S. aureus cultured from nares did not match wound isolates in many children with skin infections

Discordance between Staphylococcus aureus isolates cultured from nasal and wound sites and discrepancies between nasal colonization status and incidence of recurrent infections among children suggested that nasal colonization may not be an accurate marker for predicting which children are at risk for recurrent community-associated methicillin-resistant Staphylococcus aureus skin infections.

Researchers obtained cultures from 95 children, 93% of whom were black, with skin and soft tissue infections participating in a trial conducted to compare cephalexin and clindamycin as outpatient treatments.

MRSA was isolated from the wounds of 83 patients and from the nares of 40 patients. S. aureus was isolated from both wound and nasal cultures in 39 patients, but only 23 had isolates with identical methicillin susceptibility and pulsed field gel electrophoresis type from both sites. “A striking 33% of our patients either grew MRSA from their wound but methicillin-susceptible S. aureus from their nose or MSSA from their wound but MRSA from their nose,” the researchers wrote.

Furthermore, patients with MRSA isolates obtained from nasal culture after initial skin infection had a 19% recurrence risk compared with the 42% recurrence risk observed in patients without MRSA-positive nasal cultures.

“Taken together, these findings suggest that for community-[associated] skin and soft tissue infections, wound infection by MRSA — rather than nasal colonization with MRSA — may be a better predictor of children at higher risk of subsequent skin and soft tissue infection,” the researchers wrote. – by Nicole Blazek

Chen AE. Pediatr Infect Dis J. 2009;doi:10.1097/INF.0b013e31818cb0c4.

This is a small study involving mostly black children from a limited geographic area. A lot more work still needs to be done in different settings, because there are clearly differences between geographic areas and even within the same city. With the percentage of MRSA we’re isolating in three different hospitals here in New Orleans, there’s a difference of up to 40% between two of the hospitals.

This study suggests that patients are getting recurrences of MRSA infections from sources other than the nose, which we knew anyway because risk factors include close body contact with people that are infected, contaminated fomites or sports equipment. We should use caution in our interpretation until there are more data.

– George A. Pankey, MD

Ochsner Clinic Foundation, New Orleans