tetano
Editor, Senior Moderator
Lancet Infect Dis
. 2020 Nov 2;S1473-3099(20)30833-1.
doi: 10.1016/S1473-3099(20)30833-1. Online ahead of print.
SARS-CoV-2 seroprevalence and transmission risk factors among high-risk close contacts: a retrospective cohort study
Oon Tek Ng[SUP] 1 [/SUP], Kalisvar Marimuthu[SUP] 2 [/SUP], Vanessa Koh[SUP] 3 [/SUP], Junxiong Pang[SUP] 4 [/SUP], Kyaw Zaw Linn[SUP] 3 [/SUP], Jie Sun[SUP] 4 [/SUP], Liang De Wang[SUP] 3 [/SUP], Wan Ni Chia[SUP] 5 [/SUP], Charles Tiu[SUP] 5 [/SUP], Monica Chan[SUP] 3 [/SUP], Li Min Ling[SUP] 3 [/SUP], Shawn Vasoo[SUP] 3 [/SUP], Mohammad Yazid Abdad[SUP] 3 [/SUP], Po Ying Chia[SUP] 6 [/SUP], Tau Hong Lee[SUP] 3 [/SUP], Ray Junhao Lin[SUP] 3 [/SUP], Sapna P Sadarangani[SUP] 6 [/SUP], Mark I-Cheng Chen[SUP] 4 [/SUP], Zubaidah Said[SUP] 7 [/SUP], Lalitha Kurupatham[SUP] 7 [/SUP], Rachael Pung[SUP] 7 [/SUP], Lin-Fa Wang[SUP] 5 [/SUP], Alex R Cook[SUP] 4 [/SUP], Yee-Sin Leo[SUP] 8 [/SUP], Vernon Jm Lee[SUP] 9 [/SUP]
Affiliations
Abstract
Background: The proportion of asymptomatic carriers and transmission risk factors of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among household and non-household contacts remains unclear. In Singapore, extensive contact tracing by the Ministry of Health for every diagnosed COVID-19 case, and legally enforced quarantine and intensive health surveillance of close contacts provided a rare opportunity to determine asymptomatic attack rates and SARS-CoV-2 transmission risk factors among community close contacts of patients with COVID-19.
Methods: This retrospective cohort study involved all close contacts of confirmed COVID-19 cases in Singapore, identified between Jan 23 and April 3, 2020. Household contacts were defined as individuals who shared a residence with the index COVID-19 case. Non-household close contacts were defined as those who had contact for at least 30 min within 2 m of the index case. All patients with COVID-19 in Singapore received inpatient treatment, with access restricted to health-care staff. All close contacts were quarantined for 14 days with thrice-daily symptom monitoring via telephone. Symptomatic contacts underwent PCR testing for SARS-CoV-2. Secondary clinical attack rates were derived from the prevalence of PCR-confirmed SARS-CoV-2 among close contacts. Consenting contacts underwent serology testing and detailed exposure risk assessment. Bayesian modelling was used to estimate the prevalence of missed diagnoses and asymptomatic SARS-CoV-2-positive cases. Univariable and multivariable logistic regression models were used to determine SARS-CoV-2 transmission risk factors.
Findings: Between Jan 23 and April 3, 2020, 7770 close contacts (1863 household contacts, 2319 work contacts, and 3588 social contacts) linked to 1114 PCR-confirmed index cases were identified. Symptom-based PCR testing detected 188 COVID-19 cases, and 7582 close contacts completed quarantine without a positive SARS-CoV-2 PCR test. Among 7518 (96?8%) of the 7770 close contacts with complete data, the secondary clinical attack rate was 5?9% (95% CI 4?9-7?1) for 1779 household contacts, 1?3% (0?9-1?9) for 2231 work contacts, and 1?3% (1?0-1?7) for 3508 social contacts. Bayesian analysis of serology and symptom data obtained from 1150 close contacts (524 household contacts, 207 work contacts, and 419 social contacts) estimated that a symptom-based PCR-testing strategy missed 62% (95% credible interval 55-69) of COVID-19 diagnoses, and 36% (27-45) of individuals with SARS-CoV-2 infection were asymptomatic. Sharing a bedroom (multivariable odds ratio [OR] 5?38 [95% CI 1?82-15?84]; p=0?0023) and being spoken to by an index case for 30 min or longer (7?86 [3?86-16?02]; p<0?0001) were associated with SARS-CoV-2 transmission among household contacts. Among non-household contacts, exposure to more than one case (multivariable OR 3?92 [95% CI 2?07-7?40], p<0?0001), being spoken to by an index case for 30 min or longer (2?67 [1?21-5?88]; p=0?015), and sharing a vehicle with an index case (3?07 [1?55-6?08]; p=0?0013) were associated with SARS-CoV-2 transmission. Among both household and non-household contacts, indirect contact, meal sharing, and lavatory co-usage were not independently associated with SARS-CoV-2 transmission.
Interpretation: Targeted community measures should include physical distancing and minimising verbal interactions. Testing of all household contacts, including asymptomatic individuals, is warranted.
Funding: Ministry of Health of Singapore, National Research Foundation of Singapore, and National Natural Science Foundation of China.
