Levels of Indoor Airborne Microbes Associated with Ventilation Efficiency in Naturally-Ventilated Residences

Indoor microbial exposure has been implicated in various adverse health effects. This study aimed toexamine the effects of ventilation efficiency on indoor/outdoor (I/O) levels of airborne microbes in homes with natural ventilation, a predominant type adopted by most residential buildings in Taiwan where high microbial concentrations have been reported. Environmental investigations were conducted in 44 homes. Indoor and outdoor airborne bacteria and fungi were collected using a Burkard sampler with Trypticase Soy agar and Malt Extract agar in a flow rate of 10 L/min. Air change rate (AC/H) was measured using the tracer gas concentration decay method. Indoor airborne bacteria and total fungi levels in most investigated houses were generally greater than 1000 CFU/m3. The most frequently isolated fungal genera were Aspergillus, Penicillium, Cladosporium, Alternaria and Yeast. Only the I/O ratios of A. niger and Penicillium were significantly higher for those homes with an air change rate of less than 2.13 /h, the median value, comparedto those with greater than 2.13 (p