Ventilation in buildings has emerged as a key strategy to reduce exposure to SARS-CoV-2. The virus tends to persist at higher concentrations indoors compared to outdoors, leading to greater risk of transmission while indoors. This can be mitigated by improving air flow in buildings through installing mechanical ventilation systems or by ensuring adequate natural ventilation.
Mechanical ventilation is often unavailable in resource-poor settings, including communal wards housing multiple patients, but it is unclear whether natural ventilation in these spaces circulates air at the rates recommended for minimizing risk of exposure to the virus. Working alongside collaborators from Stanford and the University of California, Berkeley, icddr,b scientists investigated ventilation rates and presence of SARS-CoV-2 in 86 distinct spaces across nine hospitals in Dhaka, Bangladesh.
Ventilation depends not only on how the dimensions and connectivity of a space influence air exchange, but also on the density of people occupying the space. The authors measured ventilation rates in the healthcare spaces using a handheld carbon dioxide meter while taking into account the number of patients occupying each space. Ventilation rates were lower than WHO-recommendation standards in 78.7% of naturally ventilated spaces, indicating consistently poor air circulation and suboptimal mitigation of viral exposure.
The authors also collected air samples from the healthcare spaces to detect the actual presence of SARS-CoV-2 viral particles and discovered that non-COVID spaces were more likely to contain the virus than COVID-designated areas. This may be partially explained by the fact that fewer patients are housed in COVID-designated areas, leading to marginally improved ventilation. The authors also note that healthcare staff were less likely to adhere to recommended PPE usage in non-COVID areas, possibly due to lower perceived risk of exposure. Across samples from 11 non-COVID outpatient areas and open wards, five contained SARS-CoV-2, pointing to not only a need for improved ventilation but also for increased testing and surveillance. The air samples also revealed that mechanically ventilated spaces were less likely to contain SARS-CoV-2 particles than the naturally ventilated spaces.
Vaccines have been successful in reducing the burden of SARS-CoV-2. But non-pharmaceutical interventions such as masks and ventilation remain key in controlling transmission of the virus, and the results of this study show that Bangladeshi hospitals are not optimally reducing risk of transmission by using appropriate ventilation systems or strategies. Many such interventions are not technologically advanced or difficult to implement.
“Measures to improve ventilation in naturally-ventilated healthcare spaces include opening windows and doors to the fullest extent possible, installing window exhaust fans to improve air flow, and limiting the number of people in a given space.” notes the co-author of the paper and Assistant Scientist of icddrb, Dr Badrul Amin, on behalf of the study team.
Vaccines are not universally available — many developing countries remain under vaccinated and unboosted — and tend to be less effective in elderly and immunocompromised individuals even when they are. The current vaccines may also be relatively less effective against newly emerging variants of SARS-CoV-2. Given this context and with COVID-19 cases continuing to surge, it is imperative that we consider implementing effective non-pharmaceutical public health measures, including ventilation enhancements, to mitigate risk and reduce disease burden.