Epidemiologic Similarities in Pediatric Community-Associated Methicillin-Resistant and Methicillin-Sensitive Staphylococcus aureus in the San Francisco Bay Area

Abstract

Risk factors differentiating methicillin-resistant Staphylococcus aureus (MRSA) from methicillin-sensitive S aureus (MSSA) infections in the pediatric community have been unclear. We performed a prospective case-comparison investigation of clinical, epidemiological, and molecular factors in pediatric community-associated (CA) MRSA and MSSA cases in the San Francisco Bay Area. Chart reviews were conducted in 270 CA-MRSA and 313 CA-MSSA cases. Fifty-eight CA-MRSA (21.4%) and 95 CA-MSSA (30.4%) cases were interviewed. Molecular typing was performed on 111 isolates. MSSA represented 53.7% of CA cases and was more likely to cause invasive disease (6.2% vs 1.1%, P=.004). Few potential epidemiologic risk factors distinguished CA-MRSA from CA-MSSA. No differences were found in factors related to crowding, cleanliness, or prior antibiotic use. Compromised skin integrity due to eczema (24.3% vs 13.5%, P=.001) was associated with CA-MSSA. Many exposures to potentially infected or colonized contacts or contaminated objects were assessed; only three were associated with CA-MSSA: having a household contact who had surgery in the past year (18.9% vs 6.0%, P=.02), and regular visits to a public shower (9.1% vs 2.0%, P=.01) or gym (12.6% vs 3.3%, P=.04). Molecular typing identified clonal complex 8 as the predominant genetic lineage among CA-MRSA (96.4%) and CA-MSSA (39.3%) isolates. In the context of recent heightened focus on CA-MRSA, the burden of serious disease caused by CA-MSSA among children should not be overlooked. MRSA and MSSA may be growing epidemiologically similar; thus, research, clinical, and public health efforts should focus on S aureus as a single entity.