Relationship Between Indoor Air-Quality Parameters and Airborne Microorganisms in Hospital Settings: An Updated Systematic Review and Meta-Analysis

The objective of this study was to evaluate the microbiological profile and indoor air quality in hospital settings through an updated systematic review and meta-analysis of evidence published between 2020 and 2026, quantifying the impact of physical environmental parameters, temperature, relative humidity, carbon dioxide (CO2), and particulate matter, on the microbial load. A systematic search following PRISMA guidelines was conducted across Scopus, Embase, Web of Science, and BVS. Of 1972 initial records, 14 studies met the eligibility criteria and were included in the systematic review, and of these, 13 studies (1012 samples) provided quantitative data suitable for the meta-analysis. Meta-analyses of means and correlations were performed using random-effects models in R. Overall bacterial load averaged 679.52 ± 116.4 CFU/m3. Wards exhibited the highest contamination (1282.67 ± 189.8 CFU/m3), while ICUs recorded lower levels (201.49 ± 74.6 CFU/m3). HEPA filters demonstrated the greatest effectiveness, maintaining bacterial load at 61.31 ± 9.5 CFU/m3, in contrast to naturally ventilated areas (1154.51 ± 142.2 CFU/m3). Fungal load averaged 286.20 ± 123.5 CFU/m3, with HEPA filters maintaining levels at 95.26 ± 16.9 CFU/m3 compared to 438.24 ± 185.8 CFU/m3 in naturally ventilated settings. Relative humidity showed the strongest correlations, with a moderate positive correlation for bacteria (r = 0.59) and a strong positive correlation for fungi (r = 0.62). Particulate matter (PM > 5 µm) also showed a positive correlation with bacteria (r = 0.26), while CO2 exhibited a very strong association with bacteria (r = 0.82). Temperature showed weak correlations with both bacteria and fungi. Hospital aerobiology is governed by a dynamic interaction between ventilation infrastructure and occupancy. Strict control of relative humidity and the maintenance of HEPA filtration in critical areas may contribute to reducing airborne microbial load; direct inferences about infection risk require further prospective studies associated with bioaerosols, particularly in critical areas.