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

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.

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A meta-analysis on the role of children in SARS-CoV-2 in household transmission clusters

Clinical Infectious Diseases ◽

10.1093/cid/ciaa1825 ◽

2020 ◽

Cited By ~ 2

Author(s):

Yanshan Zhu ◽

Conor J Bloxham ◽

Katina D Hulme ◽

Jane E Sinclair ◽

Zhen Wei Marcus Tong ◽

...

Keyword(s):

Confidence Interval ◽

Risk Ratio ◽

Attack Rate ◽

Index Case ◽

Meta Analysis ◽

Household Contacts ◽

Household Transmission ◽

Potential Vaccine ◽

Index Cases

Abstract The role of children in the spread of SARS-CoV-2 remains highly controversial. To address this issue, we performed a meta-analysis of the published literature on household SARS-CoV-2 transmission clusters (n=213 from 12 countries). Only 8 (3.8%) transmission clusters were identified as having a paediatric index case. Asymptomatic index cases were associated with a lower secondary attack in contacts than symptomatic index cases (estimate risk ratio [RR], 0.17; 95% confidence interval [CI], 0.09-0.29). To determine the susceptibility of children to household infections the secondary attack rate (SAR) in paediatric household contacts was assessed. The secondary attack rate in paediatric household contacts was lower than in adult household contacts (RR, 0.62; 95% CI, 0.42-0.91). These data have important implications for the ongoing management of the COVID-19 pandemic, including potential vaccine prioritization strategies.

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A meta-analysis on the role of children in SARS-CoV-2 in household transmission clusters

10.1101/2020.03.26.20044826 ◽

2020 ◽

Cited By ~ 25

Author(s):

Yanshan Zhu ◽

Conor J. Bloxham ◽

Katina D. Hulme ◽

Jane E. Sinclair ◽

Zhen Wei Marcus Tong ◽

...

Keyword(s):

Confidence Interval ◽

Family Member ◽

Attack Rate ◽

Index Case ◽

Meta Analysis ◽

Household Contacts ◽

Household Transmission ◽

Potential Vaccine ◽

Index Cases

ABSTRACTThe role of children in the spread of SARS-CoV-2 remains highly controversial. To address this issue, we performed a meta-analysis of the published literature on household SARS-CoV-2 transmission clusters (n=213 from 12 countries). Only 8 (3.8%) transmission clusters were identified as having a paediatric index case. Asymptomatic index cases were associated with a lower secondary attack in contacts than symptomatic index cases (estimate risk ratio [RR], 0.17; 95% confidence interval [CI], 0.09-0.29). To determine the susceptibility of children to household infections the secondary attack rate (SAR) in paediatric household contacts was assessed. The secondary attack rate in paediatric household contacts was lower than in adult household contacts (RR, 0.62; 95% CI, 0.42-0.91). These data have important implications for the ongoing management of the COVID-19 pandemic, including potential vaccine prioritization strategies.40-word summaryIn household transmission clusters of SARS-CoV-2 children are unlikely to be the index case. Children are also less likely than adults to be infected with SARS-CoV-2 from a family member.

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Role of children in household transmission of COVID-19

Archives of Disease in Childhood ◽

10.1136/archdischild-2020-319910 ◽

2020 ◽

pp. archdischild-2020-319910 ◽

Cited By ~ 13

Author(s):

Jieun Kim ◽

Young June Choe ◽

Jin Lee ◽

Young Joon Park ◽

Ok Park ◽

...

Keyword(s):

Attack Rate ◽

Index Case ◽

Clinical Findings ◽

International Travel ◽

Contact Tracing ◽

Secondary Case ◽

Household Transmission ◽

Household Members ◽

Index Cases

ObjectiveTransmissibility of COVID-19 by children in the household is not clear. Herein, we describe children’s role in household transmission of COVID-19.Design and settingAll paediatric COVID-19 index cases and their household members reported from 20 January to 6 April 2020 in South Korea were reviewed. The secondary attack rate (SAR) from child index case to household secondary case was calculated. Epidemiological and clinical findings of child index case-household secondary case pair was assessed.ResultsA total of 107 paediatric COVID-19 index cases and 248 of their household members were identified. One pair of paediatric index-secondary household case was identified, giving a household SAR of 0.5% (95% CI 0.0% to 2.6%). The index case was self-quarantined at home after international travel, stayed in her room, but shared a meal table with the secondary case.ConclusionThe SAR from children to household members was low in the setting of social distancing, underscoring the importance of rigorous contact tracing and early isolation in limiting transmission within households.

