RESUMO
Currently, the real-life impact of indoor climate, human behavior, ventilation and air filtration on respiratory pathogen detection and concentration are poorly understood. This hinders the interpretability of bioaerosol quantification in indoor air to surveil respiratory pathogens and transmission risk. We tested 341 indoor air samples from 21 community settings for 29 respiratory pathogens using qPCR. On average, 3.9 pathogens were positive per sample and 85.3% of samples tested positive for at least one. The number of detected pathogens and their respective concentrations varied significantly by pathogen, month, and age group in generalized linear (mixed) models and generalized estimating equations. High CO2 and low natural ventilation were independent risk factors for detection. CO2 concentration and air filtration were independently associated with their concentration. Occupancy, sampling time, mask wearing, vocalization, temperature, humidity and mechanical ventilation were not significant. Our results support the importance of ventilation and air filtration to reduce transmission.
RESUMO
To investigate whether wastewater surveillance can be used as an early warning system to detect a rise in SARS-CoV-2 positive cases, and to follow the circulation of specific variants of concern (VOC) in particular geographical areas, wastewater samples were collected from local neighborhood sewers and from a large regional wastewater treatment plant (WWTP) in the area of Leuven, Belgium. In two residential sampling sites, a rise in viral SARS-CoV-2 copies in wastewater preceded the peaks in positive cases. In the WWTP, peaks in the wastewater viral load were seen simultaneous with the waves op positive cases caused by the original Wuhan SARS-CoV-2 strain, the Alpha variant and the Delta variant. For the Omicron BA.1 variant associated wave, the viral load in wastewater increased to a lesser degree, and much later than the increase in positive cases, which could be attributed to a lower level of fecal excretion, as measured in hospitalized patients. Circulation of SARS-CoV-2 VOCs (Alpha, Delta and Omicron) could be detected based on the presence of specific key mutations. The shift in variants was noticeable in the wastewater, with key mutations of two different variants being present simultaneously during the transition period. We found that wastewater based surveillance is a sensitive tool to monitor SARS-CoV-2 circulation levels and VOCs in larger regions. This can prove to be highly valuable in times of reducing testing capacity. Differences in excretion levels of various SARS-CoV-2 variants should however be taken into account when using wastewater surveillance to monitor SARS-CoV-2 circulation levels in the population.
RESUMO
BackgroundStudent residences are at high risk for rapid COVID-transmission due to crowding and frequent close contact. AimWe aimed to investigate the overall secondary attack rates (SAR) in student residences and to discern risk factors for higher transmission in order to improve the evidence base for screening efforts and preventive measures. MethodsIn this retrospective case-ascertained study, we analysed data from student residences screened in Leuven, Belgium between October 2020 and May 2021, following detection of a COVID-19 case in the residence. We investigated the impact on the SAR in the living units screened of delay-time until follow-up, shared use of kitchen or sanitary facilities, presence of an external infection source and occurrence of social gatherings attended by the index case. ResultsWe included 200 residence units, representing 2326 screened residents, of which 68 units showed secondary transmission. The overall SAR was estimated at 0.0813 (95%CI 0.0705-0.0936). Both sharing sanitary facilities (p=0.04) and social gatherings attended by the index case (p=0.033) significantly impacted SAR, which increased from 3% to 13% when both risk factors were present compared to absent. ConclusionsWe identify risk factors which should be considered when selecting students for screening during an outbreak of COVID-19 in student residences to improve comprehensiveness and proportionality of testing. The identified risk factors improve the evidence base for preventive measures aimed at limiting social gatherings and improving ventilation of shared spaces in outbreak-prone settings. Lastly, they should be considered when designing student accommodation and other shared households.
