A meta-analysis of 54 studies found that the estimated secondary attack rate for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in households was 16.6%, higher than the observed rates for both SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV). The study was published in JAMA Network Open.
Investigators searched for published studies on PubMed through October 19, 2020. A total of 54 studies including 77,758 participants were identified. Of these, 16 studies (29.6%) were at a high risk for bias, 27 studies (50.0%) were at a moderate risk, and 11 studies (20.4%) were at a low risk.
The estimated mean secondary attack rate for SARS-CoV-2 in household contacts was 16.4% (95% CI, 13.4%-19.6%) and was 17.4% (95% CI, 12.7%-22.5%) for family contacts. This was higher than secondary attack rates for SARS-CoV (7.5%; 95% CI, 4.8%-10.7%) and MERS-CoV (4.7%; 95% CI, 0.9%-10.7%). The secondary attack rates did not change significantly when eliminating studies with high risk for bias. There were also no significant differences in secondary attack rates between 21 studies in China and 33 studies from other countries.
For symptomatic index cases the estimated mean household secondary attack rate was 18.0% (95% CI, 14.2%-22.1%). This was significantly higher than the estimated mean household secondary attack rate for asymptomatic or presymptomatic index cases (0.7%; 95% CI, 0%-4.9%; P <.001). Investigators also found evidence of infection clusters within households.
Based on data from 15 studies, the estimated mean household secondary attack rate was significantly higher for adults (28.3%; 95% CI, 20.2%-37.1%) than for children (16.8%; 95% CI, 12.3%-21.7%; P <.001). Studies also indicated that the attack rate was significantly higher to spouses (37.8%; 95% CI, 25.8%-50.5%) than to other contacts (17.8%; 95% CI, 11.7%-24.8%). The mean household secondary attack rate was significantly higher for households with 1 contact (41.5%; 95% CI, 31.7%-51.7%) compared with households with at least 3 contacts (22.8%; 95% CI, 13.6%-33.5%; P <.001), but no difference was seen in households with 2 contacts (38.6%; 95% CI, 17.9%-61.6%).
Important limitations to the analysis were the large amount of heterogeneity across studies, including variations in testing and monitoring strategies and the rates of community transmission. Most studies also did not describe whether secondary infections could have been acquired outside the home.
“[H]ouseholds are and will continue to be important venues for transmission, even where community transmission is reduced,” the investigators concluded.
Madewell ZJ, Yang Y, Longini Jr IM, Halloran ME, Dean NE. Household transmission of SARS-CoV-2: A systematic review and meta-analysis. JAMA Netw Open. 2020;3(12):e2031756. doi:10.1001/jamanetworkopen.2020.31756.