Household Secondary Attack Rate of COVID-19 and Associated Determinants

AbstractBackgroundAs of April 2, 2020, the global reported number of COVID-19 cases has crossed over 1 million with more than 55,000 deaths. The household transmissibility of SARS-CoV-2, the causative pathogen, remains elusive.MethodsBased on a comprehensive contact-tracing dataset from Guangzhou, we estimated both the population-level effective reproductive number and individual-level secondary attack rate (SAR) in the household setting. We assessed age effects on transmissibility and the infectivity of COVID-19 cases during their incubation period.ResultsA total of 195 unrelated clusters with 212 primary cases, 137 nonprimary (secondary or tertiary) cases and 1938 uninfected close contacts were traced. We estimated the household SAR to be 13.8% (95% CI: 11.1-17.0%) if household contacts are defined as all close relatives and 19.3% (95% CI: 15.5-23.9%) if household contacts only include those at the same residential address as the cases, assuming a mean incubation period of 4 days and a maximum infectious period of 13 days. The odds of infection among children (<20 years old) was only 0.26 (95% CI: 0.13-0.54) times of that among the elderly (≥60 years old). There was no gender difference in the risk of infection. COVID-19 cases were at least as infectious during their incubation period as during their illness. On average, a COVID-19 case infected 0.48 (95% CI: 0.39-0.58) close contacts. Had isolation not been implemented, this number increases to 0.62 (95% CI: 0.51-0.75). The effective reproductive number in Guangzhou dropped from above 1 to below 0.5 in about 1 week.ConclusionSARS-CoV-2 is more transmissible in households than SARS-CoV and MERS-CoV, and the elderly ≥60 years old are the most vulnerable to household transmission. Case finding and isolation alone may be inadequate to contain the pandemic and need to be used in conjunction with heightened restriction of human movement as implemented in Guangzhou.

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Vaccine effectiveness against SARS-CoV-2 transmission and infections among household and other close contacts of confirmed cases, the Netherlands, February to May 2021

Eurosurveillance ◽

10.2807/1560-7917.es.2021.26.31.2100640 ◽

2021 ◽

Vol 26 (31) ◽

Author(s):

Brechje de Gier ◽

Stijn Andeweg ◽

Rosa Joosten ◽

Ronald ter Schegget ◽

Naomi Smorenburg ◽

...

Keyword(s):

The Netherlands ◽

Confidence Interval ◽

Attack Rate ◽

Severe Disease ◽

Vaccine Effectiveness ◽

Monitoring Data ◽

High Effectiveness ◽

Household Contacts ◽

Index Cases ◽

Close Contacts

Several studies report high effectiveness of COVID-19 vaccines against SARS-CoV-2 infection and severe disease, however an important knowledge gap is the vaccine effectiveness against transmission (VET). We present estimates of the VET to household and other close contacts in the Netherlands, from February to May 2021, using contact monitoring data. The secondary attack rate among household contacts was lower for fully vaccinated than unvaccinated index cases (11% vs 31%), with an adjusted VET of 71% (95% confidence interval: 63–77).

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The first 2 months of COVID-19 contact tracing in the Northern Territory of Australia, March–April 2020

Communicable Diseases Intelligence ◽

10.33321/cdi.2020.44.53 ◽

2020 ◽

Vol 44 ◽

Author(s):

Anthony DK Draper ◽

Karen E Dempsey ◽

Rowena H Boyd ◽

Emma M Childs ◽

Hayley M Black ◽

...

Keyword(s):

Disease Control ◽

Healthcare Workers ◽

Northern Territory ◽

Contact Tracing ◽

Cruise Ship ◽

Disease Symptoms ◽

Household Contacts ◽

Close Contacts

The Northern Territory (NT) Centre for Disease Control (CDC) undertook contact tracing of all notified cases of coronavirus disease 2019 (COVID-19) within the Territory. There were 28 cases of COVID-19 notified in the NT between 1 March and 30 April 2020. In total 527 people were identified as close contacts over the same period; 493 were successfully contacted; 445 were located in the NT and were subsequently quarantined and monitored for disease symptoms daily for 14 days after contact with a confirmed COVID-19 case. Of these 445 close contacts, 4 tested positive for COVID-19 after developing symptoms; 2/46 contacts who were cruise ship passengers (4.3%, 95% CI 0.5–14.8%) and 2/51 household contacts (3.9%, 95% CI 0.5–13.5%). None of the 326 aircraft passengers or 4 healthcare workers who were being monitored in the NT as close contacts became cases.

