Introduction Bioaerosols and infectious patients in various departments within health facilities can be a risk of airborne infections. Concentration profiles of airborne bacteria including Mycobacterium tuberculosis (MTB) in hospitals have not been well characterised. This study assessed the levels of airborne bacteria and evaluated whether carbon dioxide (CO₂) could be an indicator of airborne bacterial concentration.

Methods A cross-sectional study was conducted at four public sector hospitals in South Africa, two with ultraviolet germicidal irradiation (UVGI) fixtures (A and D) and two without (B and C). Risk areas included respiratory isolation rooms, TB wards, respiratory wards, general medical wards, outpatient consulting rooms and waiting areas. Air samples (n=316, A=106, B=30, C=58, D=122) were collected in the morning and afternoon using the MAS-100 sampler. Personal (4 l/s) and stationary (20 l/s) airborne TB samples were collected and quantified by real-time qPCR. Environmental parameters (temperature, relative humidity (%RH), air velocity and CO₂) were also measured. The data was analysed using Stata version 11.1.

Results The results revealed differences (p<0.05) in air quality within and between hospitals. The average bacterial levels ranged from 20–1380 cfu/m³, with hospital C having the highest average counts (611 cfu/m³) followed by hospital B with 365 cfu/m³. Detectable airborne TB was reported in the waiting area of hospital B. Hospitals with UVGI fixtures had significantly (p=0.0001) lower airborne microbial loads (181 cfu/m³) than those without (528 cfu/m³). The Kruskal Wallis test showed no bacterial count variability over a three day period or between morning and afternoon. A meaningful correlation (r=0.51, p<0.05) was found between airborne microbial levels and CO₂ levels (401–2398 ppm).

Conclusion CO₂ may be a predictor of microbial air quality however low bacterial counts may contain pathogens which may cause infection. Non-TB areas such as waiting areas pose a risk of exposure for health workers.