Assessing impact of ventilation on airborne transmission of SARS-CoV-2: a cross-sectional analysis of naturally ventilated healthcare settings in Bangladesh
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Abstract
To evaluate the risk of exposure to SARS-CoV-2 in naturally ventilated hospital settings by measuring parameters of ventilation and comparing these findings with results of bioaerosol sampling.
Study design
Cross-sectional study.
Study setting and study sample
The study sample included nine hospitals in Dhaka, Bangladesh. Ventilation characteristics and air samples were collected from 86 healthcare spaces during October 2020 to February 2021.
Primary outcome
Risk of cumulative SARS-CoV-2 infection by type of healthcare area.
Secondary outcomes
Ventilation rates by healthcare space; risk of airborne detection of SARS-CoV-2 across healthcare spaces; impact of room characteristics on absolute ventilation; SARS-CoV-2 detection by naturally ventilated versus mechanically ventilated spaces.
Results
The majority (78.7%) of naturally ventilated patient care rooms had ventilation rates that fell short of the recommended ventilation rate of 60 L/s/p. Using a modified Wells-Riley equation and local COVID-19 case numbers, we found that over a 40-hour exposure period, outpatient departments posed the highest median risk for infection (7.7%). SARS-CoV-2 RNA was most frequently detected in air samples from non-COVID wards (50.0%) followed by outpatient departments (42.9%). Naturally ventilated spaces (22.6%) had higher rates of SARS-CoV-2 detection compared with mechanically ventilated spaces (8.3%), though the difference was not statistically significant (p=0.128). In multivariable linear regression with calculated elasticity, open door area and cross-ventilation were found to have a significant impact on ventilation.
Conclusion
Our findings provide evidence that naturally ventilated healthcare settings may pose a high risk for exposure to SARS-CoV-2, particularly among non-COVID-designated spaces, but improving parameters of ventilation can mitigate this risk.
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SciScore for 10.1101/2021.06.30.21258984: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
NIH rigor criteria are not applicable to paper type.Table 2: Resources
No key resources detected.
Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:In contrast, four other studies failed to detect SARS-CoV-2 RNA in mechanically-ventilated healthcare spaces despite obtaining substantially larger volumes of filtered air and placing air samplers proximal to infected patients.[43–46] We also did not detect SARS-CoV-2 in bathrooms or PPE doffing rooms, contrasting with other studies that …
SciScore for 10.1101/2021.06.30.21258984: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
NIH rigor criteria are not applicable to paper type.Table 2: Resources
No key resources detected.
Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:In contrast, four other studies failed to detect SARS-CoV-2 RNA in mechanically-ventilated healthcare spaces despite obtaining substantially larger volumes of filtered air and placing air samplers proximal to infected patients.[43–46] We also did not detect SARS-CoV-2 in bathrooms or PPE doffing rooms, contrasting with other studies that found these to be high-risk areas, indicating that risk in these spaces may be context dependent.[47] Of the samples in which we detected SARS-CoV-2 RNA, the median copy number was less than 1 copy/L of air sampled, which is comparable to other studies where SARS-CoV-2 RNA was detected in air samples from healthcare settings.[10–14,48] Given that previous estimates have suggested an infectious dose of SARS-CoV-2 may be in the range of 100-300 virions,[49,50] this could indicate the risk from aerosol transmission may be substantial, especially given that cumulative exposure may be more important for establishing infection than exposure at a single time point.[51] However, it is difficult to translate results of air sample collection to exposure to infectious quanta given limitations of the sample collection process. A unique aspect of this study is an investigation of which parameters of ventilation have the greatest impact on air exchange in naturally-ventilated settings and subsequently how risk was modified by these factors. Ceiling height was found to be the most influential parameter in the elasticity analysis, which has been previously d...
Results from TrialIdentifier: No clinical trial numbers were referenced.
Results from Barzooka: We did not find any issues relating to the usage of bar graphs.
Results from JetFighter: We did not find any issues relating to colormaps.
Results from rtransparent:- Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
- Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
- No protocol registration statement was detected.
Results from scite Reference Check: We found no unreliable references.
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