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Household secondary attack rate of COVID-19 by household size and index case characteristics

10.1101/2021.02.23.21252287 ◽

2021 ◽

Author(s):

Semra Tibebu ◽

Kevin A. Brown ◽

Nick Daneman ◽

Lauren A. Paul ◽

Sarah A. Buchan

Keyword(s):

Symptom Onset ◽

Attack Rate ◽

Index Case ◽

Household Size ◽

Residential Address ◽

Household Contacts ◽

Household Transmission ◽

Case Characteristics ◽

Index Cases

AbstractIn this population-wide study in Ontario, Canada, we investigated the household secondary attack rate (SAR) to understand its relationship to household size and index case characteristics. We identified all patients with confirmed COVID-19 between July 1 and November 30, 2020. Cases within households were matched based on reported residential address; households were grouped based on the number of household contacts. The majority of households (68.2%) had a SAR of 0%, while 3,442 (11.7%) households had a SAR ≥75%. Overall household SAR was 19.5% and was similar across household sizes, but varied across index case characteristics. Households where index cases had longer delays between symptom onset and test seeking, households with older index cases, households with symptomatic index cases, and larger households located in diverse neighborhoods, were associated with greater household SAR. Our findings present characteristics associated with greater household SARs and proposes immediate testing as a method to reduce household transmission and incidence of COVID-19.

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High variability in transmission of SARS-CoV-2 within households and implications for control

PLoS ONE ◽

10.1371/journal.pone.0259097 ◽

2021 ◽

Vol 16 (11) ◽

pp. e0259097

Author(s):

Damon J. A. Toth ◽

Alexander B. Beams ◽

Lindsay T. Keegan ◽

Yue Zhang ◽

Tom Greene ◽

...

Keyword(s):

Test Data ◽

Attack Rate ◽

Serological Test ◽

Close Contact ◽

Antibody Test ◽

High Variability ◽

Test Accuracy ◽

Household Transmission ◽

Wide Range ◽

Test Specificity

Background Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) poses a high risk of transmission in close-contact indoor settings, which may include households. Prior studies have found a wide range of household secondary attack rates and may contain biases due to simplifying assumptions about transmission variability and test accuracy. Methods We compiled serological SARS-CoV-2 antibody test data and prior SARS-CoV-2 test reporting from members of 9,224 Utah households. We paired these data with a probabilistic model of household importation and transmission. We calculated a maximum likelihood estimate of the importation probability, mean and variability of household transmission probability, and sensitivity and specificity of test data. Given our household transmission estimates, we estimated the threshold of non-household transmission required for epidemic growth in the population. Results We estimated that individuals in our study households had a 0.41% (95% CI 0.32%– 0.51%) chance of acquiring SARS-CoV-2 infection outside their household. Our household secondary attack rate estimate was 36% (27%– 48%), substantially higher than the crude estimate of 16% unadjusted for imperfect serological test specificity and other factors. We found evidence for high variability in individual transmissibility, with higher probability of no transmissions or many transmissions compared to standard models. With household transmission at our estimates, the average number of non-household transmissions per case must be kept below 0.41 (0.33–0.52) to avoid continued growth of the pandemic in Utah. Conclusions Our findings suggest that crude estimates of household secondary attack rate based on serology data without accounting for false positive tests may underestimate the true average transmissibility, even when test specificity is high. Our finding of potential high variability (overdispersion) in transmissibility of infected individuals is consistent with characterizing SARS-CoV-2 transmission being largely driven by superspreading from a minority of infected individuals. Mitigation efforts targeting large households and other locations where many people congregate indoors might curb continued spread of the virus.

