layout: true background-image: url(uga.png) background-size: 120px 120px background-position: top right --- class: middle, center # COVID-19 Transmission Dynamics Among Close Contacts # A Cohort Study Yang Ge November - 2021 --- # Introduction I am a doctoral candidate in Epidemiology and a master candidate in Biostatistics at the University of Georgia (will graduate in May 2022). --- # The Study Yang Ge, Leonardo Martinez, Shengzhi Sun, Zhiping Chen, Feng Zhang, Fangyu Li, Wanwan Sun, Enfu Chen, Jinren Pan, Changwei Li, Jimin Sun, Andreas Handel, Feng Ling, and Ye Shen. (2021). **COVID-19 Transmission Dynamics Among Close Contacts of Index Patients With COVID-19: A Population-Based Cohort Study in Zhejiang Province, China.** *JAMA Internal Medicine*. doi: https://doi.org/10.1001/jamainternmed.2021.4686 --- # Backgrounds + Late 2020 + SARS-CoV-2 caused millions disability and deaths. + No vaccines. + NPIs. However, when individuals with COVID-19 are most infectious during their disease process requires further elucidation. + Impact: 1. Cases: case management 1. Contacts: early finding 1. Authority: contact tracing --- # Key questions 1. Among contacts, infection risk comparisons between the timing of exposure 1. Among contacts, association between COVID-19 infection and index case's severity. 1. Among infected contacts, association between severity of COVID-19 disease and index case's severity. --- # Methods 1 + Study design: A cohort study of contacts of COVID-19 index patients. + COVID-19 cases and their contacts - Index patients: the first eligible patient with a diagnosed case of COVID-19 with 1 or more contacts. - Index patients recall recent contacts, after which those individuals were contacted. - contacts were quarantined for at least 14 days and received investigations. - All patients were followed up for at least 90 days to distinguish between asymptomatic and presymptomatic illness. - Among these patients, those who developed symptoms later received a final classification as symptomatic. Otherwise were classified as asymptomatic. --- # Methods 2 + Timing of exposure: the first day and duration of the social contact between index patients and their contacts. - index patient symptom onset and the reported exposure period (confirmed by both index patients and contacts) - the last day of exposure time was assigned as the last reported day of exposure by the index patient and contact - included only contacts whose exposure occurred between 14 days prior to and 10 days after the index patient’s symptom onset date - compared the risk of COVID-19 at different exposure days <img src="cnt.png" width="100%" style="display: block; margin: auto;" /> --- # Methods 3 + Contacts were included in this analysis if they had RT-PCR test result. + Only symptomatic index cases, as the start of index patient–contact exposure to asymptomatic index patients is unclear. + We compared timing of exposure between index patients and their contacts by single-day bins. <img src="cnt.png" width="70%" style="display: block; margin: auto;" /> --- # Methods 4 **Infection risk comparisons between the timing of exposure?** + The risk of COVID-19 was estimated for each single-day bin (from 14 days before index patient symptom onset to 10 days after index patient symptom onset). + The RR was estimated by the exposure-lag-response association in the distributed lag nonlinear models. - it was defined on a grid of values of the binary variable of exposure and a continuous variable of lag time (days). - if a contact was first exposed on the day of symptom onset of their index patient (day 0), the RR is derived by comparing the estimated risk of COVID-19 without exposure at the same day but with exposure at different time points. <img src="cnt.png" width="70%" style="display: block; margin: auto;" /> --- # Methods 5 **Association between COVID-19 infection and index case's severity?** - multilevel multivariable model adjusting for potential confounders. **Association between severity of COVID-19 disease and index case's severity?** - asymptomatic clinical presentation among infected contacts. - restricted only to contacts infected with COVID-19. - compared the risk of asymptomatic clinical presentation in infected contacts stratified by severity of the index patient’s COVID-19 case. - evaluated whether asymptomatic clinical presentation was associated with clinical index patient severity - multilevel multivariable model adjusting for potential confounders. --- # Results 1 <img src="flow.png" width="60%" style="display: block; margin: auto;" /> --- # Results 2 <img src="tab1a.png" width="70%" style="display: block; margin: auto;" /> --- # Results 3 <img src="tab1b.png" width="70%" style="display: block; margin: auto;" /> --- # Results 4 <img src="sf2.png" width="90%" style="display: block; margin: auto;" /> --- # Results 5 <img src="sf1.png" width="100%" style="display: block; margin: auto;" /> --- # Results 6 <img src="f2.png" width="100%" style="display: block; margin: auto;" /> --- # Results 7 <img src="f3a.png" width="80%" style="display: block; margin: auto;" /> --- # Results 8 <img src="f3b.png" width="80%" style="display: block; margin: auto;" /> --- # Findings 1 1). Among contacts, infection risk comparisons between the timing of exposure + contacts were at highest risk of COVID-19 if they were exposed between 2 days before and 3 days after the index patient’s symptom onset, peaking at day 0 (adjusted relative risk [ARR], 1.3; 95% CI, 1.2-1.5). --- # Findings 2 2). Among contacts, association between COVID-19 infection and index case's severity. + Compared with being exposed to an asymptomatic index patient, the risk of COVID-19 among contacts was higher when they were exposed to index patients with mild (ARR, 4.0; 95% CI, 1.8-9.1) and moderate (ARR, 4.3; 95% CI, 1.9-9.7) cases of COVID-19. --- # Findings 3 3). Among secondary infections, association between severity of COVID-19 disease and index case's severity. + As index case severity increased, infected contacts were less likely to be asymptomatic (exposed to patient with mild COVID-19: ARR, 0.3; 95% CI, 0.1-0.9; exposed to patient with moderate COVID-19: ARR, 0.3; 95% CI, 0.1-0.8). --- # Limitations + Directionality of transmission was identified by index patients’ recall and then determined based on the chronological order of symptom onset time + Not all contacts were traced and screened with RT-PCR testing + Nonpharmaceutical interventions were widely conducted that reduced transmission risk. --- # Acknowledge Leonardo Martinez, Shengzhi Sun, Zhiping Chen, Feng Zhang, Fangyu Li, Wanwan Sun, Enfu Chen, Jinren Pan, Changwei Li, Jimin Sun, Andreas Handel, Feng Ling, and Ye Shen --- class: middle, center # Thanks, questions? yang.ge@uga.edu https://yangepi.github.io/