Standard contact tracing practice for COVID-19 is to identify persons exposed to an infected person during the contagious period, assumed to start two days before symptom onset or diagnosis. In the first large cohort study on backward contact tracing for COVID-19, we extended the contact tracing window by 5 days, aiming to identify the source of the infection and persons infected by the same source. The risk of infection amongst these additional contacts was similar to contacts exposed during the standard tracing window and significantly higher than symptomatic individuals in a control group, leading to 42% more cases identified as direct contacts of an index case. Compared to standard practice, backward traced contacts required fewer tests and shorter quarantine. However, they were identified later in their infectious cycle if infected. Our results support implementing backward contact tracing when rigorous suppression of viral transmission is warranted.
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.
Wastewater surveillance plays an important role in the management of the coronavirus disease 2019 (COVID‐19) pandemic all over the world. Using different wastewater collection points in Leuven, we wanted to investigate the use of wastewater surveillance as an early warning system for an uprise of infections and as a tool to follow the circulation of specific variants of concern (VOCs) in particular geographic areas. Wastewater samples were collected from local neighborhood sewers and from a large regional wastewater treatment plant (WWTP) in the area of Leuven, Belgium. After virus concentration, severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) RNA was quantified by real‐time quantitative polymerase chain reaction (RT‐qPCR) and normalized with the human fecal indicator pepper mild mottle virus (PMMoV). A combination of multiplex RT‐qPCR assays was used to detect signature mutations of circulating VOCs. Fecal virus shedding of SARS‐CoV‐2 variants was measured in feces samples of hospitalized patients. In two residential sampling sites, a rise in wastewater SARS‐CoV‐2 concentration preceded peaks in positive cases. In the WWTP, viral load peaks were seen concomitant with the consecutive waves of positive cases caused by the original Wuhan SARS‐CoV‐2 strain and subsequent VOCs. During the Omicron BA.1 wave, the wastewater viral load increased to a lesser degree, even after normalization of SARS‐CoV‐2 concentration using PMMoV. This might be attributable to a lower level of fecal excretion of this variant. Circulation of SARS‐CoV‐2 VOCs Alpha, Delta, Omicron BA1/BA.2, and BA.4/BA.5 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. Wastewater‐based surveillance is a sensitive tool to monitor SARS‐CoV‐2 circulation levels and VOCs in larger regions. In times of reduced test capacity, this can prove to be highly valuable. 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.
Currently, the real-life impact of indoor climate, human behaviour, 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 in Belgium 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. Pathogen detection and concentration varied significantly by pathogen, month, and age group in generalised linear (mixed) models and generalised estimating equations. High CO2 and low natural ventilation were independent risk factors for detection. The odds ratio for detection was 1.09 (95% CI 1.03–1.15) per 100 parts per million (ppm) increase in CO2, and 0.88 (95% CI 0.80–0.97) per stepwise increase in natural ventilation (on a Likert scale). CO2 concentration and portable air filtration were independently associated with pathogen concentration. Each 100ppm increase in CO2 was associated with a qPCR Ct value decrease of 0.08 (95% CI −0.12 to −0.04), and portable air filtration with a 0.58 (95% CI 0.25–0.91) increase. The effects of occupancy, sampling duration, mask wearing, vocalisation, temperature, humidity and mechanical ventilation were not significant. Our results support the importance of ventilation and air filtration to reduce transmission.
Testing and contact tracing are standard tools for controlling the spread of COVID-191. Their effectiveness hinges on a sequence of processes encompassing testing coverage and timeliness, testing quality and speed of reporting, contact tracing speed and comprehensiveness and compliance with advice given2–6. We optimized this sequence of processes in the context of a public health program targeting around 33,000 higher education students through a combination of low barrier PCR testing with rapid turn-around-time, close integration of testing and tracing teams and IT infrastructure, community engagement and the implementation of bidirectional contact tracing by extending the contact tracing window from 2 to 7 days before symptom onset or test of the index case. We anticipate this combined intervention to help improve epidemic control.
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