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. Results: Microbial loads were found to vary with the sampling method. Concentrations of bacteria were higher (exposedplate: 45–150 CFU/plate; impingement: 1.12E+03–1.6856E+05 CFU/m³; filtration: 3.788E+03–1.91111E+05 CFU/m³) than fungi (exposed-plate: 0–13 CFU/plate; impingement: 0–3.547E+03 CFU/m³; filtration: 0–1.515E+04 CFU/m³). Coagulase-negative Staphylococci and Micrococci were the predominant Gram-positive cocci in active and passive samples. 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.

Key words: Indoor air, bioaerosols, hospital ward, tropical setting