Background Within the current worldwide epidemic of community-acquired Staphylococcus aureus infections, attention has focused on the role of methicillin-resistant strains. We characterized methicillin-susceptible strains that also contribute. Methods We tracked cultures from abscesses submitted to the microbiology laboratory at St. Louis Children’s Hospital. We also sought Panton-Valentine leukocidin (PVL) genes in methicillin-susceptible Staphylococcus aureus (MSSA) isolates, and we further characterized some isolates by multilocus sequence typing (MLST), pulsed-field gel electrophoresis (PFGE), antibiotic susceptibility, accessory gene regulator (agr) allele, and presence of the arcA gene of the arginine catabolic mobile element (ACME). Results From 1999 to 2007, we detected a 250-fold increase in cultures of abscesses yielding methicillin-resistant Staphylococcus aureus (MRSA) and a 5-fold increase in abscess cultures yielding MSSA. MSSA isolates from abscesses and wounds were more likely to encode PVL than isolates from other sources. In contrast to PVL-negative isolates of MSSA which were genetically diverse, PVL-positive isolates were predominantly MLST 8, Agr type 1. More than half of PVL-positive MSSA isolates were resistant to erythromycin and susceptible to clindamycin with absence of inducible resistance, a pattern uncommon in PVL-negative MSSA but frequent in the USA300 clone of MRSA. In addition, PFGE of PVL-positive MSSA strains revealed the USA300 pattern. Conclusions In addition to methicillin-resistant strains, the current epidemic of Staphylococcus aureus infections includes infections caused by methicillin-susceptible strains that are closely related genetically and share phenotypic characteristics other than susceptibility to methicillin. These findings suggest that factors other than methicillin resistance are driving the epidemic.
Objectives Infections cause significant morbidity and mortality in neonatal intensive care units (NICUs). The association between nursery design and nosocomial infections has not been delineated. We hypothesized that rates of colonization by methicillin-resistant Staphylococcus aureus (MRSA), late-onset sepsis, and mortality are reduced in single-patient rooms. Design Retrospective cohort study. Setting NICU in a tertiary referral center. Methods Our NICU is organized into single-patient and open-unit rooms. Clinical datasets including bed location and microbiology results were examined over a 29-month period. Differences in outcomes between bed configurations were determined by Chi-square and Cox regression. Patients All NICU patients. Results Among 1823 patients representing 55,166 patient-days, single-patient and open-unit models had similar incidences of MRSA colonization and MRSA colonization-free survival times. Average daily census was associated with MRSA colonization rates only in single-patient rooms (hazard ratio 1.31, p=0.039), while hand hygiene compliance on room entry and exit was associated with lower colonization rates independent of bed configuration (hazard ratios 0.834 and 0.719 per 1% higher compliance, respectively). Late-onset sepsis rates were similar in single-patient and open-unit models as were sepsis-free survival and the combined outcome of sepsis or death. After controlling for demographic, clinical and unit-based variables, multivariate Cox regression demonstrated that bed configuration had no effect on MRSA colonization, late-onset sepsis, or mortality. Conclusions MRSA colonization rate was impacted by hand hygiene compliance, regardless of room configuration, while average daily census only affected infants in single-patient rooms. Single-patient rooms did not reduce the rates of MRSA colonization, late-onset sepsis or death.
Blood cultures positive for gram-positive cocci in clusters can pose a dilemma for empiric antimicrobial therapy because they could represent coagulase-negative staphylococcus or Staphylococcus aureus bacteremia. The GeneXpert MRSA/SA BC Assay (Cepheid, Sunnyvale, CA) is a polymerase chain reaction-based method for identifying S aureus and methicillin resistance that has been approved for use in adults, but data on its use in samples from pediatric patients is limited. We validated the Xpert MRSA/SA BC Assay for use with anaerobic and polymicrobial specimens from pediatric patients and implemented it for routine presumptive identification of S aureus in our pediatric hospital. The assay was 100% sensitive and specific for methicillin-resistant S aureus and 100% sensitive and 99.5% specific for methicillin-susceptible S aureus. Time to presumptive identification of S aureus bacteremia and determination of methicillin susceptibility was reduced by more than 24 hours. We found the Xpert MRSA/SA BC Assay to be a rapid, accurate tool for detecting methicillin-resistant and methicillin-susceptible S aureus in positive pediatric blood cultures, including polymicrobial cultures and those recovered in anaerobic blood culture media.
Objective.To determine the source of an outbreak of Salmonella javiana infection.Design.Case-control study.Participants.A total of 101 culture-confirmed cases and 540 epidemiologically linked cases were detected between May 26, 2003, and June 16, 2003, in hospital employees, patients, and visitors. Asymptomatic employees who had eaten in the hospital cafeteria between May 30 and June 4, 2003, and had had no gastroenteritis symptoms after May 1, 2003, were chosen as control subjects.Setting.A 235-bed academic tertiary care children's hospital.Results.Isolates from 100 of 101 culture-confirmed cases had identical pulsed-field gel electrophoresis patterns. A foodhandler with symptoms of gastroenteritis was the presumed index subject. In multivariate analysis, case subjects were more likely than control subjects to have consumed items from the salad bar (adjusted odds ratio [aOR], 5.3; 95% confidence interval [CI], 2.3-12.1) and to have eaten in the cafeteria on May 28 (aOR, 9.4; 95% CI, 1.8-49.5), May 30 (aOR, 3.6; 95% CI, 1.0-12.7), and/or June 3 (aOR, 4.0; 95% CI, 1.4-11.3).Conclusions.Foodhandlers who worked while they had symptoms of gastroenteritis likely contributed to the propagation of the outbreak. This large outbreak was rapidly controlled through the use of an incident command center.
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