The microorganisms of indoor air in a teaching hospital

Objectives: The purpose of this study was to determine the level and species of air microorganisms in a teaching hospital so that improvements in air quality could be made. Methods: A one-stage Andersen microbial particle sizing sampler was used to sample the air at five units in this hospital. On the basis of these results, consecutive sampling and analyses were conducted at one of the locations where the highest microbial levels were found. Results: The levels of air bacteria in the respiratory care ward were comparatively high: daytime levels exceeded the low bacteria standard of 200 cfu/m³, and the peak level of 934 cfu/m³ occurred between 1300 and 1500 h. Total bacterial counts correlated positively with relative humidity and the level of carbon dioxide (P<0.01). Coagulase-negative Staphylococci (31.3%) and Staphylococcus aureus (18.8%) were commonly detected in the air of the respiratory care ward, and the dominant fungi species detected were Penicillium (16.7%) and Aspergillus (12.5%). Conclusions: The findings suggest that this teaching hospital should periodically monitor the air for microorganisms. High-efficiency particulate air filters should be used in areas where those susceptible to infections exist. Appropriate relative humidity levels should be maintained, and the gate-control feature of the ventilation system should be activated to prevent airborne nosocomial infections.