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A comparison of COVID-19 secondary attack rate in household and close contacts compared to current risk stratification guidelines of the Kerala government

Tropical Doctor ◽

10.1177/00494755211002012 ◽

2021 ◽

pp. 004947552110020

Author(s):

Balram Rathish ◽

Arun Wilson ◽

Sonya Joy

Keyword(s):

High Risk ◽

Risk Stratification ◽

Attack Rate ◽

Low Risk ◽

Contact Tracing ◽

Index Cases ◽

Current Risk ◽

Close Contacts

COVID-19 has been found to be highly infectious with a high secondary attack rate with a R0 of 3.3. However, the secondary attack rate based on risk stratification is sparsely reported, if ever. We studied the contact tracing data for two index cases of COVID-19 with some overlap of contacts. We found that 60% of high-risk contacts and 0% of low-risk contacts of symptomatic COVID-19 patients contracted the infection, in keeping with the Kerala government contact risk stratification guidelines.

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Epidemiology and Transmission of COVID-19 in Shenzhen China: Analysis of 391 cases and 1,286 of their close contacts

10.1101/2020.03.03.20028423 ◽

2020 ◽

Cited By ~ 134

Author(s):

Qifang Bi ◽

Yongsheng Wu ◽

Shujiang Mei ◽

Chenfei Ye ◽

Xuan Zou ◽

...

Keyword(s):

General Population ◽

Disease Transmission ◽

Clinical Severity ◽

Transmission Risk ◽

Contact Tracing ◽

Initial Assessment ◽

Reproductive Number ◽

Risk Of Infection ◽

The Impact ◽

Close Contacts

AbstractBackgroundRapid spread of SARS-CoV-2 in Wuhan prompted heightened surveillance in Shenzhen and elsewhere in China. The resulting data provide a rare opportunity to measure key metrics of disease course, transmission, and the impact of control.MethodsThe Shenzhen CDC identified 391 SARS-CoV-2 cases from January 14 to February 12, 2020 and 1286 close contacts. We compare cases identified through symptomatic surveillance and contact tracing, and estimate the time from symptom onset to confirmation, isolation, and hospitalization. We estimate metrics of disease transmission and analyze factors influencing transmission risk.FindingsCases were older than the general population (mean age 45) and balanced between males (187) and females (204). Ninety-one percent had mild or moderate clinical severity at initial assessment. Three have died, 225 have recovered (median time to recovery is 21 days). Cases were isolated on average 4.6 days after developing symptoms; contact tracing reduced this by 1.9 days. Household contacts and those travelling with a case where at higher risk of infection (ORs 6 and 7) than other close contacts. The household secondary attack rate was 15%, and children were as likely to be infected as adults. The observed reproductive number was 0.4, with a mean serial interval of 6.3 days.InterpretationOur data on cases as well as their infected and uninfected close contacts provide key insights into SARS-CoV-2 epidemiology. This work shows that heightened surveillance and isolation, particularly contact tracing, reduces the time cases are infectious in the community, thereby reducing R. Its overall impact, however, is uncertain and highly dependent on the number of asymptomatic cases. We further show that children are at similar risk of infection as the general population, though less likely to have severe symptoms; hence should be considered in analyses of transmission and control.

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Adherence and Association of Digital Proximity Tracing App Notifications With Earlier Time to Quarantine: Results From the Zurich SARS-CoV-2 Cohort Study

International Journal of Public Health ◽

10.3389/ijph.2021.1603992 ◽

2021 ◽

Vol 66 ◽

Author(s):

Tala Ballouz ◽

Dominik Menges ◽

Hélène E. Aschmann ◽

Anja Domenghino ◽

Jan S. Fehr ◽

...