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Increased household secondary attacks rates with Variant of Concern SARS-CoV-2 index cases

10.1101/2021.03.31.21254502 ◽

2021 ◽

Author(s):

Sarah A Buchan ◽

Semra Tibebu ◽

Nick Daneman ◽

Michael Whelan ◽

Thuva Vanniyasingam ◽

...

Keyword(s):

Propensity Score ◽

Attack Rate ◽

Index Case ◽

Population Based ◽

Onset Date ◽

Matched Cohort ◽

Ongoing Research ◽

Health Measures ◽

Private Households ◽

Index Cases

IMPORTANCE: Higher secondary attack rates related to variant of concern (VOC) index cases have been reported, but have not been explored within households, which continue to be an important source of coronavirus disease 2019 (COVID-19) transmission OBJECTIVE: To compare secondary attack rates in households with VOC versus non-VOC index cases. DESIGN: A retrospective cohort study of household index cases reported from February 7-27, 2021. A propensity-score matched cohort was derived to calculate adjusted estimates. SETTING: Ontario, Canada. PARTICIPANTS: A population-based cohort of all private households with index cases. We excluded cases in congregate settings, as well as households with one individual or with >1 case with the same earliest symptom onset date. EXPOSURE: VOC status, defined as either individuals confirmed as B.1.1.7 using whole genome sequencing or those that screened positive for the N501Y mutation using real-time PCR. MAIN OUTCOME AND MEASURE: Household secondary attack rate, defined as the number of household secondary cases that occurred 1-14 days after the index case divided by the total number of household secondary contacts. RESULTS: We included 1,259 index VOC and non-VOC cases in the propensity score-matched analysis. The secondary attack rate for VOC index cases in this matched cohort was 1.31 times higher than non-VOC index cases (RR=1.31, 95%CI 1.14-1.49), similar to the unadjusted estimate. In stratified analyses, the higher secondary attack rate for VOC compared to non-VOC index cases was accentuated for asymptomatic index cases (RR=1.91, 95% CI 0.96-3.80) and presymptomatic cases (RR=3.41, 95%CI 1.13-10.26) CONCLUSIONS AND RELEVANCE: This study provides strong evidence of increased transmissibility in households due to VOCs and suggests that asymptomatic and pre-symptomatic transmission may be of particular importance for VOCs. Our study suggests that more aggressive public health measures will be needed to control VOCs and that ongoing research is needed to understand mechanisms of VOC transmissibility to curb their associated morbidity and mortality.

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Epidemiology and contact tracing assessment of COVID-19 and potential risk of transmission at different exposure settings: A prospective cohort study

10.21203/rs.3.rs-442709/v1 ◽

2021 ◽

Author(s):

Abu Shadat M Noman ◽

Mohammed Rezaul Karim ◽

ASM Zahed ◽

ATM Rezaul Karim ◽

Syed S Islam

Keyword(s):

