returning to barrier isolation for affected patients only.

MRSA in hospitals and outbreaks of MRSA in ICUs can be controlled by surveillance and minimal barrier interventions. REAP or PFGE typing of MRSA can be used to support or refute the presence of cross-transmission. Typing also may be helpful when planning and assessing the effectiveness of interventions directed at endemic, as well as outbreak, MRSA control.