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Objective: To describe the epidemiology and the interventions used to control two methicillin-resistant Staphylococcus aureus (MRSA) epidemics involving 46 infants with two fatalities in a neonatal intensive care unit (NICU)., Setting: A 50-bed, level III NICU in a university hospital., Interventions: After traditional interventions failed to stop the first epidemic, an intensive microbiologic surveillance (IMS) program was developed. Cultures were obtained on all infants each week, and those colonized with MRSA were isolated. When an infant was found to be colonized with MRSA, cultures immediately were obtained on all surrounding infants. This was continued until no MRSA-colonized infants were found in the area. During the first epidemic, mupirocin was used in an attempt to eradicate the organism from the unit., Results: All infants, colonized and noncolonized, and parents of and personnel working with colonized infants were treated simultaneously with 5 days of mupirocin. This failed to eradicate MRSA in colonized infants. The spread of MRSA ceased in the unit, but a second epidemic occurred 4 months later. This time, IMS alone was successful in quickly containing the epidemic, and MRSA disappeared from the unit after all colonized infants were discharged. Plasmid analysis demonstrated that the same strain was responsible for both outbreaks., Conclusions: IMS and isolation are effective in containing the spread of MRSA in an NICU. The use of mupirocin failed to eradicate the organism.

OBJECTIVE--To compare the accuracy of clinical epidemiologic findings with results of molecular epidemiologic analysis in identifying the source of recurrent epidemics of erythromycin-resistant Staphylococcus aureus (ERSA) infections in a well-baby nursery. DESIGN--Epidemic investigations with retrospective and prospective microbiological surveillance. Staphylococcus aureus isolates were evaluated by plasmid analysis and genotyping. SETTING--A well-baby nursery in a 700-bed university teaching hospital with approximately 250 deliveries per month. PATIENTS--Newborn infants who developed ERSA infections during 1990 and 1991. INTERVENTION--Traditional infection control measures, including cohorting of infected infants and hand washing, were implemented. Personnel were cultured for nasal carriage of S aureus during both epidemics. Employees carrying ERSA were removed from the nursery and treated with mupirocin. RESULTS--In the first epidemic, 15 infants were infected with ERSA. A nursing assistant who cared for most of the infants was found to be a carrier of ERSA. She was removed from the nursery and the epidemic resolved. Fifteen months after the first epidemic ended, an epidemic that involved 11 infants began. The attending physician had a facial furuncle and was found to be a carrier of ERSA. The physician was treated and the epidemic resolved. Plasmid and genotyping showed the ERSA organisms from both epidemics were the same. The employee implicated in the first epidemic did not have the epidemic strain, but the physician who attended during both epidemics did. CONCLUSIONS--Traditional epidemic investigations may lead to false conclusions that can only be recognized with molecular epidemiologic techniques. For these techniques to be useful in the control of outbreaks, plasmid analysis and/or genotyping must be readily available.

An epidemic of methicillin-resistant Staphylococcus aureus (MRSA) infections involving 323 patients occurred at the University of Cincinnati Hospital from 1977 to 1981. Subsequently, endemic MRSA persisted in the hospital for 6 years, until 1987, when a new epidemic began with 223 patients becoming infected over 3 years. Between the two epidemics, there was a major change in the MRSA recovered from infected patients, as demonstrated by three epidemiologic markers. Antibiograms showed that the tetracycline-resistant MRSA involved in the first epidemic was replaced by tetracycline-susceptible MRSA in the second epidemic; bacteriophage typing indicated that the original epidemic strain, D11/83A/85, had been replaced by new strains, many of which were susceptible to phage 54; and restriction endonuclease analysis of plasmid DNA confirmed that a single strain was involved in the first epidemic and that multiple strains were present in the second epidemic. The epidemiology of MRSA infections in the hospital changed with the change in staphylococcal strains. The first epidemic was hospital based with most infections occurring in surgical patients, and the burn unit was the major reservoir. In contrast, 28% of the patients in the second epidemic had community-acquired infections, and nursing home patients were an important source of these infections. Also, 29% of the hospital-acquired infections in this epidemic occurred in nonsurgical patients. This time the burn unit was not a reservoir of infection, but other intensive care units were. The increased diversity of strains of MRSA in the second epidemic might be related to increased transmission in the community and more widespread transmission in the hospital.