. 2020 Nov 2;S1473-3099(20)30833-1.
doi: 10.1016/S1473-3099(20)30833-1. Online ahead of print.
SARS-CoV-2 seroprevalence and transmission risk factors among high-risk close contacts: a retrospective cohort study
Oon Tek Ng[SUP] 1 [/SUP], Kalisvar Marimuthu[SUP] 2 [/SUP], Vanessa Koh[SUP] 3 [/SUP], Junxiong Pang[SUP] 4 [/SUP], Kyaw Zaw Linn[SUP] 3 [/SUP], Jie Sun[SUP] 4 [/SUP], Liang De Wang[SUP] 3 [/SUP], Wan Ni Chia[SUP] 5 [/SUP], Charles Tiu[SUP] 5 [/SUP], Monica Chan[SUP] 3 [/SUP], Li Min Ling[SUP] 3 [/SUP], Shawn Vasoo[SUP] 3 [/SUP], Mohammad Yazid Abdad[SUP] 3 [/SUP], Po Ying Chia[SUP] 6 [/SUP], Tau Hong Lee[SUP] 3 [/SUP], Ray Junhao Lin[SUP] 3 [/SUP], Sapna P Sadarangani[SUP] 6 [/SUP], Mark I-Cheng Chen[SUP] 4 [/SUP], Zubaidah Said[SUP] 7 [/SUP], Lalitha Kurupatham[SUP] 7 [/SUP], Rachael Pung[SUP] 7 [/SUP], Lin-Fa Wang[SUP] 5 [/SUP], Alex R Cook[SUP] 4 [/SUP], Yee-Sin Leo[SUP] 8 [/SUP], Vernon Jm Lee[SUP] 9 [/SUP]
Affiliations
- PMID: 33152271
- DOI: 10.1016/S1473-3099(20)30833-1
Abstract
Background: The proportion of asymptomatic carriers and transmission risk factors of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among household and non-household contacts remains unclear. In Singapore, extensive contact tracing by the Ministry of Health for every diagnosed COVID-19 case, and legally enforced quarantine and intensive health surveillance of close contacts provided a rare opportunity to determine asymptomatic attack rates and SARS-CoV-2 transmission risk factors among community close contacts of patients with COVID-19.
Methods: This retrospective cohort study involved all close contacts of confirmed COVID-19 cases in Singapore, identified between Jan 23 and April 3, 2020. Household contacts were defined as individuals who shared a residence with the index COVID-19 case. Non-household close contacts were defined as those who had contact for at least 30 min within 2 m of the index case. All patients with COVID-19 in Singapore received inpatient treatment, with access restricted to health-care staff. All close contacts were quarantined for 14 days with thrice-daily symptom monitoring via telephone. Symptomatic contacts underwent PCR testing for SARS-CoV-2. Secondary clinical attack rates were derived from the prevalence of PCR-confirmed SARS-CoV-2 among close contacts. Consenting contacts underwent serology testing and detailed exposure risk assessment. Bayesian modelling was used to estimate the prevalence of missed diagnoses and asymptomatic SARS-CoV-2-positive cases. Univariable and multivariable logistic regression models were used to determine SARS-CoV-2 transmission risk factors.
Findings: Between Jan 23 and April 3, 2020, 7770 close contacts (1863 household contacts, 2319 work contacts, and 3588 social contacts) linked to 1114 PCR-confirmed index cases were identified. Symptom-based PCR testing detected 188 COVID-19 cases, and 7582 close contacts completed quarantine without a positive SARS-CoV-2 PCR test. Among 7518 (96?8%) of the 7770 close contacts with complete data, the secondary clinical attack rate was 5?9% (95% CI 4?9-7?1) for 1779 household contacts, 1?3% (0?9-1?9) for 2231 work contacts, and 1?3% (1?0-1?7) for 3508 social contacts. Bayesian analysis of serology and symptom data obtained from 1150 close contacts (524 household contacts, 207 work contacts, and 419 social contacts) estimated that a symptom-based PCR-testing strategy missed 62% (95% credible interval 55-69) of COVID-19 diagnoses, and 36% (27-45) of individuals with SARS-CoV-2 infection were asymptomatic. Sharing a bedroom (multivariable odds ratio [OR] 5?38 [95% CI 1?82-15?84]; p=0?0023) and being spoken to by an index case for 30 min or longer (7?86 [3?86-16?02]; p<0?0001) were associated with SARS-CoV-2 transmission among household contacts. Among non-household contacts, exposure to more than one case (multivariable OR 3?92 [95% CI 2?07-7?40], p<0?0001), being spoken to by an index case for 30 min or longer (2?67 [1?21-5?88]; p=0?015), and sharing a vehicle with an index case (3?07 [1?55-6?08]; p=0?0013) were associated with SARS-CoV-2 transmission. Among both household and non-household contacts, indirect contact, meal sharing, and lavatory co-usage were not independently associated with SARS-CoV-2 transmission.
Interpretation: Targeted community measures should include physical distancing and minimising verbal interactions. Testing of all household contacts, including asymptomatic individuals, is warranted.
Funding: Ministry of Health of Singapore, National Research Foundation of Singapore, and National Natural Science Foundation of China.