Aerosol survival of Staphylococcus epidermidis

Recent studies have suggested that aerosol dispersal might play a role in the dissemination of meticillin-resistant Staphylococcus aureus (MRSA). Relatively little has been published about the ability of staphylococci to survive in aerosols. This study measured the survival of Staphylococcus epidermidis, a surrogate for S. aureus, in aerosols and investigated the effect of relative humidity on survival. We used a Goldberg drum to assess survival at relative humidities of <20%, 40-60%, 70-80% and >90%. We controlled for the effects of aerosol dilution and physical decay by comparing the recovery of S. epidermidis with that of the aerosol-stable spores of Bacillus atrophaeus, using the ratio of their recovery rates to estimate biological degradation of S. epidermidis over time. At all relative humidities investigated 13% [95% confidence interval (CI): 10.1-16.2%] of the initial aerosol was recovered after 5h (300 min). The mean percentage survival ratio (% S. epidermidis:% B. atrophaeus) after 5h was 47% (95% CI: 33.5-60.5%). Overlapping 95% CIs of mean percentage survival ratios at each humidity level indicated that humidity did not have a significant effect on the survival in aerosol form of S. epidermidis. Additional experiments indicated that S. epidermidis was recoverable after five days at 76% humidity. The sizes of particles within the bacterial aerosol were well within the respirable range (<2.1 μm). The survival of aerosolised S. epidermidis demonstrated in this study suggests that staphylococci have the potential for aerosol dissemination in hospitals.