Materials and Methods
Patients and Designs
Chang Gung Children's Medical Center is a university-affiliated teaching hospital, situated in northern Taiwan, which provides a range of care, from primary to tertiary care, and is a part of Chang Gung Memorial Hospital. There are 3 level III NICUs, distributed on 2 floors, in this Children's Medical Center. Currently, there are 17, 20 and 12 beds in NICU-1, NICU-2 and NICU-3, respectively. The disease severity of infants in NICU-3 is relatively mild. In NICU-1 and NICU-2, there is 1 single-bed room, 1 two-bed room and others are wards. The distance between isolettes is 2 m. There is a sink available between 2 isolettes, and alcohol-based hand rub is available for each bed. During the study period, the nurse-to-infant ratio was 1:2, and the units were staffed by both residents and fellows. This study was among the institution's quality improvement programs proposed by the institution's infection control committee and was approved by the institutional review board of Chang Gung Memorial Hospital, and the institutional review board agreed that the need for written informed consent from the participants could be waived.
From November 2007 to October 2008, all the infants admitted to NICU-1 and NICU-2 were included consecutively. From the previous surveillance study, we learned that nearly 90% of the MRSA colonized infants are detected within the first 2 weeks of admission, and sampling of both nares and umbilicus is adequate for surveillance cultures (negative predictive value 93%) in this population. Hence, in this study, specimens from nares and umbilicus were obtained within 24 hours of admission, and specimen collection was repeated weekly for 2 weeks. For the infants colonized with MRSA and still staying in NICUs, decolonization procedures with topical mupirocin ointment for both nares and umbilicus were administered with a cotton swab twice daily for 5 consecutive days if the infants still stayed in NICUs at the time MRSA was identified. Follow-up cultures were then obtained 1 week later, repeated once weekly and were discontinued if 2 consecutive cultures were negative for MRSA. Repeated decolonization procedures were performed again if the follow-up cultures still yielded MRSA. During the study period, each study infant received disinfectant bath with soap and baby lotion once daily. For comparison (switched over study), the decolonization procedures were performed in NICU-1 only during the first 6 months, and then during the second 6 months, the decolonization procedures were implemented in NICU-2 only. Once the study infant was designated into either treatment or no-treatment group, the infant was classified in the same group throughout the hospitalization, even when transferred to other wards.
All the study infants were observed to evaluate if they encountered MRSA infection throughout the hospital stay, even when transferred to other wards. MRSA isolates recovered from clinical diagnostic samples (beyond surveillance culture specimens) submitted to the clinical microbiologic laboratory were regarded as clinical isolates. Any infant with clinical isolates of MRSA identified 48 hours after admission, and who had compatible clinical manifestations and received an in vitro susceptible antimicrobial therapy, was categorized as experiencing an episode of infection. Episodes of MRSA infection involving a single infant were considered to be distinct if they were ≥2 weeks apart, a course of effective antibiotics had been administered, the clinical symptoms had resolved and ≥1 negative culture from the infected site was documented. All the clinical isolates and all the colonized isolates from the patients with clinical MRSA infection were molecularly characterized. For a colonized infant with clinical isolates, the genetic relatedness of both the colonized and clinical isolates was compared. Also, susceptibility to the study medication, mupirocin, of the isolates was determined by E-test.
Laboratory Procedures
Surveillance specimens for culture were obtained with a cotton swab, placed in transport medium of Venturi Transystem (Copan Diagnostics, Brescia, Italy) and then processed in our microbiology laboratory within 4 hours. Identification of MRSA was confirmed according to Clinical Laboratory Standards Institutes guidelines. Briefly, each specimen was incubated at 37°C overnight with 5% sheep blood agar plate (BD Diagnostics, Sparks, MD). Based on the patterns of beta-hemolysis and the macroscopic appearance, the suspected colonies of S. aureus were further incubated with 5% sheep blood agar plate at 37°C overnight. Then, coagulase test was conducted using rabbit plasma to ensure the identification of S. aureus. Cefoxitin test was then used to distinguish the MRSA from methicillin-susceptible S. aureus. Molecular methods included pulsed-field gel electrophoresis (PFGE) with SmaI digestion, staphylococcal chromosomal cassette (SCCmec) typing and multilocus sequence type. In addition, the presence of Panton–Valentine leukocidin genes was also examined. All the procedures were described previously. The genotypes of PFGE were designated, as in our previous studies, in alphabetical order; any new type, if identified, was designated consecutively. PFGE patterns with <4-band differences from an existing genotype were defined as subtypes of that genotype and were labeled with Arabic number suffixes. Two isolates were considered to be indistinguishable, highly related or distinct if they had the same subtype (no band difference), the same genotype (<4-band differences) or a different type (≥4-band differences), respectively.
Statistical Analysis
We compared the characteristics of the infants with and without MRSA colonization by means of χ (continuity-adjusted) or Student t tests. Relative risk and/or odds ratios (ORs) were calculated with 95% confidence intervals (CIs). Statistical analyses of the data were performed with Release 10. (StatsCorp LP, College Station, TX).