Keyword(s):

Cohort Study ◽

Population Based ◽

Contact Tracing ◽

Time To Event ◽

Household Contacts ◽

Close Contacts

Objectives: We aimed to evaluate the effectiveness of the SwissCovid digital proximity tracing (DPT) app in notifying exposed individuals and prompting them to quarantine earlier compared to individuals notified only by manual contact tracing (MCT).Methods: A population-based sample of cases and close contacts from the Zurich SARS-CoV-2 Cohort was surveyed regarding SwissCovid app use and SARS-CoV-2 exposure. We descriptively analyzed app adherence and effectiveness, and evaluated its effects on the time between exposure and quarantine among contacts using stratified multivariable time-to-event analyses.Results: We included 393 SARS-CoV-2 infected cases and 261 close contacts. 62% of cases reported using SwissCovid and among those, 88% received and uploaded a notification code. 71% of close contacts were app users, of which 38% received a warning. Non-household contacts notified by SwissCovid started quarantine 1 day earlier and were more likely to quarantine earlier than those not warned by the app (HR 1.53, 95% CI 1.15–2.03).Conclusion: These findings provide evidence that DPT may reach exposed contacts faster than MCT, with earlier quarantine and potential interruption of SARS-CoV-2 transmission chains.

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Characterizing super-spreaders using population-level weighted social networks in rural communities

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2021.0123 ◽

2021 ◽

Vol 380 (2214) ◽

Author(s):

Shivkumar Vishnempet Shridhar ◽

Marcus Alexander ◽

Nicholas A. Christakis

Keyword(s):

Rural Communities ◽

Disease Transmission ◽

Data Science ◽

Population Level ◽

Respiratory Illness ◽

Individual Characteristics ◽

Contact Tracing ◽

Transmission Model ◽

Infectious Period ◽

Interaction Patterns

Sociocentric network maps of entire populations, when combined with data on the nature of constituent dyadic relationships, offer the dual promise of advancing understanding of the relevance of networks for disease transmission and of improving epidemic forecasts. Here, using detailed sociocentric data collected over 4 years in a population of 24 702 people in 176 villages in Honduras, along with diarrhoeal and respiratory disease prevalence, we create a social-network-powered transmission model and identify super-spreading nodes as well as the nodes most vulnerable to infection, using agent-based Monte Carlo network simulations. We predict the extent of outbreaks for communicable diseases based on detailed social interaction patterns. Evidence from three waves of population-level surveys of diarrhoeal and respiratory illness indicates a meaningful positive correlation with the computed super-spreading capability and relative vulnerability of individual nodes. Previous research has identified super-spreaders through retrospective contact tracing or simulated networks. By contrast, our simulations predict that a node’s super-spreading capability and its vulnerability in real communities are significantly affected by their connections, the nature of the interaction across these connections, individual characteristics (e.g. age and sex) that affect a person’s ability to disperse a pathogen, and also the intrinsic characteristics of the pathogen (e.g. infectious period and latency). This article is part of the theme issue ‘Data science approach to infectious disease surveillance’.

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Tracking the COVID-19 pandemic in Australia using genomics

10.1101/2020.05.12.20099929 ◽

2020 ◽

Cited By ~ 21

Author(s):

Torsten Seemann ◽

Courtney Lane ◽

Norelle Sherry ◽

Sebastian Duchene ◽

Anders Goncalves da Silva ◽

...

