Bio-aerosols are airborne particles that are living (bacteria, viruses and fungi) or originate from living organisms. Their presence in air is the result of dispersal from a site of colonization or growth. The health effects of bio-aerosols including infectious diseases, acute toxic effects, allergies and cancer coupled with the threat of bioterrorism and SARS have led to increased awareness on the importance of bio-aerosols. The evaluation of bio-aerosols includes use of variety of methods for sampling depending on the concentration of microorganisms expected. There have been problems in developing standard sampling methods, in proving a causal relationship and in establishing threshold limit values for exposures due to the complexity of composition of bio-aerosols, variations in human response to their exposure and difÞ culties in recovering microorganisms. Currently bio-aerosol monitoring in hospitals is carried out for epidemiological investigation of nosocomial infectious diseases, research into airborne microorganism spread and control, monitoring biohazardous procedures and use as a quality control measure. In India there is little awareness regarding the quality of indoor air, mould contamination in indoor environments, potential source for transmission of nosocomial infections in health care facilities. There is an urgent need to undertake study of indoor air, to generate baseline data and explore the link to nosocomial infections. This article is a review on composition, sources, modes of transmission, health effects and sampling methods used for evaluation of bio-aerosols, and also suggests control measures to reduce the loads of bio-aerosols.

Objectives: Study was conducted to assess whether temporal variation exists in airborne microbial concentrations of a hospital ward (west-Chennai, India) using active and passive methods, and characterise the microorganisms. Methods: Air samples (duplicates) were collected simultaneously using exposed-plate, impingement (BioSampler) and filtration (personal sampling filter cassette loaded with gelatin filter) methods over different periods of the year. Bacterial plates were incubated at 37°C and observed for growth after 48h; fungal plates were incubated at 25°C and 37°C and observed upto 7 days. Microorganisms were identified using standard microbiological procedures. Enterobacter and Pseudomonas were the predominant Gram-negative bacilli. Among fungi, Aspergillus niger was isolated throughout the year. There was no significant temporal variation in airborne microbial loads irrespective of methods. Conclusions: Exposed-plate method was found to capture microorganisms efficiently with little variation in duplicate samples, suggesting its use in hospitals for preliminary assessment of indoor air quality and determine pathogenic microorganisms due to particle fall-out.

A 3-month pilot study (February—April 2006) was conducted to determine the quality of indoor air in hospitals in the Tamil Nadu region of India and to characterize the predominant aerobic bacteria and fungi present. The main objectives were (1) to sample the indoor air of three different hospitals in Chennai for bioaerosols to generate baseline data using the Petri plate gravitational settling (passive) method of sampling; and (2) to isolate and identify potentially pathogenic organisms prevalent in the hospital environment. Indoor air samples were collected from various wards at the different hospitals and processed for the identification of various predominant bacteria and fungi. The overall counts of Gram-positive organisms were found to be higher than Gram-negative organisms. Of these isolates, Staphylococci and Micrococci were the predominant Gram-positive bacteria, while Klebsiella sp. and Pseudomonas sp. were the predominant potentially pathogenic Gram-negative bacteria isolated. Among yeasts and molds, Aspergillus niger and A. flavus were commonly isolated.

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