Risk Ratio ◽

Attack Rate ◽

Close Contact ◽

Household Contact ◽

Control Measures ◽

Effective Control ◽

Secondary Contact ◽

Epidemiological Characteristics ◽

Index Cases ◽

Close Contacts

Abstract Background: Transmission risk of coronavirus disease 2019 (COVID-19) to close contacts and at different exposure settings are yet to be fully understood for the evaluation of effective control measures. Methods: We traced 1171 close contact cases who were linked to 291 index cases between July 3, 2020 and September 3, 2020. Clinical and epidemiological characteristics of all index cases, close contacts, and secondary contact cases were collected and analyzed the secondary attack rate and risk of transmission at different exposure settings. Results: Median age of 291 index cases were 43.0 years (range 18.5-82.3) including 213 male and 78 females. Among all 1171 close contact cases, 39(3.3%) cases were identified as secondary infected cases. Among 39 secondary cases, 33(84.62%) cases were symptomatic and 3 (7.69%) cases were asymptomatic. Of the 33 symptomatic cases, 31(86.1%) male and 5(13.9%) female. Of these 36 symptomatic cases, 24(66.7%) cases between age 20-59 and remaining 12(33.3%) cases were age 60 and over. Of the 36 symptomatic cases, 11(30.6%) cases were identified as severe, 19(52.8%) as moderate and 6(16.7%) as mild. The overall secondary clinical attack rate was 3.07% (95% CI 2.49-3.64). The attack rate was higher among those aged between 50 to 69 years and shows higher risk of transmission than age below 50 years. The attack rate was higher among household contact (6.17%(95%CI 4.7-7.6; risk ratio 2.44[95%CI1.5-3.4]), and lower in hospital facility (2.29%,95%CI0.58-3.40; [risk ratio 0.91,95%CI 0.17-1.9]), funeral ceremony (2.53%,95%CI 0.32-4.73), work places (3.95%,95% CI2.5-5.42 [risk ratio 1.56,95%CI 0.63-2.5]), family contacts (3.87%,95%CI 2.4-5.3; risk ratio 1.53,95%CI 0.61-2.45]). Conclusions: Among all exposure settings analyzed, household contact exposure setting remained the highest transmission probability and risk of transmission of COVID-19 with the increase of age and disease severity.

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High variability in transmission of SARS-CoV-2 within households and implications for control

10.1101/2021.01.29.20248797 ◽

2021 ◽

Author(s):

Damon J.A. Toth ◽

Alexander B. Beams ◽

Lindsay T. Keegan ◽

Yue Zhang ◽

Tom Greene ◽

...

Keyword(s):

Test Data ◽

Attack Rate ◽

Serological Test ◽

Close Contact ◽

Antibody Test ◽

High Variability ◽

Test Accuracy ◽

Household Transmission ◽

Wide Range ◽

Test Specificity

AbstractBackgroundSevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) poses a high risk of transmission in close-contact indoor settings, which may include households. Prior studies have found a wide range of household secondary attack rates and may contain biases due to simplifying assumptions about transmission variability and test accuracy.MethodsWe compiled serological SARS-CoV-2 antibody test data and prior PCR test reporting from members of more than 9000 Utah households. We paired these data with a probabilistic model of household importation and transmission. We calculated a maximum likelihood estimate of the importation probability, mean and variability of household transmission probability, and sensitivity and specificity of test data. Given our household transmission estimates, we estimated the threshold of non-household transmission required for epidemic growth in the population.ResultsWe estimated that individuals in our study households had a 0.38% (95% CI 0.30% – 0.48%) chance of acquiring SARS-CoV-2 infection outside their household. Our household secondary attack rate estimate was 35% (26% – 47%), substantially higher than the crude estimate of 15% unadjusted for imperfect serological test specificity and other factors. We found evidence for high variability in individual transmissibility, with higher probability of no transmissions or many transmissions compared to standard models. With household transmission at our estimates, the average number of non-household transmissions per case must be kept below 0.40 (0.32 – 0.51) to avoid continued growth of the Utah epidemic.ConclusionsOur findings suggest that crude estimates of household secondary attack rate based on serology data without accounting for false positive tests may underestimate the true average transmissibility, even when test specificity is high. Our finding of potential high variability (overdispersion) in transmissibility of infected individuals is consistent with characterizing SARS-CoV-2 transmission being largely driven by superspreading from a minority of infected individuals. Mitigation efforts targeting large households and other locations where many people congregate indoors might curb continued spread of the virus.

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Cross-Sectional Household Transmission Study of Cryptosporidium Shows that C. Hominis Infections are A Key Risk Factor for Spread.

10.21203/rs.3.rs-659412/v1 ◽

2021 ◽

Author(s):

Caoimhe McKerr ◽

Rachel M Chalmers ◽

Kristin Elwin ◽

Heather Jones ◽

Roberto Vivancos ◽

...

