Preprints with The Lancet is part of SSRN´s First Look, a place where journals and other research experts identify content of interest prior to publication. These preprint papers are not peer-reviewed. Authors have either opted in at submission to The Lancet family of journals to post their preprints on Preprints with The Lancet, or submitted directly via SSRN. The usual SSRN checks and a Lancet-specific check for appropriateness and transparency have been applied. Preprints available here are not Lancet publications or necessarily under review with a Lancet journal. These papers should not be used for clinical decision making or reporting of research to a lay audience without indicating that this is preliminary research that has not been peer-reviewed. For more information see the Comment published in The Lancet, or visit The Lancet´s FAQ page, and for any feedback please contact preprints@lancet.com

22 Pages Posted: 31 Mar 2020

Abstract

Background: In December 2019, a newly identified coronavirus (SARS-CoV-2) emerged in Wuhan, China, causing respiratory disease (COVID-19) presenting with fever, cough and frequently pneumonia. WHO has set the strategic objective to interrupt virus spread of SARS-CoV-2 worldwide. An outbreak in Bavaria, Germany, starting end of January 2020, gave the opportunity to study transmission events, incubation period, and attack rates.



Methods: A case was defined as a person with SARS-CoV-2-infection confirmed by PCR. Case interviews were conducted to i) describe timing of onset and nature of symptoms, ii) identify and classify contacts. High-risk contacts were actively followed and monitored for symptoms, low-risk contacts were tested upon self-reporting of symptoms. Whole genome sequencing was used to confirm epidemiological links and clarify transmission events where contact histories were ambiguous; integration with epidemiological data enabled precise reconstruction of exposure events and incubation periods.



Results: Case #0 was a Chinese person who visited Germany for professional reasons. Sixteen subsequent cases emerged in four transmission generations. Signature mutations occurred upon foundation of generation 2, as well as in one patient pertaining to generation 4. Median incubation period and serial interval were 4.0 days, respectively. Transmissions occurred frequently pre-symptomatic, at day of symptom onset and during prodromal phase (symptoms other than fever and cough for ≥1 day at beginning of illness phase). Attack rates were 75% among members of a household cluster in common isolation, 10% among household contacts only together until isolation of case, and 5% among non-household high-risk contacts.



Conclusions: While our cases present with predominately mild, non-specific symptoms, infectiousness before or on the day of symptom onset or during prodromal phase is substantial. Additionally, the incubation period is often very short, false-negative tests may occur. Although the outbreak was apparently controlled, successful long-term and global containment of COVID-19 may be difficult to achieve.



Funding Statement: Contributions by C. D. and V. M. C. were funded by the German Ministry of Health (Konsiliarlabor für Coronaviren), as well as the German Center for Infection Research. S.B., T.W., K.P., N.M, and T.S.B. are fellows of the ECDC Fellowship Programme, supported financially by the European Centre for Disease Prevention and Control (ECDC).



Declaration of Interests: The authors declared no competing interest.



Ethics Approval Statement: The outbreak investigation was conducted as part of the authoritative, official tasks of the county health departments as well as the state health department of the Bavarian Health and Food Safety Authority, supported by the Robert Koch Institute. As conducted in response to a public health emergency, this study was exempt from institutional review board approval.