Factors that affect the relationship between microorganisms in the air and on surfaces in hospital environments

Hospital acquired infections (HAIs) incur mortalities and high costs for treatment including the ongoing outbreak of the COVID-19 pandemic as a result of contaminated air and surfaces. Understanding the relationship between microorganisms in the air and on surfaces and assessing how hospital environment factors affect this relationship is essential to mitigate the infection risk.
A systematic review and meta-analysis showed that there were positive correlations between the airborne bacteria measured as aerobic colony count (ACC) and indoor air quality (IAQ) parameters in the hospital. Also, previous mathematical approaches to correlating air and surface microorganisms were identified and evaluated against published data.
Environmental sampling was carried out to explore the transient relationships between air and surface bioburden in a hospital. The average concentration of ACC in air was 196±103 cfu.m-3, while our multi-regression model recommended a maximum of 118 cfu.m-3. High touch surfaces in 1-bed, 4-bed, and 10-bed rooms, found 100%, 84%, and 73% surface deposition samples within an accepted level of concentration (<2.5 cfu.cm-2). The loss rate due to deposition onto surfaces (λ_d) was 7.2±2.88h-1 for ACC and 4.32±2.88h-1 for Staphylococcus spp.
The effect of ventilation and spatial location on (λ_d) was investigated by developing and validating a novel Automated Multiplate Passive Air Sampling (AMPAS) device. Increasing the ventilation rate from 3 to 6 ACH results in a reduction of Staphylococcus aureus load in air and on surfaces by 45%±10% and 44%±32%, respectively and λ_d was 1.38±0.48h-1 in the chamber.
The relationship between microorganisms in the air and on surfaces is a significant parameter in an infection risk model. It can be represented by λ_d, however this is complex to determine in a dynamic environment. The findings support the importance of controlling the ventilation and the environmental parameters to mitigate both air and surface infection risks in the hospital environment.