Colonization, Infection, and Molecular Typing of Methicillin-Resistant Staphylococcus Aureus (MRSA) in Children.

Staphylococcus aureus (SA) are responsible for both localized and invasive infections including carbuncles, cellulitis, lymph node abscess, and wound infections among others. SA is a ubiquitous environmental organism that colonizes 30-50% adults and more than 50% of children with underlying skin disorders. Hematogenous seeding can result in fulminant infection, and sites as diverse as bone, joint, lung, muscle, pericardium, endocardium, and other vascular structures can be involved. Factors which are known to increase the risk for colonization include the presence of underlying skin disorders and history of frequent needle use which occur in the setting of diabetes, or hemodialysis. Health care workers have traditionally been noted to have higher carriage rates.

MRSA strains emerged in the last two decades in the US and similarities to the evolution of penicillin resistant S. aureus were noted with colonization and infection in the hospital based setting noted first. Again, risk factors for MRSA colonization or infection in the hospital were noted to include prior antibiotic exposure, admission to an intensive care unit, surgery, and exposure to an MRSA-colonized patient. Emergence of CA-MRSA strains has been noted in the last decade having resistance to methicillin and erythromycin but susceptibility to clindamycin. These strains have challenged the practitioner's approach to the treatment of common skin and soft tissue infections as well as the management of invasive disease. The importance of such strains was underscored by the 1999 report detailing the deaths of 4 US children with invasive MRSA infection, none of whom had identifiable MRSA risk factors. Pulsed field typing of the isolates confirmed that these community strains were distinct from nosocomial strains isolated from patients in local hospitals.

This study seeks to more clearly define the prevalence of MRSA carriage; better identify risk factors through personal interview; and further identify resistance patterns and molecular strains. This data will guide physicians at Children's Mercy and in the community at large in choosing the best treatment option for children with MRSA infections.

The absence of traditional risk factors for MRSA infection has been noted in children with CA infections. Many studies that describe risk factors in MRSA patients do so by retrospective review of the medical record. Misclassification of patients may occur as physicians do not routinely document the presence or absence of such risk factors, particularly among household contacts.

This study will look at nasal colonization for 500 children in the Kansas City area to determine prevalence of MRSA colonization. During the study period, all invasive MRSA isolates will also be collected. Pulsed field typing will be done to determine whether the strains are community or healthcare associated and both groups will be compared.