Mongkolsuk, S. | bioRxiv Science

bioRxiv2021

Effects of face masks and ventilation on the risk of SARS-CoV-2 respiratory transmission in public toilets: a quantitative microbial risk assessment

Public toilets could increase the risk of COVID-19 infection via airborne transmission; however, related research is limited. We aimed to estimate SARS-CoV-2 infection risk through respiratory transmission using a quantitative microbial risk assessment framework by retrieving SARS-CoV-2 concentrations from the swab tests of 251 Thai patients. Three virus-generating scenarios were investigated: an infector breathing, breathing with a cough, and breathing with a sneeze. Infection risk (97.5th percentile) was as high as 10-3 with breathing and increased to 10-1 with a cough or sneeze, thus all higher than the risk benchmark of 5 x 10-5 per event. No significant gender differences for toilet users (receptors) were noted. The highest risk scenario of breathing and a sneeze was further evaluated for risk mitigation measures. Risk mitigation to lower than the benchmark succeeded only when the infector and receptor simultaneously wore an N95 respirator or surgical mask and when the receptor wore an N95 respirator and the infector wore a denim fabric mask. Ventilation up to 20 air changes per hour (ACH), beyond the 12-ACH suggested by the WHO, did not mitigate risk. Virus concentration, volume of expelled droplets, and receptor dwell time were identified as the main contributors to transmission risk. Highlights- The use of public toilets poses a risk of SARS-CoV-2 respiratory transmission - Highest risks generated in the order of sneezing, coughing, and breathing - No gender differences in risk by counteracting dwell times and inhalation rates - Ventilation did not reduce risk even at 20 ACH, beyond the WHO-recommended value - N95 and surgical masks offer the most effective risk mitigation to toilet users Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=141 SRC="FIGDIR/small/457245v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@e25795org.highwire.dtl.DTLVardef@1e429eaorg.highwire.dtl.DTLVardef@7c002aorg.highwire.dtl.DTLVardef@ef001e_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2020

Superior performance of human wastewater-associated viral markers compared to bacterial markers in tropical environments

Identifying human sewage contamination via microbial source tracking (MST) marker genes has proven useful for effective water quality management worldwide; however, performance evaluations for these genes in tropical areas are limited. Therefore, this research assessed four human-associated MST marker genes in aquatic environments of Central Thailand: human polyomaviruses (JC and BK viruses [HPyVs]), bacteriophage crAssphage (CPQ_056), Lachnospiraceae Lachno3, and Bacteroides BacV6-21. HPyV and crAssphage assays were highly sensitive and specific to sewage (n = 19), with no cross-detection in 120 swine, cattle, chicken, duck, goat, sheep, and buffalo composite fecal samples. Lachno3 and BacV6-21 demonstrated high sensitivity but moderate specificity; however, using both markers could improve specificity to >0.80 (max value of 1.00). The most abundant markers in sewage were Lachno3 and BacV6-21 (5.42-8.02 and non-detected-8.05 log10 copies/100 mL), crAssphage (5.28-7.38 log10 copies/100 mL), and HPyVs (3.66-6.53 log10 copies/100 mL), respectively. HPyVs showed higher levels (up to 4.33 log10 copies/100 mL) and higher detection rates (92.7%) in two coastal beaches (n = 41) than crAssphage (up to 3.51 log10 copies/100 mL and 56.1%). HPyVs were also found at slightly lower levels (up to 5.10 log10 copies/100 mL), but at higher detection rates (92.6%), in a freshwater canal (n = 27) than crAssphage (up to 5.21 log10 copies/100 mL and 88.9%). Overall, both HPyVs and crAssphage are suggested as human sewage-associated MST markers in aquatic environments of Central Thailand. This study underlines the importance of characterizing and validating MST markers in host groups and environmental waters before including them in a water quality management toolbox.

microbiology↗