Transmission of SARS-COV-2 infections in households — Tennessee and Wisconsin, April–September 2020
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Transmission of SARS-COV-2 infections in households — Tennessee and Wisconsin, April–September 2020

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    What is already known about this topic? Transmission of SARS-CoV-2 occurs within households; however, Transmission estimates vary widely and the data on Transmission from children are limited.

    What is added by this report? Findings from a prospective household study with intensive daily observation for ≥7 consecutive days indicate that Transmission of SARS-CoV-2 among household members was frequent from either children or adults.

    What are the implications for public health practice? Household Transmission of SARS-CoV-2 is common and occurs early after illness onset. Persons should self-isolate immediately at the onset of COVID-like symptoms, at the time of tTesting as a result of a high risk exposure, or at time of a positive test result, whichever comes first. All household members, including the index case, should wear masks within shared spaces in the household.

    mproved understanding of Transmission of SARS-CoV-2, the Virus that causes coronaVirus disease 2019 (COVID-19), within households could aid control measures. However, few studies have systematically characterized the Transmission of SARS-CoV-2 in U.S. households (1). Previously reported Transmission rates vary widely, and data on Transmission rates from children are limited. To assess household Transmission, a case-ascertained study was conducted in Nashville, Tennessee, and Marshfield, Wisconsin, commencing in April 2020. In this study, index patients were defined as the first household members with COVID-19–compatible symptoms who received a positive SARS-CoV-2 reverse transcription–polymerase chain reaction (RT-PCR) test result, and who lived with at least one other household member. After enrollment, index patients and household members were trained remotely by study staff members to complete symptom diaries and obtain self-collected specimens, nasal swabs only or nasal swabs and saliva samples, daily for 14 days. For this Analysis, specimens from the first 7 days were tested for SARS-CoV-2 using CDC RT-PCR protocols.† A total of 191 enrolled household contacts of 101 index patients reported having no symptoms on the day of the associated index patient’s illness onset, and among these 191 contacts, 102 had SARS-CoV-2 detected in either nasal or saliva specimens during follow-up, for a secondary infection rate of 53% (95% confidence interval [CI] = 46%–60%). Among fourteen households in which the index patient was aged <18 years, the secondary infection rate from index patients aged <12 years was 53% (95% CI = 31%–74%) and from index patients aged 12–17 years was 38% (95% CI = 23%–56%). Approximately 75% of secondary infections were identified within 5 days of the index patient’s illness onset, and substantial Transmission occurred whether the index patient was an adult or a child. Because household Transmission of SARS-CoV-2 is common and can occur rapidly after the index patient’s illness onset, persons should self-isolate immediately at the onset of COVID-like symptoms, at the time of tTesting as a result of a high risk exposure, or at the time of a positive test result, whichever comes first. Concurrent to isolation, all members of the household should wear a mask when in shared spaces in the household.§

    The data presented in this report are from an ongoing, CDC-supported study of household Transmission of SARS-CoV-2 in Nashville, Tennessee and Marshfield, Wisconsin, and include households enrolled during April–September 2020.¶ Households were eligible if the index patient had symptom onset <7 days before household enrollment and the household included at least one other person who was not symptomatic at the time of the index patient’s illness onset and was thus deemed to be at risk. Characteristics of the index patients, household members, and their interactions were ascertained using Research Electronic Data Capture (REDCap),** an online application for data collection, or through paper-based surveys. The 7-day secondary infection rate was calculated by dividing the number of laboratory-confirmed SARS-CoV-2 infections identified during the 7-day follow-up period by the number of household members at risk per 100 population.†† Because saliva samples are considered an emerging diagnostic approach but are not yet standard for SARS-CoV-2 detection (2), secondary infection rates were also calculated using positive test results from nasal swab specimens only. To account for household members possibly having been infected when the index case became ill, secondary infections rates were also conservatively calculated excluding household members who had positive test results at enrollment. The study protocol was reviewed and approved by the Vanderbilt University Medical Center’s and Marshfield Clinic Research Institute’s Institutional Review Board, and was conducted consistent with applicable federal law and CDC policy.§§

    Suggested citation for this article: Suggested citation for this article: Grijalva CG, Rolfes MA, Zhu Y, et al. Transmission of SARS-COV-2 Infections in Households — Tennessee and Wisconsin, April–September 2020. MMWR Morb Mortal Wkly Rep. ePub: 30 October 2020.



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