ABSTRACT
During the COVID-19 pandemic, wastewater-based epidemiology (WBE) has been engaged to complement medical surveillance and in some cases to also act as an early diagnosis indicator of viral spreading in the community. Most efforts worldwide by the scientific community and commercial companies focus on the formulation of protocols for SARS CoV-2 analysis in wastewater and approaches addressing the quantitative relationship between WBE and medical surveillance are lacking. In the present study, a mathematical model is developed which uses as input the number of daily positive medical tests together with the highly non-linear shedding rate curve of individuals to estimate the evolution of virus shedding rate in wastewater along calendar days. A comprehensive parametric study by the model using as input actual medical surveillance and WBE data for the city of Thessaloniki ([~]700,000 inhabitants, North Greece) during the outbreak of November 2020 reveals the conditions under which WBE can be used as an early warning tool for predicting pandemic outbreaks. It is shown that early warning capacity is different along the days of an outbreak and depends strongly on the number of days apart between the day of maximum shedding rate of infected individuals in their disease cycle and the day of their medical testing. The present data indicate for Thessaloniki an average early warning capacity of around 2 days. Moreover, the data imply that there exists a proportion between unreported cases (asymptomatic persons with mild symptoms that do not seek medical advice) and reported cases. The proportion increases with the number of reported cases. The early detection capacity of WBE improves substantially in the presence of an increasing number of unreported cases. For Thessaloniki at the peak of the pandemic in mid-November 2020, the number of unreported cases reached a maximum around 4 times the number of reported cases. HIGHLIGHTSO_LIModel estimates viral load evolution in wastewater from infected people dynamics C_LIO_LIIdentifying actual conditions for which WBE can be used as an early warning tool C_LIO_LIEarly warning capacity increases with an increasing number of unreported cases C_LIO_LIIn Thessaloniki Nov20 outbreak, the early warning capacity of WBE was about 2 days C_LIO_LIIn Thessaloniki Nov20 outbreak, unreported cases were up to 4 times reported cases C_LI
ABSTRACT
Molecular epidemiology has provided an additive value to traditional public health tools by identifying SARS-CoV-2 clusters, or providing evidence that clusters based on virus sequences and contact tracing are highly concordant. Our aim was to infer the levels of virus importation and to estimate the impact of public health measures related to travel restrictions to local transmission in Greece. Our phylogenetic and phylogeographic analyses included 389 SARS-CoV-2 sequences collected during the first 7 months of the pandemic in Greece and a random collection in 5 replicates of 3,000 sequences sampled globally, as well as the best hits to our dataset identified by BLAST. Phylogenetic analyses revealed the presence of 70 genetically distinct viruses identified as independent introductions into Greece. The proportion of imported strains was 41%, 11.5%, and 8.8% during the three periods of sampling, namely, March (no travel restrictions), April to June (strict travel restrictions), and July to September (lifting of travel restrictions based on a thorough risk assessment), respectively. These findings reveal low levels of onward transmission from imported cases during summer and underscore the importance of targeted public health measures that can increase the safety of international travel during a pandemic.
ABSTRACT
We sought to estimate the ascertainment ratio of SARS-CoV-2 infection in Wuhan, China, using a modified Bayesian SEIR model with publicly reported case data. We estimated it at 0.465% (95%CI: 0.464-0.466%), implying that the outbreak in Wuhan was abated by depletion of susceptibles, rather than public health action alone. This suggests a high-transmissibility/low-severity profile for the current pandemic and raises doubt about whether suppression, rather than mitigation, is a feasible goal.
