Comparison of culturable airborne bacteria and related environmental factors at underground subway stations between 2006 and 2013

In this study, we evaluated concentrations of culturable airborne bacteria (CAB) from 16 underground subway stations of Seoul Metro, Korea, between 2006 and 2013 to identify influential environmental factors, including the presence of platform screen doors (PSD), temperature, relative humidity, depth of the station, and year of construction. In total, 66 air samples were collected from all stations. Results indicated that CAB concentrations and the number of gram-negative bacteria (GNB) were significantly lower in stations with PSD and in which GNB were not detected than in stations lacking PSD and in which GNB were detected. Although there was no significant difference in CAB concentrations with variations in time, CAB concentrations of stations appeared to alter with time due to variation in the number of passengers in transit; indeed, there was a significant association between CAB concentration and the number of passengers passing through a station. The source of CAB seemed to be the poor air quality in the old subway stations. Therefore, ventilation management should be inspected more regularly, and indoor air quality should be controlled in underground subway stations.