In this post I link to and excerpt from the Oct 30, 2020 Morbidity and Mortality Weekly Report, Transmission of SARS-COV-2 Infections in Households — Tennessee and Wisconsin, April–September 2020.
Here are excerpts:
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 testing 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.
In this ongoing prospective study that includes systematic and daily follow-up, transmission of SARS-CoV-2 among household members was common, and secondary infection rates were higher than have been previously reported (1,3–7). Secondary infections occurred rapidly, with approximately 75% of infections identified within 5 days of the index patient’s illness onset. Secondary infection rates were high across all racial/ethnic groups. Substantial transmission occurred whether the index patient was an adult or a child.
Several studies have reported estimates of household transmission, largely from contact tracing activities, with limited follow-up and testing of household members or delayed enrollment relative to index patient identification (3–5,7). These different approaches to ascertain infections could explain the higher secondary infection rates observed in this study relative to other estimates. In addition, other studies, particularly those conducted abroad, might have found lower secondary infection rates because of rapid isolation of patients in facilities outside households or different adoption of control measures, such as mask use, in the home (3–5,7,8).
Because prompt isolation of persons with COVID-19 can reduce household transmission, persons who suspect that they might have COVID-19 should isolate, stay at home, and use a separate bedroom and bathroom if feasible. Isolation should begin before seeking testing and before test results become available because delaying isolation until confirmation of infection could miss an opportunity to reduce transmission to others. Concurrently, all household members, including the index patient, should start wearing a mask in the home, particularly in shared spaces where appropriate distancing is not possible. Close household contacts of the index patient should also self-quarantine, to the extent possible, particularly staying away from those at higher risk of getting severe COVID-19. To complement these measures within the household, a potential approach to reduce SARS-CoV-2 transmission at the community level would involve detecting infections before onset of clinical manifestations; this would require frequent and systematic testing in the community with rapidly available results to enable prompt adoption of preventive measures. The feasibility and practicality of this approach is undergoing extensive discussion (9) and study. This ongoing household transmission study will provide critical data regarding the recommended timing and frequency of testing.
An important finding of this study is that fewer than one half of household members with confirmed SARS-CoV-2 infections reported symptoms at the time infection was first detected, and many reported no symptoms throughout 7 days of follow-up, underscoring the potential for transmission from asymptomatic secondary contacts and the importance of quarantine. Persons aware of recent close contact with an infected person, such as a household member, should quarantine in their homes and get tested for SARS-CoV-2.¶¶
These findings suggest that transmission of SARS-CoV-2 within households is high, occurs quickly, and can originate from both children and adults. Prompt adoption of disease control measures, including self-isolating at home, appropriate self-quarantine of household contacts, and all household members wearing a mask in shared spaces, can reduce the probability of household transmission.