Predictors of incident viral symptoms ascertained in the era of COVID-19
Prospective survey based study with 14,335 participants, showing lower risk of viral symptoms with regular exercise.
risk of symptomatic case, 42.1% lower, RR 0.58, p < 0.001, high activity levels 240 of 10,627 (2.3%), low activity levels 134 of 3,708 (3.6%), NNT 74, adjusted per study, odds ratio converted to relative risk, multivariable.
Effect extraction follows pre-specified rules prioritizing more serious outcomes. Submit updates
Marcus et al., 17 Jun 2021, prospective, multiple countries, peer-reviewed, survey, 12 authors, study period 26 March, 2020 - 3 May, 2020.
Abstract: PLOS ONE
Predictors of incident viral symptoms
ascertained in the era of COVID-19
Gregory M. Marcus ID*, Jeffrey E. Olgin, Noah D. Peyser, Eric Vittinghoff ID, Vivian Yang,
Sean Joyce, Robert Avram ID, Geoffrey H. Tison, David Wen ID, Xochitl Butcher,
Helena Eitel, Mark J. Pletcher
Division of Cardiology, Department of Medicine, University of California, San Francisco, California, United
States of America
Citation: Marcus GM, Olgin JE, Peyser ND,
Vittinghoff E, Yang V, Joyce S, et al. (2021)
Predictors of incident viral symptoms ascertained
in the era of COVID-19. PLoS ONE 16(6):
Editor: Antonio Palazón-Bru, Universidad Miguel
Hernandez de Elche, SPAIN
Received: September 4, 2020
Accepted: May 31, 2021
In the absence of universal testing, effective therapies, or vaccines, identifying risk factors
for viral infection, particularly readily modifiable exposures and behaviors, is required to
identify effective strategies against viral infection and transmission.
We conducted a world-wide mobile application-based prospective cohort study available
to English speaking adults with a smartphone. We collected self-reported characteristics,
exposures, and behaviors, as well as smartphone-based geolocation data. Our main
outcome was incident symptoms of viral infection, defined as fevers and chills plus one
other symptom previously shown to occur with SARS-CoV-2 infection, determined by
Published: June 17, 2021
Copyright: © 2021 Marcus et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: All relevant data are
within the manuscript and its Supporting
Funding: Drs. GM, JO, and MP received funding
from awards IU2CEB021881-01 and
3U2CEB021881-05S1 from the NIH/ NIBIB (https://
www.nibib.nih.gov/). The funders had no role in
study design, data collection and analysis, decision
to publish, or preparation of the manuscript.
Competing interests: The authors have declared
that no competing interests exist.
Among 14, 335 participants residing in all 50 US states and 93 different countries followed
for a median 21 days (IQR 10–26 days), 424 (3%) developed incident viral symptoms. In
pooled multivariable logistic regression models, female biological sex (odds ratio [OR]
1.75, 95% CI 1.39–2.20, p<0.001), anemia (OR 1.45, 95% CI 1.16–1.81, p = 0.001),
hypertension (OR 1.35, 95% CI 1.08–1.68, p = 0.007), cigarette smoking in the last 30
days (OR 1.86, 95% CI 1.35–2.55, p<0.001), any viral symptoms among household members 6–12 days prior (OR 2.06, 95% CI 1.67–2.55, p<0.001), and the maximum number of
individuals the participant interacted with within 6 feet in the past 6–12 days (OR 1.15,
95% CI 1.06–1.25, p<0.001) were each associated with a higher risk of developing viral
symptoms. Conversely, a higher subjective social status (OR 0.87, 95% CI 0.83–0.93,
p<0.001), at least weekly exercise (OR 0.57, 95% CI 0.47–0.70, p<0.001), and sanitizing
one’s phone (OR 0.79, 95% CI 0.63–0.99, p = 0.037) were each associated with a lower
risk of developing viral symptoms.
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