Household transmission of SARS-CoV-2: a systematic review and meta-analysis of secondary attack rate

Abstract

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is spread by direct, indirect, or close contact with infected people via infected respiratory droplets or saliva. Crowded indoor environments with sustained close contact and conversations are a particularly high-risk setting.

Methods: We performed a meta-analysis through July 29, 2020 of SARS-CoV-2 household secondary attack rate (SAR), disaggregating by several covariates (contact type, symptom status, adult/child contacts, contact sex, relationship to index case, index case sex, number of contacts in household, coronavirus).

Findings: We identified 40 relevant published studies that report household secondary transmission. The estimated overall household SAR was 18.8% (95% confidence interval [CI]: 15.4%-22.2%), which is higher than previously observed SARs for SARS-CoV and MERS-CoV. We observed that household SARs were significantly higher from symptomatic index cases than asymptomatic index cases, to adult contacts than children contacts, to spouses than other family contacts, and in households with one contact than households with three or more contacts.

Interpretation: To prevent the spread of SARS-CoV-2, people are being asked to stay at home worldwide. With suspected or confirmed infections referred to isolate at home, household transmission will continue to be a significant source of transmission.

Figure 1.

Flowchart for review of household secondary attack rate

Figure 2.

Secondary attack rates (SAR) for household contacts and family contacts (including individuals outside the index case household).

Figure 3.

Secondary attack rates (SAR) from symptomatic and asymptomatic index cases to household and family (*) contacts.

Figure 4.

The average number of contacts per household, secondary attack rate (SAR), and proportion of households reporting any secondary transmission from index cases. The blue triangles represent the expected proportion of households with any secondary transmission (see Appendix for further details).

Figure 5.

Secondary attack rates (SAR) for adult (≥18 years) and children (<18 years) household and family (*) contacts.

Figure 6.

Secondary attack rates (SAR) for household and family (*) contacts by contact sex.

Figure 7.

Secondary attack rates (SAR) for household and family (*) contacts by relationship to index case (spouse, other).

Figure 8.

Secondary attack rates (SAR) for household contacts by index case sex.

Figure 9.

Secondary attack rates (SAR) by the number of contacts in the household.

Figure 10.

Household secondary attack rates (SAR) for severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East Respiratory Syndrome coronavirus (MERS-CoV).