During a three-year period, Staphylococcus aureus phage type D11/83A/85 that was resistant to methicillin, cephalothin, and multiple aminoglycosides was recovered from 260 infected patients in an urban general hospital in Cincinnati, Ohio. This methicillin-resistant S. aureus (MRSA) was recovered from 30% of all blood cultures positive for S. aureus and represented 50% of all episodes of nosocomial bacteremia due to S. aureus. Bacteremia due to MRSA occurred most often in surgical patients (especially burn patients), occurred late in hospitalization, and was recovered frequently from wounds and intravascular catheters. Infection with S. aureus was the direct cause of death of 44% of the patients with bacteremia due to MRSA. Nine of 10 MRSA-infected patients who were treated with vancomycin alone responded to therapy compared with seven of 15 who were treated with other antistaphylococcal antibiotics (P less than 0.05). The present study defines the epidemiologic characteristics of bacteremia due to MRSA, demonstrates the virulence of MRSA, and proves that vancomycin is effective as therapy.

Serum samples taken from women with toxic-shock syndrome (TSS) and from women without a history of TSS were examined for the presence of antibodies to toxic-shock-syndrome toxin (TST). Serum samples from 38 women with TSS and from 70 women with no history of TSS were analyzed by radioimmunoassay (RIA) and by an enzyme-linked immunoadsorbent assay (ELISA). Antitoxin titers obtained by the assays were highly correlated. Antibody levels in sera of women with TSS, or a history of TSS, were significantly lower than levels in sera of women with no prior evidence of TSS. The mean level of antitoxin titers in the total sample of acute, convalescent, and recovered TSS groups was significantly lower than that of the control groups, which consisted of 31 carriers of genital Staphylococcus aureus and a similar number of age- and race-matched noncarriers. Although a trend toward elevated antitoxin titers was apparent after recovery, no vigorous immunologic response to TST was noted. In contrast, the majority of healthy women demonstrated measurable antitoxin titers, a finding indicative of current or prior colonization with TST-producing strains of S. aureus. The data suggest that absence of antibodies to the TSS toxin may be a predisposing factor in the development of clinical disease.

From 1977 to 1981, 317 patients in a large general hospital became infected with methicillin- and gentamicin-resistant Staphylococcus aureus. The epidemic strain was characterized as bacteriophage type D11/83A/85, resistant to methicillin, cephalosporins and aminoglycosides, and contained a 24 megadalton plasmid which mediated gentamicin resistance. Spread within the hospital followed introduction of this organism into the general surgical and burn services and resulted from cross infection between patients. These services remained a reservoir of infection throughout the four-year period. Only 2% of hospital personnel carried methicillin-resistant S. aureus in their anterior nares, and only one of them was shown to be a long-term carrier. During the epidemic, there was no overall increase in serious staphylococcal infections, as reflected in bacteremias. As methicillin-resistant S. aureus increased, there was a reciprocal decrease in methicillin-sensitive S. aureus. Later, as methicillin-resistant S. aureus bacteremias decreased, methicillin-sensitive S. aureus bacteremias increased. Attempts to control the spread of the organism by containing infected patients on an isolation ward, or by placing all such infected patients in strict isolation, decreased the frequency of infections, but did not eliminate the organism. In 1980, the burn service was separated from the surgical service and moved into a new burn unit. Also, the five-bed rooms in the hospital were being converted to two-bed rooms. With only routine isolation precautions, the epidemic resolved over the next year, although the epidemic strain persists in the hospital.

Experience with Staphylococcus aureus infections in a hemodialysis unit in which arteriovenous fistulas were used routinely for dialysis is reviewed, including an epidemic involving multiple bacteriophage types. Most infections involved the fistula site and were associated with bacteremia, although bacteremia without an obvious fistula infection did occur. Despite recurrent bacteremia, endocarditis was not documented, and patients did not develop teichoic acid antibodies as measured by an immunodiffusion technique. Patients with fistula infections responded to antibiotic therapy and did not require removal of the fistula except in two patients whose fistulas ruptured. Patients with shunt infections had to have their shunts removed to control infection. The epidemic developed after the hemodialysis unit was moved into a larger area to facilitate an increasing number of patients and after diabetic patients were admitted to the dialysis program. Both autoinfection and cross-infection contributed to the epidemic, which resolved with improvements in aseptic techniques. A culture survey indicated that the nasal carriage of staphylococci was not unusually high during the epidemic. This report emphasizes that staphylococcal infections remain a problem in continually changing hospital environments.