ABSTRACT
A long-standing question in infectious disease dynamics is the role of transmission heterogeneities, particularly those driven by demography, behavior and interventions. Here we characterize transmission risk between 1,178 SARS-CoV-2 infected individuals and their 15,648 close contacts based on detailed contact tracing data from Hunan, China. We find that 80% of secondary transmissions can be traced back to 14% of SARS-CoV-2 infections, indicating substantial transmission heterogeneities. Regression analysis suggests a marked gradient of transmission risk scales positively with the duration of exposure and the closeness of social interactions, after adjusted for demographic and clinical factors. Population-level physical distancing measures confine transmission to families and households; while case isolation and contact quarantine reduce transmission in all settings. Adjusted for interventions, the reconstructed infectiousness profile of a typical SARS-CoV-2 infection peaks just before symptom presentation, with ~50% of transmission occurring in the pre-symptomatic phase. Modelling results indicate that achieving SARS-CoV-2 control would require the synergistic efforts of case isolation, contact quarantine, and population-level physical distancing measures, owing to the particular transmission kinetics of this virus.
ABSTRACT
BackgroundSeveral parameters driving the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remain unclear, including age-specific differences in infectivity and susceptibility, and the contribution of inapparent infections to transmission. Robust estimates of key time-to-event distributions remain scarce as well. MethodsWe collected individual records for 1,178 SARS-CoV-2 infected individuals and their 15,648 contacts identified by contact tracing and monitoring over the period from January 13 to April 02, 2020 in Hunan Province, China. We provide descriptive statistics of the characteristics of cases and their close contacts; we fitted distributions to time-to-key-events distributions and infectiousness profile over time; and we used generalized linear mixed model to estimate risk factors for susceptibility and transmissibility of SARS-CoV-2. ResultsWe estimated the mean serial interval at 5.5 days (95%CI -5.0, 19.9) and the mean generation time at 5.5 days (95%CI 1.7, 11.6). The infectiousness was estimated to peak 1.8 days before symptom onset, with 95% of transmission events occurring between 7.6 days before and 7.3 days after the date of symptom onset. The proportion of pre-symptomatic transmission was estimated to be 62.5%. We estimated that at least 3.5% of cases were generated asymptomatic individuals. SARS-CoV-2 transmissibility was not significantly different between working-age adults (15-59 years old) and other age groups (0-14 years old: p-value=0.16; 60 years and over: p-value=0.33), whilst susceptibility to SARS-CoV-2 infection was estimated to increase with age (p-value=0.03). In addition, transmission risk was higher for household contacts (p-value<0.001), decreased for higher generations within a cluster (second generation: odds ratio=0.13, p-value<0.001; generations 3-4: odds ratio=0.05, p-value<0.001, relative to generation 1), and decreased for infectors with a larger number of contacts (p-value=0.04). InterpretationOur findings warn of the possible relevant contribution of children to SARS-CoV-2 transmission. When lockdown interventions are in place, we found that odds of transmission are highest in the household setting but, with the relaxation of interventions, other settings (including schools) could bear a higher risk of transmission. Moreover, the estimated relevant fraction of pre-symptomatic and asymptomatic transmission highlight the importance of large-scale testing, contact tracing activities, and the use of personnel protective equipment during the COVID-19 pandemic.
ABSTRACT
Objective To estimate the serotype and age-specific hospitalization burden associated with hand,foot and mouth disease (HFMD) in Anhua county of Hunan province,between October 2013 and September 2016.Methods We collected hospitalization records of HFMD patients from 6 virological surveillance hospitals,and reimbursement records through new rural cooperative medical system from 23 township health centers to estimate the age-specific hospitalization burden of HFMD in Anhua.Combined with the results of virological surveillance,the serotype-specific hospitalization burden of HFMD in Anhua,was estimated.Results During the three years,it was estimated that 3 541 clinical diagnosed HFMD cases,including 3 146 laboratory-confirmed HFMD cases,were hospitalized in Anhua,but only one was diaguosed as being severe.The estimated average hospitalization rate was 723/100 000(95％C1:699/100 000-747/100 000) for clinical diagnosed HFMD and 642/100 000 (95％ CI:620/100 000-665/100 000) for laboratory-confirmed HFMD between October 2013 and September 2016.The cases caused by Cox A16 (208/100 000) and Cox A6 (202/100 000) had higher hospitalization rates compared with the cases caused by EV71 (130/100 000),Cox A10 (38/100 000) and other enterovirus (64/100 000),and the difference was statistically significant (P＜0.001).HFMD-associated hospitalization rates peaked in children aged 1 year (3 845/100 000),and then decreased with age.Compared with the hospitalized HFMD caused by EV71 and Cox A16,Cox A6-associated hospitalizations mainly occurred in younger age groups (P＜0.001).Conclusion Our study revealed a substantial hospitalization burden associated with mild HFMD caused by EV71,Cox A16,Cox A6 and Cox A10,especially in young children,in Anhua.
ABSTRACT
Objective To estimate the serotype and age-specific hospitalization burden associated with hand,foot and mouth disease (HFMD) in Anhua county of Hunan province,between October 2013 and September 2016.Methods We collected hospitalization records of HFMD patients from 6 virological surveillance hospitals,and reimbursement records through new rural cooperative medical system from 23 township health centers to estimate the age-specific hospitalization burden of HFMD in Anhua.Combined with the results of virological surveillance,the serotype-specific hospitalization burden of HFMD in Anhua,was estimated.Results During the three years,it was estimated that 3 541 clinical diagnosed HFMD cases,including 3 146 laboratory-confirmed HFMD cases,were hospitalized in Anhua,but only one was diaguosed as being severe.The estimated average hospitalization rate was 723/100 000(95％C1:699/100 000-747/100 000) for clinical diagnosed HFMD and 642/100 000 (95％ CI:620/100 000-665/100 000) for laboratory-confirmed HFMD between October 2013 and September 2016.The cases caused by Cox A16 (208/100 000) and Cox A6 (202/100 000) had higher hospitalization rates compared with the cases caused by EV71 (130/100 000),Cox A10 (38/100 000) and other enterovirus (64/100 000),and the difference was statistically significant (P＜0.001).HFMD-associated hospitalization rates peaked in children aged 1 year (3 845/100 000),and then decreased with age.Compared with the hospitalized HFMD caused by EV71 and Cox A16,Cox A6-associated hospitalizations mainly occurred in younger age groups (P＜0.001).Conclusion Our study revealed a substantial hospitalization burden associated with mild HFMD caused by EV71,Cox A16,Cox A6 and Cox A10,especially in young children,in Anhua.
