In a recent study posted to the medRxiv* preprint server, researchers assessed the association between indoor air respiratory pathogens and natural ventilation, carbon dioxide (CO2) levels, and air filtration.

Study: Natural ventilation, low CO2 and air filtration are related to reduced indoor air respiratory pathogens. Image Credit: ART-ur/Shutterstock

Currently, little is thought in regards to the effects of indoor climate, human activity, ventilation, and air filtration on the detection and concentration of respiratory pathogens. The capability to quantify bioaerosols in indoor air to watch respiratory infections and transmission risk is hampered by this lack of understanding and hence requires extensive research.

In regards to the study

In the current study, researchers pinpoint the host, pathogen, behavioral, and environmental variables which are related to the next respiratory pathogen bioaerosol burden in indoor ambient air.

Between October 2021 and April 2022, the team collected 341 ambient air samples at 21 sampling locations. By treating the quantitative polymerase chain response (qPCR) results of every pathogen in a sample as a single commentary, the team examined the independent impacts of a wide range of variables on airborne pathogen detection and concentration. The generated models had within-sample correlation adjustments and included pathogen type as a covariate.

For every pathogen, the team ran a logistic regression model (LRM) with backward elimination using the retained independent variables from these models, which employed qPCR Ct values because the numerical results. For twenty-four days, starting on February 7, air samples were collected concurrently within the three nursery groups. Location 2 had three Blue PURE 221 filters installed, while location 1 had no air filtration, leading to a complete theoretical clean air delivery rate of 1770 m3/hour and 10.7 air changes per hour (ACH). Three Philips 3000i filters were placed at location 3, leading to a complete theoretical clean air delivery rate of 999 m3/hour and 6.1 air changes per hour.

Results

The study results showed that essentially the most prevalent infections discovered when comparing the positivity rates of all samples were Streptococcus pneumoniae, human enterovirus, human bocavirus, human adenovirus, and human cytomegalovirus, in that order. The age range of three to 6 years had the biggest percentage of samples that tested positive for not less than one pathogen, followed by zero to 3 years, 25 to 65 years, 12 to 18 years, 18 to 25 years, six to 12 years, and greater than 65 years.

Within the nursery environment depicted, human bocavirus, human enterovirus, human cytomegalovirus, and Streptococcus pneumoniae were nearly at all times positive. Over the winter, the team noticed an extended rise in human adenovirus and Pneumocystis jirovecii infections. Other viruses, akin to enterovirus D68, influenza A virus, human parainfluenza virus 3, respiratory syncytial virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Human CoV 229E, human CoV HKU-1, human CoV OC43, enterovirus D68 exhibited shorter peaks. Variations in positive results for SARS-CoV-2, enterovirus D68, and influenza A virus matched findings from clinical samples in University Hospitals Leuven, situated near the sampling site.

Before grouping, 14 pathogens had not less than 10 positive results, and 12 pathogens had not less than 10 positive results. First, a LRM binary consequence for any respiratory pathogen positivity was used. Pathogen detection was shown to be inversely correlated with vocalization. Every 100 ppm increase in CO2 concentration raised the likelihood of finding a respiratory infection by 8.8%. As natural ventilation increased regularly, odds reduced by 11%. The generalized estimating equations (GEE) models and mixed logistic regression model (MLRM) that account for within-sample correlation each had equal significance levels and effect sizes.

As a result of the smaller sample numbers, the ability of those models was reduced. Nonetheless, they still showed a big correlation between mean CO2 and the detection of human enterovirus, other CoVs, Pneumocystis jiroveci, and Streptococcus pneumoniae. Then again, the team discovered a negative correlation with the invention of human bocavirus. Moreover, natural ventilation negatively correlated with the presence of respiratory syncytial virus and Pneumocystis jiroveci.

The qPCR Ct value declined by 0.13 for every 100 ppm rise in CO2. In contrast to the sooner analyses, natural ventilation was not substantially linked to concentration. Nonetheless, there was a 0.57 increase in average Ct when air filtering was present, which was substantially linked with pathogen concentration. Also, performing an MLRM and when removing imputed values, significance levels and effect sizes were comparable.

The next concentration of human adenovirus, human cytomegalovirus, human bocavirus, and Streptococcus pneumoniae remained favorably correlated with mean CO2. The respiratory syncytial virus was related to a lower concentration. Human bocavirus, human cytomegalovirus, various coronaviruses, and Streptococcus pneumoniae were all present in reduced amounts within the air after air filtration.

Conclusion

The study findings showed that the variety of detected pathogens and their corresponding concentrations varied dramatically depending on the pathogen, month, and age group. Notably, low natural ventilation and high CO2 were independent risk aspects for detection. Their concentration was independently correlated with each CO2 concentration and air filtration. The researchers supported the usage of air filtration and ventilation in reducing pathogen transmission.

*Essential notice

medRxiv publishes preliminary scientific reports that should not peer-reviewed and, due to this fact, shouldn’t be thought to be conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:

• Joren Raymenants, Caspar Geenen, Lore Budts, Jonathan Thibaut, Marijn Thijssen, Hannelore De Mulder, Sarah Gorissen, Bastiaan Craessaerts, Lies Laenen, Kurt Beuselinck, Sien Ombelet, Els Keyaerts, Emmanuel Andre. (2022). Natural ventilation, low CO2 and air filtration are related to reduced indoor air respiratory pathogens. medRxiv. doi: https://doi.org/10.1101/2022.09.23.22280263 https://www.medrxiv.org/content/10.1101/2022.09.23.22280263v1