Keyword(s):

Public Health ◽

Genome Sequencing ◽

Population Level ◽

Genomic Diversity ◽

Contact Tracing ◽

Internal Quality ◽

Reproductive Number ◽

Healthcare Facilities ◽

Travel Restrictions ◽

Response Team

BACKGROUND: Whole-genome sequencing of pathogens can improve resolution of outbreak clusters and define possible transmission networks. We applied high-throughput genome sequencing of SARS-CoV-2 to 75% of cases in the State of Victoria (population 6.24 million) in Australia. METHODS: Cases of SARS-CoV-2 infection were detected through active case finding and contact tracing. A dedicated SARS-CoV-2 multidisciplinary genomic response team was formed to enable rapid integration of epidemiological and genomic data. Phylodynamic analysis was performed to assess the putative impact of social restrictions. RESULTS: Between 25 January and 14 April 2020, 1,333 COVID-19 cases were reported in Victoria, with a peak in late March. After applying internal quality control parameters, 903 samples were included in genomic analyses. Sequenced samples from Australia were representative of the global diversity of SARS-CoV-2, consistent with epidemiological findings of multiple importations and limited onward transmission. In total, 76 distinct genomic clusters were identified; these included large clusters associated with social venues, healthcare facilities and cruise ships. Sequencing of sequential samples from 98 patients revealed minimal intra-patient SARS-CoV-2 genomic diversity. Phylodynamic modelling indicated a significant reduction in the effective viral reproductive number (Re) from 1.63 to 0.48 after the implementation of travel restrictions and population-level physical distancing. CONCLUSIONS: Our data provide a comprehensive framework for the use of SARS-CoV-2 genomics in public health responses. The application of genomics to rapidly identify SARS-CoV-2 transmission chains will become critically important as social restrictions ease globally. Public health responses to emergent cases must be swift, highly focused and effective.

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High transmissibility of COVID-19 near symptom onset

10.1101/2020.03.18.20034561 ◽

2020 ◽

Cited By ~ 19

Author(s):

Hao-Yuan Cheng ◽

Shu-Wan Jian ◽

Ding-Ping Liu ◽

Ta-Chou Ng ◽

Wan-Ting Huang ◽

...

Keyword(s):

Symptom Onset ◽

Attack Rate ◽

Paired Data ◽

Rapid Reduction ◽

Social Distancing ◽

Household Contacts ◽

Exposure Windows ◽

Index Cases ◽

Over Time ◽

Close Contacts

AbstractBackgroundThe dynamics of coronavirus disease 2019 (COVID-19) transmissibility after symptom onset remains unknown.MethodsWe conducted a prospective case-ascertained study on laboratory-confirmed COVID-19 cases and their contacts. Secondary clinical attack rate (considering symptomatic cases only) was analyzed for different exposure windows after symptom onset of index cases and for different exposure settings.ResultsThirty-two confirmed patients were enrolled and 12 paired data (index-secondary cases) were identified among the 1,043 contacts. The secondary clinical attack rate was 0.9% (95% CI 0.5–1.7%). The attack rate was higher among those whose exposure to index cases started within five days of symptom onset (2.4%, 95% CI 1.1–4.5%) than those who were exposed later (zero case from 605 close contacts, 95% CI 0–0.61%). The attack rate was also higher among household contacts (13.6%, 95% CI 4.7–29.5%) and non- household family contacts (8.5%, 95% CI 2.4–20.3%) than that in healthcare or other settings. The higher secondary clinical attack rate for contacts near symptom onset remained when the analysis was restricted to household and family contacts. There was a trend of increasing attack rate with the age of contacts (p for trend < 0.001).ConclusionsHigh transmissibility of COVID-19 near symptom onset suggests that finding and isolating symptomatic patients alone may not suffice to contain the epidemic, and more generalized social distancing measures are required. Rapid reduction of transmissibility over time implies that prolonged hospitalization of mild cases might not be necessary in large epidemics.

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Digital proximity tracing app notifications lead to faster quarantine in non-household contacts: results from the Zurich SARS-CoV-2 Cohort Study

10.1101/2020.12.21.20248619 ◽

2020 ◽

Author(s):

Tala Ballouz ◽

Dominik Menges ◽

Helene E Aschmann ◽

Anja Domenghino ◽

Jan S Fehr ◽

...