Keyword(s):

Risk Factors ◽

At Risk ◽

Index Case ◽

Secondary Infection ◽

Transmission Risk ◽

Cross Sectional ◽

England And Wales ◽

Infected People ◽

North West ◽

Household Transmission

Abstract BackgroundInfection with the Cryptosporidium parasite causes over 4,000 cases of diagnosed illness (cryptosporidiosis) in England and Wales each year. The incidence of sporadic disease has not been sufficiently established, and how frequently this arises from contact with other infected people is not well documented.This project aimed to explore potential transmission in the home and attempt to identify asymptomatic infections, which might play a role in transmission. Risk factors and characteristics associated with spread of infection in the home were described including any differences between Cryptosporidium species.MethodsThe study identified cryptosporidiosis cases from North West England and Wales over a year and invited them and their household to take part. Each household was sent a study pack containing study information and a questionnaire, and stool sample kits to provide samples from consenting household members. Cryptosporidium-positive stool samples, identified by immunofluorescence microscopy, were characterised using molecular methods to help describe any patterns of transmission. Characteristics of households with and without additional cases were described, and compared using odds ratios (OR) and a multivariable logistic regression identified independent risk factors for household transmission. Data collection ran for one year, beginning in September 2018 with an initial pilot phase. ResultsWe enrolled 128 index cases and their households.Additional illness occurred in over a quarter of homes, each reporting an average of two additional cases. The majority of these were undiagnosed and unreported to surveillance. This burden was even greater in households where the index case was infected with C. hominis versus C. parvum, or the index case was under five years old, with mums and siblings most at risk of secondary infection. Only having an index case of C. hominis was independently associated with transmission in the multivariable model (OR= 4.46; p=0.01).ConclusionsCryptosporidium was a considerable burden in the home. At-risk homes were those where the index was less than five years old and/or infected with C. hominis. Of particular risk were female caregivers and siblings. Hygiene advice should be specifically directed here.This work provides evidence for humans as sources of C. hominis infection and that person-person is a key pathway. We recommend that all stools submitted for the investigation of gastrointestinal pathogens are tested for Cryptosporidium to better capture cases, inclusion of speciation data in routine surveillance, and the consideration of specific clinical advice on prevention for high-risk homes.

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High attack rates of SARS-CoV-2 infection through household-transmission: a prospective study

10.1101/2020.11.02.20224485 ◽

2020 ◽

Author(s):

Kanika Kuwelker ◽

Fan Zhou ◽

Bjørn Blomberg ◽

Sarah Lartey ◽

Karl Albert Brokstad ◽

...

Keyword(s):

Attack Rate ◽

Index Case ◽

Rt Pcr ◽

Younger Adults ◽

Household Transmission ◽

Antibody Titres ◽

Household Members ◽

Polymerase Chain ◽

A Prospective Study ◽

Rule Out

AbstractBackgroundHousehold attack rates of SARS-CoV-2 ranging from 7% to 38% have been reported, using reverse transcription polymerase chain reaction (RT-PCR) of respiratory samples. Lower attack rates were described in children, but the importance of age in household transmission dynamics remains to be clarified.MethodsDuring the first month of the outbreak, we enrolled 112 households (291 participants) in a prospective case-ascertained study, collecting demographic and clinical data from index cases and household members. Sera were collected 6-8 weeks after index case symptom onset, to measure SARS-CoV-2-specific antibodies.FindingsT Local Ethics Committee (#118664). he overall household attack rate was 45% assessed by seroconversion, and 47% when also including RT-PCR positives. Serology identified a significantly higher number of infected household members than RT-PCR. Attack rates were equally high in children (43%) and young adults (46%), but highest among household members aged ≥60 years (72%). The attack rate was 16% in asymptomatic household members, and 42% in RT-PCR negative household members. Older adults generally had higher antibody titres than younger adults. The risk of household transmission was higher when the index case had fever or dyspnoea during acute illness but not associated with cough.InterpretationSerological assays provide more accurate estimates of household secondary attack rate than RT-PCR, especially among children who have a lower RT-PCR positivity rate. Children are equally susceptible to infection as adults, but elderly show higher attack rates. Negative RT-PCR or lack of symptoms are not sufficient to rule out infection in household members.FundingHelse Vest (F-11628), Trond Mohn Foundation (TMS2020TMT05).

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