Recovery of Staphylococcus aureus from environmental surfaces in a high school and on playgrounds

Background: There have recently been a number of reports of community-associated methicillin-resistant Staphylococcus aureus (MRSA) infections in school-age children. Because S. aureus may survive for prolonged periods on surfaces, there is uncertainty regarding whether environmental surfaces in schools and on playgrounds could potentially serve as sources for transmission.

Objective: To perform a culture survey to assess recovery of S. aureus from environmental surfaces in a high school and on playgrounds, and to assess survival of MRSA on surfaces.

Methods: Sterile swabs were used to collect cultures from environmental surfaces inside a high school, on outdoor playgrounds associated with schools, and on indoor playgrounds associated with restaurants. Swabs were plated onto CHROMagar S. aureus selective media and isolates were subjected to identification and susceptibility testing using standard methods. To assess survival on surfaces, MRSA strains were inoculated onto dry or moist (i.e., nutrient-free agar) surfaces and recovery was monitored over time.   

Results:  Of 150 environmental cultures collected from the high school, none were positive for MRSA and only 4 (3%) were positive for methicillin-susceptible S. aureus (MSSA), including 2 wrestling mats, 1 student desk, and 1 chair arm rest. Of 52 cultures collected from outdoor playgrounds adjacent to schools, none were positive. However, 4 of 133 (3%) cultures collected from 4 indoor playgrounds associated with restaurants were positive for MRSA.  On dry surfaces, the number of colony-forming units (CFU) of MRSA recovered by swabs decreased rapidly over time (1,000 fold by 3-6 days after inoculation), whereas on moist nutrient-free agar no significant decrease in recovery occurred during a 2-week period.

Conclusions: Recovery of S. aureus from environmental surfaces in a school and from playgrounds was uncommon, and MRSA was only recovered from indoor playgrounds associated with restaurants. Because survival is prolonged on moist surfaces, it would be reasonable to focus environmental disinfection efforts primarily on areas that are moist and/or frequently come into contact with poorly covered skin.