Assessment of bacterial and fungal bioaerosols in light rail transit (LRT-1) trains in Metro Manila (Philippines)

Abstract

Characterization of indoor bioaerosols, especially in areas frequented by a massive number of people, is of public health significance. This study was performed to assess the bacterial and fungal bioaerosols inside the Light Rail Transit (LRT) trains, which are utilized by a lot of commuters almost on a daily basis. Temporal variations in bioaerosol composition, as well as contributing factors, were evaluated. Air samples were collected using a bioaerosol impactor at six different time periods for three separate days. The number of passengers and meteorological data were determined. Bacterial and fungal species, and their concentrations in the bioaerosol were identified. Micrococcus spp. were the most abundant and frequent species obtained throughout the sampling periods, followed by Bacillus spp. and Staphylococcus epidermidis. Potential agents were detected, including those that are rarely isolated from normal indoor air such as Streptococcus pneumoniae and Enterococcus spp. Important indicator contaminants were also detected such as Actinomycetes, Aspergillus fumigatus and high concentrations of Penicillum spp. The airborne microbial concentrations and the number of passengers were strongly correlated. Microbial concentrations were significantly higher during rush hour periods than in non-rush hour periods. These suggest that people could be the primary source of the LRT train bioaerosol, and as they are also the natural habitat of most of the species identified. Poor heating, ventilation and air conditioning (HVAC) systems may also be potential sources, as microbial concentrations in post-operational periods are significantly higher than in pre-operational periods, implying accumulation of airborne microbiome. Outdoor conditions can be a major driver of the indoor bioaerosol as well, as observed in the variation of fungal composition. Microbial concentrations in three rush hour periods exceeded acceptable levels, which represent increased health risk on the commuters, especially those belonging to vulnerable groups.