TY - JOUR AU - Riley, Jacob AU - Huntley, Jamie AU - Miller, Jennifer AU - Slaichert, Amelia L.B. AU - Brown, Grant T1 - Mask Effectiveness for Preventing Secondary Cases of COVID-19, Johnson County, Iowa, USA T2 - Emerging Infectious Disease journal PY - 2022 VL - 28 IS - 1 SP - 69 SN - 1080-6059 AB - In September of 2020, the Iowa Department of Public Health released guidance stating that persons exposed to someone with coronavirus disease (COVID-19) need not quarantine if the case-patient and the contact wore face masks at the time of exposure. This guidance differed from that issued by the Centers for Disease Control and Prevention. To determine the best action, we matched exposure information from COVID-19 case investigations with reported test results and calculated the secondary attack rates (SARs) after masked and unmasked exposures. Mask use by both parties reduced the SAR by half, from 25.6% to 12.5%. Longer exposure duration significantly increased SARs. Masks significantly reduced virus transmission when worn by both the case-patient and the contact, but SARs for each group were higher than anticipated. This finding suggests that quarantine after COVID-19 exposure is beneficial even if parties wore masks. KW - 2019 novel coronavirus disease KW - coronavirus disease KW - COVID-19 KW - severe acute respiratory syndrome coronavirus 2 KW - SARS-CoV-2 KW - viruses KW - respiratory infections KW - zoonoses KW - quarantine KW - public health KW - secondary attack rate KW - contact tracing KW - masks KW - Iowa KW - USA DO - 10.3201/eid2801.211591 UR - https://wwwnc.cdc.gov/eid/article/28/1/21-1591_article ER - End of Reference