Prevalence of methicillin-resistant Staphylococcus aureus colonization in children and adolescents admitted to CHEO

Abstract

Little is known about the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in Canadian paediatric populations. A prospective prevalence survey of MRSA colonization was conducted on all children (excluding psychiatric inpatients) admitted to the Children’s Hospital of Eastern Ontario (CHEO; Ottawa, Ontario) over a 30-day period in the summer of 2008. Patients meeting infection prevention and control criteria for targeted MRSA screening (ie, transfers from other hospitals, hospitalization outside CHEO within the past six months, or known MRSA-positive status) were screened with nasal and rectal swabs, independently of the study protocol. All other study participants had nasal swabs collected plus perianal swabs, if specific consent was provided. All specimens were obtained within 48 h of admission to exclude nosocomial acquisition. Of 417 eligible admissions in the study period, 241 were screened for MRSA. Ninety-eight (24%) were discharged or could not be enrolled before 48 h, 35 (8%) were not interested in learning about the study and 43 (10%) refused consent. Both nasal and rectal/perianal specimens were obtained from 126 patients, and only nasal specimens were obtained from the remaining 115 patients. Only one patient was colonized with MRSA, representing 0.2% of all admissions in the 30-day period, and 0.4% (one of 241 patients; 95% CI 0% to 1.2%) of all screened patients. This child had MRSA recovered only from her nose. Historically, MRSA has been infrequently isolated from CHEO inpatients; a recent study (1) identified 44 cases of either MRSA infection or colonization in admitted children between 1990 and 2009, although the incidence appeared to be increasing. Our study also demonstrated that MRSA colonization in children and adolescents at admission to CHEO is rare. Health care exposure is a significant risk factor for MRSA colonization, with MRSA prevalence being substantially higher in patients screened at hospital admission than among those screened in the community (2,3). It is, therefore, likely that less than 0.4% of the general paediatric population of eastern Ontario is colonized with MRSA, unless there is something unique about the colonized children that results in them being hospitalized less often than those not colonized. In addition to a small sample size and limited study period, only 58% of all admissions were screened, possibly leading to omission bias. We note, however, that the largest group that was not captured in the study were those discharged before attempted enrollment – the majority of whom underwent elective, short-stay surgical procedures. We do not believe that this population would have substantially higher risks for MRSA colonization than the inpatients captured in the study; there were no inpatient specimens that were positive for MRSA during the study period. As well, although one-half of the patients screened had only a nasal swab performed, the true prevalence is not likely to be significantly greater or clinically relevant if the sensitivity of nasal screening is approximately 70% (4–7). Based on our results, the prevalence of MRSA colonization in children from eastern Ontario was substantially lower than that reported in American paediatric populations (8). Although nasal carriage is not a sine qua non for MRSA infection (9), higher colonization rates are associated with higher rates of infection in a given population, and those colonized are more likely to become infected (8,10–13). Consequently, our data have implications relating to the likelihood of MRSA infection in children from eastern Ontario. Carriage rates will almost certainly progressively increase, however, and ongoing surveillance will be necessary.