A quantitative and qualitative assessment of microbial populations associated with air-conditioning systems

Abstract

People working in indoor environments often complain of allergies, illness or discomfort. A variety of the symptoms are associated with micro-organisms occurring in these environments. At least some of these micro-organisms originate in or are distributed through the heating, ventilation and air-conditioning (HVAC) systems used in these indoor environments. A study was conducted over a 12-month period, ranging from February 1996 through January 1997, to investigate the microbial populations in selected occupational environments and related respiratory symptoms suffered by occupants of these indoor environments. Based on the type of air-supply system used in the building, four buildings were selected for sampling during the study period. An occupational health questionnaire was compiled to cover a variety of respiratory symptoms related to microbial infections, and was completed by 101 occupants of the four sampled buildings. Certain aspects regarding influenza and hay fever symptoms, as well as a health profile for the 12- month period, were emphasised in the questionnaire. A microbiological study of surrounding air obtained from selected sampling points was conducted to determine the predominance of specific micro-organisms in air-borne infections. The presence of bacteria, moulds and yeasts, as well as species of Pseudomonas were determined. Additionally, water samples were collected from one of the buildings that had a water-based airconditioning system. Water droplets are apparently liberated into the indoor environment by the HVAC system in this building. Micro-organisms could proliferate in the water and affect occupants' health when liberated into the environment. This effect was revealed from the questionnaires. From the questionnaires it emanated that the building occupants suffered from a variety of respiratory-related symptoms, which were more prevalent in certain buildings. As expected, a high incidence of influenza symptoms were observed in the winter months, including blocked or dry noses and gritty eyes. The buildings showed a variation in the numbers of organisms found during the sampling period. Yeasts and moulds were present in all the sampling 'Iocations throughout the sampling period, while Pseudomonas species were not found in any of the buildings. Total bacterial counts were rel atively high at times, especially during the summer months. It was evident that the HVAC systems differ in their effectivity to ensure safe indoor air quality with regards to microbiological pollutants. The comparison of the microbiological data and the health profiles obtained from the questionnaires revealed that micro-organisms found in indoor environments could possibly affect the health of occupants and therefore influence productivity.