Keyword(s):

Cohort Study ◽

Population Based ◽

Contact Tracing ◽

Household Contacts ◽

Health Directorate ◽

Multivariable Analyses ◽

University Of Zurich ◽

Exposure Setting ◽

Index Cases ◽

Close Contacts

AbstractBackgroundDigital proximity tracing (DPT) apps may warn exposed individuals faster than manual contact tracing (MCT), leading to earlier interruption of transmission chains through quarantine. However, it is yet unclear whether these apps lead to a reduction in transmissions under real-world conditions. This study aimed at evaluating whether the SwissCovid DPT app is effective in warning close contacts of SARS-CoV-2 infected cases and prompting them to quarantine earlier.MethodsA population-based sample of adult index cases and close contacts identified through MCT and enrolled in the Zurich SARS-CoV-2 Cohort study were surveyed regarding use of the SwissCovid app and SARS-CoV-2 exposure setting. We analyzed ooutcomes related to app effectiveness and adherence (i.e., receipt and uploading of notification codes by index cases; receipt of app warnings and steps taken by close contacts). Furthermore, we performed adjusted time-to-event analyses stratified by exposure setting to estimate the effect of the app on time between relevant exposure and entering quarantine among close contacts.FindingsWe included 393 index cases and 261 close contacts in the analysis. Among index cases using SwissCovid, 88% reported receiving and uploading a notification code in the app to trigger a warning among proximity contacts. Among close contacts using the app, 38% reported receiving an app warning due to the risk exposure. We found that non-household contacts who were notified by the app started quarantine at a median of 2 days after exposure, while those not notified started quarantine at a median of 3 days. In stratified multivariable analyses, app notified contacts had a greater probability of going into quarantine earlier than those without app notification (HR 1·53, 95% CI 1·15-2·03).InterpretationOur study showed that non-household contacts notified by the app started quarantine one day earlier than those not notified by the app. These findings constitute the first evidence that DPT may reach exposed contacts faster than MCT, leading to earlier quarantine and potential interruption of SARS-CoV-2 transmission chains.FundingCantonal Health Directorate Zurich, University of Zurich Foundation and the Swiss Federal Office of Public Health.

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Secondary attack rate of COVID-19 in household contacts: a systematic review

QJM ◽

10.1093/qjmed/hcaa232 ◽

2020 ◽

Vol 113 (12) ◽

pp. 841-850 ◽

Cited By ~ 8

Author(s):

K Shah ◽

D Saxena ◽

D Mavalankar

Keyword(s):

Systematic Review ◽

Attack Rate ◽

Evidence Synthesis ◽

Geographic Location ◽

Critical Factor ◽

Transmission Probability ◽

Contact Tracing ◽

Secondary Transmission ◽

Household Contacts ◽

Household Transmission

Summary Coronavirus disease 2019 (COVID-19) is a novel virus with continuously evolving transmission trends. Contact tracing and quarantining of positive cases are chief strategies of disease control that has been accepted globally, though scientific knowledge regarding household transmission of the COVID-19 through contact of positive case is sparse. Current systematic review was planned to assess global statistics and characteristics of household secondary attack rate (SAR) of COVID-19. Eligible articles were retrieved through search of—MEDLINE, SCOPUS and EMBASE for the period December 2019 to 15 June 2020. Search terms were developed to identify articles reporting household SARs in various countries. After initial screening of 326 articles, 13 eligible studies were included in the final evidence synthesis. We found that SAR varies widely across countries with lowest reported rate as 4.6% and highest as 49.56%. The rates were unaffected by confounders such as population of the country, lockdown status and geographic location. Review suggested greater vulnerability of spouse and elderly population for secondary transmission than other household members. It was also observed that quarantining and isolation are most effective strategies for prevention of the secondary transmission of the disease. Symptomatic status of the index case emerged to be a critical factor, with very low transmission probability during asymptomatic phase. Present review findings recommend that adequate measures should be provided to protect the vulnerable population as only case tracing and quarantining might be insufficient. It should be combined with advisory for limiting household contacts and active surveillance for symptom onset.

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