Household Transmission of SARS-CoV-2: A Systematic Review and Meta-analysis | Global Health | JAMA Network Open | JAMA Network
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    7 Comments for this article
    Larry Martinez, N/A | N/A
    "Household secondary attack rates were increased from symptomatic index cases (18.0%; 95% CI, 14.2%-22.1%) than from asymptomatic index cases (0.7%; 95% CI, 0%-4.9%)..."

    Does that mean that if someone in my household is symptomatic, I have an 18% chance to contract the virus? And a .7% chance to contract it from an asymptomatic household member?
    Response to Larry Martinez
    Alfred Stolfa, BE, Cert IV Public Safety | None

    Regarding your question:

    "Does that mean that if someone in my household is symptomatic, I have an 18% chance to contract the virus? And a .7% chance to contract it from an asymptomatic household member?"

    The percentages quoted are based on analysis of metadata, not the specific risk profile anyone of us may experience in their own home should a member of our family be living there while infectious with SARS-CoV-2 (COVID-19). The nuances and wide variability in human behaviours cannot be possibly accounted for in such a retrospective metadata study because the study's authors do
    not have access to all the individuals to confirm the exact circumstances of their contact with infected parties.

    If the infectious individual remained quarantine in a single room and instances of direct or close proximity contact were ruled out, meals/ablutions were taken in isolation from other family members, all surfaces in common areas (bathroom, kitchen, etc.) were regularly wiped down after the infected person accessed them, and all individuals work masks, YOUR risk of contracting the infection would be significantly less than if none of these measures were in place and the infected individual roamed the house and interacted with family members in a 'business as usual' manner.

    Hope this helps.
    statistical error?
    Jeffrey Archinal, MD | Akron Children's Hospital, Akron, OH
    I'll admit I'm a primary care doc and not a researcher, but I would like help understanding how one could conclude from the 4 studies of asymptomatic people that there's a 0.7% secondary attack rate? One study had 6 positives out of 111 contacts (5.4%), another has 1 out of 23 (4.3%), another had 0 out of 15, and finally 0 out of 2.

    I know there's more statistics going on then crudely adding up the numbers, but for a simple PCP crudely adding up the numbers, that looks like we have 7 positives out of 151 contacts, or
    4.6%. How does one get from here to the reported 0.7%? If it's some weird statistical thing involving the tiny studies of 2 and 15 contacts, especially if we're talking about an event that only happens 0.7-4.6% of the time, I'm curious if they are worth including in the analysis?

    The decision to include those studies resulted in a somewhat-popular political commentator using this finding to say masks don't work, since the secondary attack rate in this study wasn't found to be statistically different from 0. This study is making people feel justified to not wear a mask, and I don't see any way this finding could have been reached except by a mistake, either as a result of a flat-out miscalculation, or a faulty decision to include two tiny studies that skewed the numbers.
    Secondary attack rates in the asymptomatic subgroup
    Stephen Friedman, MD, MPH |
    In supplemental figure 8, the authors presented four studies with secondary attack rates of 6/111, 1/23, 0/2 and 0/15.
    Based on the random effects model multivariable analysis, they estimated the transmission rate as 0.7%. Can the authors explain how the significant variables in the model affected the calculation of the transmission rate to produce an estimate different from the rates in the four studies? Can the authors also comment on whether these four studies (three with sample size less than 25) provide a reliable estimate of the secondary attack rate from asymptomatic individuals?
    Stephen Friedman, MD, MPH
    Comment from the authors
    Zachary Madewell, PhD, MPH | University of Florida
    Thank you for your interest in our paper. In this sub-analysis of the household studies from our main analysis, we separated papers reporting index cases identified as symptomatic versus asymptomatic/pre-symptomatic. We noted lower transmission from this latter group, though we state that there was much less data. For this reason, we view the qualitative result as noteworthy but requiring further exploration. Since we relied upon other studies in the literature, we were unable to separate out fully asymptomatic index cases (who never develop symptoms) from pre-symptomatic index cases. A more recent meta-analysis has focused directly on separating these two groups ( The growing literature indicates that, while individuals can be similarly infectious during the pre-symptomatic and symptomatic phases, individuals who are fully asymptomatic are less infectious to others (summary secondary attack rate of 1% from Qiu et al. 2021). This may explain the low secondary attack rate we observed in our sub-analysis.

