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.

2020 年 9 月，爱荷华州公共卫生部发布指南，指出如果患者和接触者在接触时佩戴口罩，则接触过冠状病毒病 (COVID-19) 患者的人无需隔离。该指南与疾病控制和预防中心发布的指南不同。为了确定最佳行动，我们将 COVID-19 病例调查的暴露信息与报告的测试结果进行了匹配，并计算了蒙面和未蒙面暴露后的二次攻击率 (SAR)。双方均使用口罩，SAR 值降低了一半，从 25.6% 降至 12.5%。较长的暴露时间会显着增加 SAR。当病例患者和接触者佩戴口罩时，病毒传播显着减少，但各组的 SAR 均高于预期。这一发现表明，即使聚会佩戴口罩，接触 COVID-19 后的隔离也是有益的。