11/27—Sources of biases in epidemiologic studies of SARS-CoV-2

How to detect and reduce potential sources of biases in epidemiologic studies of SARS-CoV-2
Preprint with Marc Lipsitch, a leading Harvard epidemiologist. Observational studies are subject to a number of different biases, including confounding, selection bias, and measurement error, that may threaten their validity or influence the interpretation of their results. We consider potential biases that could occur in five categories of studies: (1) cross-sectional seroprevalence, (2) longitudinal seroprotection, (3) risk factor studies to inform interventions, (4) studies to estimate the secondary attack rate, and (5) studies that use secondary attack rates to make inferences about infectiousness and susceptibility.

Different Transmission Dynamics of COVID-19 and Influenza Suggest the Relative Efficiency of Isolation/Quarantine and Social Distancing Against COVID-19 in China
In this study, surveillance data of COVID-19 and seasonal influenza in 2018–2020 were used to quantify the relative efficiency of NPIs against COVID-19 in China, since isolation/quarantine was not used for the influenza epidemics. Though isolation/quarantine is more effective than social distancing, given that the typical basic reproductive number of COVID-19 is 2–3, isolation/quarantine alone could not contain the COVID-19 pandemic effectively in China.

Mass gathering events and undetected transmission of SARS-CoV-2 in vulnerable populations leading to an outbreak with high case fatality ratio in the district of Tirschenreuth, Germany
In early March 2020, a COVID-19-outbreak occurred in the district of Tirschenreuth, Germany. The outbreak was characterised by a rapid increase in case numbers and a comparatively high crude case fatality ratio (CFR; 11%). Until the beginning of May 2020, 1122 cases were reported in the district. We found that returning ski-travellers from Austria and Italy and early undetected community transmission likely initiated the outbreak which was then accelerated by Bavarian beer festivities.

COVID-19 in seniors: Findings and lessons from mass screening in a nursing home
Eighty-seven frail older residents (87.9 ± 7.2years; 71 % female) and 92 staff members (38.3 ± 11.7years; 89 % female) were included. The attack rate of COVID-19 was 47 % in residents (case fatality rate, 27 %), and 24 % in staff. The classification tree revealed 100 % COVID-19 probability in the following groups: i) residents younger than 90 with dyspnea and falls; ii) residents older than 90 with anorexia; iii) residents older than 90 without anorexia but with altered consciousness. Finally, 41 % of staff members diagnosed with COVID-19 were asymptomatic. The pauci-symptomatic expression of COVID-19 in older residents, together with the high prevalence of asymptomatic forms in caregivers, justifies mass screening in nursing homes.

Associations between restrictions on public mobility and slowing of new COVID‐19 case rates in three countries
We analysed Google COVID‐19 community mobility data. Three distinct patterns of societal reaction to social restrictions, causing different degrees of economic shutdown, can be differentiated: near complete lockdown (Australia), relaxed lockdown with preserved workplace activity (Sweden), and minimal lockdown with preservation of both workplace and commercial activity (South Korea). Early social restrictions reduced the spread of COVID‐19 in all three countries, as indicated by increased infection doubling times within 14 days of measurable changes in public mobility.

The dark blue lines depict mobility curves based on inflection points identified by automated change point detection using time series analysis; the light blue lines depict the mean lines for the mobility data estimator used for predicting inflection points; the shaded regions indicate uncertainty in the mobility data estimator (two standard deviations around mean line); the dashed vertical lines indicate inflection points of statistical significance.

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