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Copyright © 2022 The British Infection Association. Published by Elsevier Ltd. All rights reserved. COVID-19 local outbreak response relies on subjective information to reconstruct transmission chains. We assessed the concordance between epidemiologically linked cases and viral genetic profiles, in the Baixo Vouga Region (Portugal), from March to June 2020. A total of 1925 COVID-19 cases were identified, with 1143 being assigned to 154 epiclusters. Viral genomic data was available for 128 cases. Public health authorities identified two large epiclusters (280 and 101 cases each) with a central role on the spread of the disease. Still, the genomic data revealed that each epicluster included two distinct SARS-CoV-2 genetic profiles and thus more than one transmission network. We were able to show that the initial transmission dynamics reconstruction was most likely accurate, but the increasing dimension of the epiclusters and its extension to densely populated settings (healthcare and nursing home settings) triggered the misidentification of links. Genomics was also key to resolve some sporadic cases and misidentified direction of transmission. The epidemiological investigation showed a sensitivity of 70%-86% to detect transmission chains. This study contributes to the understanding of the hurdles and caveats associated with the epidemiological investigation of hundreds of community cases in the context of a massive outbreak caused by a highly transmissible and new respiratory virus. publishersversion published

Background: Ovar was the first Portuguese municipality to declare active community transmission of SARS-CoV-2, with total lockdown decreed on March 17, 2020. This context provided conditions for a large-scale testing strategy, allowing a referral system considering other symptoms besides the ones that were part of the case definition (fever, cough, and dyspnea). This study aims to identify other symptoms associated with COVID-19 since it may clarify the pre-test probability of the occurrence of the disease. Methods: This case-control study uses primary care registers between March 29 and May 10, 2020 in Ovar municipality. Pre-test clinical and exposure-risk characteristics, reported by physicians, were collected through a form, and linked with their laboratory result. Results: The study population included a total of 919 patients, of whom 226 (24.6%) were COVID-19 cases and 693 were negative for SARS-CoV-2. Only 27.1% of the patients reporting contact with a confirmed or suspected case tested positive. In the multivariate analysis, statistical significance was obtained for headaches (OR 0.558), odynophagia (OR 0.273), anosmia (OR 2.360), and other symptoms (OR 2.157). The interaction of anosmia and odynophagia appeared as possibly relevant with a borderline statistically significant OR of 3.375. Conclusion: COVID-19 has a wide range of symptoms. Of the myriad described, the present study highlights anosmia itself and calls for additional studies on the interaction between anosmia and odynophagia. Headaches and odynophagia by themselves are not associated with an increased risk for the disease. These findings may help clinicians in deciding when to test, especially when other diseases with similar symptoms are more prevalent, namely in winter.

From March 17 to April 17, 2020, the Portuguese municipality of Ovar was submitted to a cordon sanitaire due to a COVID-19 outbreak. During this period a whole Public Health structure had to be built up to respond to the healthcare needs of the population. The aim of this work is to contribute to the evidence on the efficacy of cordon sanitaire as an epidemic control strategy.All the major institutions in Ovar, both health and socially related, were called from the first day to form a Crisis Cabinet. Case tracking was assured by the creation of an online database. A major telephone network oversaw contact tracing, isolation mandates and surveillance. A massive testing structure was built up, and clinical assistance was assured by the local hospital and the Primary Care units. Patient referral to testing and clinical visits were made through online forms that allowed an efficient response and data for epidemiologic research.A decline in the daily number of cases was seen after an incubation period (14 days), confirming lockdown was effective in blocking transmission chains. Besides, neighbouring municipalities were not significantly affected in relation to others. Lethality was bigger in Ovar than in whole Portugal.The decrease in the incidence, in the reproductive number and the non-affection of neighbouring municipalities appear to prove the cordon sanitaire as an effective Public Health measure to contain epidemics. However, an appropriate mitigation strategy must be adopted to conceal the challenge.