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Volume 28, Number 1—January 2022

Mask Effectiveness for Preventing Secondary Cases of COVID-19, Johnson County, Iowa, USA

Jacob RileyComments to Author , Jamie M. Huntley, Jennifer A. Miller, Amelia L.B. Slaichert, and Grant D. Brown
Author affiliations: Johnson County Public Health, Iowa City, Iowa, USA (J. Riley, J.M. Huntley, J.A. Miller, A.L.B. Slaichert); University of Iowa, Iowa City, Iowa, USA (G.D. Brown)

Main Article

Table 2

Additional variables for study of mask effectiveness for preventing secondary cases of coronavirus disease, Johnson County, Iowa, USA

Variable Negative Positive Secondary attack rate (95% CI), %
Symptomatic 365 100 21.5 (18.1–25.6)
Not symptomatic
20.9 (17.4–25.2)
Exposure duration, h
>2 413 142 25.6 (22.2–29.5)
13.5 (9.6–18.8)
Exposure setting
Indoors 488 107 18 (15.1–21.3)
Outdoors 27 9 25 (14.2–44.0)
Direct exposure 9 5 35.7 (17.7–72.1)
Multiple settings 72 25 25.8 (18.4–36.1)

Main Article

Page created: October 12, 2021
Page updated: December 20, 2021
Page reviewed: December 20, 2021
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.