    Regarding the methods used to calculate our point estimate, we used a restricted maximum-likelihood estimator model to yield Freeman-Tukey double arcsine–transformed point estimates and 95% CI for secondary attack rate for each subgroup analyzed, with a random effect for each study. This method is often used in meta-analyses and was recently used in another study describing asymptomatic transmission of SARS-CoV-2 ( When estimates are near zero, the Freeman-Tukey double arcsine–transformation can weight the point estimate more heavily towards zero than other methods. Other methods would return a point estimate closer to the raw combined proportion, but the qualitative conclusion of lower transmission would be the same.
    Asymptomatic Spread
    Paul D'Hondt |
    Thank for you clarifying your asymptomatic values. This value of 0.7% is being used by the anti-vax folks to indicate Covid isn't serious. Certainly you could have forseen this?
    Confusion About Asymptomatic / Presymptomatic Attack Rates
    Danielle Fong |
    I'm confused about the cited asymptomatic and presymptomatic attack rates. Both the results and the more detailed discussion cite 0.7% as the attack rate (in the centre of the CI "(0.7%; 95% CI, 0%-4.9%; P < .001)"

    I went through each of the 4 studies referenced [26,43,44,52] and I'm confused as to how the meta analysis arrives at a 0.7% asymptomatic / presymptomatic attack rate. The highest n in any of the studies is the study in Brunei, with 111 cases. There the secondary attack rate (SAR) for asymptomatic people is 4.4% and for presymptomatic people it is 6.1%. The second
    highest n is 23, which has a SAR of 4% for the (single!) presymptomatic case.

    The other two studies identified no cases of asymptomatic or presymptomatic transmission, but these studies have only 2 and 15 cases respectively: the US [44] study warns that they weren't testing for asymptomatic carriers at all, and the Seoul [52] study warns that "given the high degree of self-quarantine and isolation measures that were instituted after March 8 among this cohort, our analyses might have not detected the actual transmissibility in asymptomatic COVID-19 case-patients. Robust mass testing of all suspected case-patients might have prevented asymptomatic transmission because asymptomatic persons were given information about their possible infection and therefore might have self-isolated from their household members."

    I cannot come up with any weighting of the studies that makes any sense to me whether the SAR works out to anything close to 0.7%. Weight by n gives 4.6%. Weight by study (why would you do this) gives 2.4%. How can you get 0.7% without way overweighting the studies with small n, not to mention the concerns above?
    Original Investigation
    Global Health
    December 14, 2020

    Household Transmission of SARS-CoV-2: A Systematic Review and Meta-analysis

    Author Affiliations
    • 1Department of Biostatistics, University of Florida, Gainesville
    • 2Fred Hutchinson Cancer Research Center, Seattle, Washington
    • 3Department of Biostatistics, University of Washington, Seattle
    JAMA Netw Open. 2020;3(12):e2031756. doi:10.1001/jamanetworkopen.2020.31756
    Key Points

    Question  What is the household secondary attack rate for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)?

    Findings  In this meta-analysis of 54 studies with 77 758 participants, the estimated overall household secondary attack rate was 16.6%, higher than observed secondary attack rates for SARS-CoV and Middle East respiratory syndrome coronavirus. Controlling for differences across studies, secondary attack rates were higher in households from symptomatic index cases than asymptomatic index cases, to adult contacts than to child contacts, to spouses than to other family contacts, and in households with 1 contact than households with 3 or more contacts.

    Meaning  These findings suggest that households are and will continue to be important venues for transmission, even in areas where community transmission is reduced.


    Importance  Crowded indoor environments, such as households, are high-risk settings for the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

    Objectives  To examine evidence for household transmission of SARS-CoV-2, disaggregated by several covariates, and to compare it with other coronaviruses.

    Data Source  PubMed, searched through October 19, 2020. Search terms included SARS-CoV-2 or COVID-19 with secondary attack rate, household, close contacts, contact transmission, contact attack rate, or family transmission.

    Study Selection  All articles with original data for estimating household secondary attack rate were included. Case reports focusing on individual households and studies of close contacts that did not report secondary attack rates for household members were excluded.

    Data Extraction and Synthesis  Meta-analyses were done using a restricted maximum-likelihood estimator model to yield a point estimate and 95% CI for secondary attack rate for each subgroup analyzed, with a random effect for each study. To make comparisons across exposure types, study was treated as a random effect, and exposure type was a fixed moderator. The Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline was followed.

    Main Outcomes and Measures  Secondary attack rate for SARS-CoV-2, disaggregated by covariates (ie, household or family contact, index case symptom status, adult or child contacts, contact sex, relationship to index case, adult or child index cases, index case sex, number of contacts in household) and for other coronaviruses.

    Results  A total of 54 relevant studies with 77 758 participants reporting household secondary transmission were identified. Estimated household secondary attack rate was 16.6% (95% CI, 14.0%-19.3%), 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%). Household secondary attack rates were increased from symptomatic index cases (18.0%; 95% CI, 14.2%-22.1%) than from asymptomatic index cases (0.7%; 95% CI, 0%-4.9%), to adult contacts (28.3%; 95% CI, 20.2%-37.1%) than to child contacts (16.8%; 95% CI, 12.3%-21.7%), to spouses (37.8%; 95% CI, 25.8%-50.5%) than to other family contacts (17.8%; 95% CI, 11.7%-24.8%), and in households with 1 contact (41.5%; 95% CI, 31.7%-51.7%) than in households with 3 or more contacts (22.8%; 95% CI, 13.6%-33.5%).

    Conclusions and Relevance  The findings of this study suggest that given that individuals with suspected or confirmed infections are being referred to isolate at home, households will continue to be a significant venue for transmission of SARS-CoV-2.