Transmission Dynamics and Contact Tracing Assessment of COVID-19 in Chattogram, Bangladesh and Potential Risk of Close Contacts at Different Exposure Settings

Abstract

Background: Given the limited understanding of the behaviors of the virus it is crucial to decipher the transmission dynamics for the development of strategic plans and evaluation of effective control measures. We aimed to estimate the key components of disease transmission and secondary attack rate from different exposure settings and highlight the measures of control of the virus.Methods: In this study, we used COVID-19 symptomatic surveillance cases and their close contacts from April 3 to June 2, 2020. From this pool of cases, we compared the time from symptom onset and serial intervals. We also estimated disease transmission in different exposure settings and factors leading to transmission risk.Findings: The mean age was 41.5 years, including 159 (87.85%) of males and 22 (12.15%) females. At the initial case assessment, 53 (29.28%) were mild, 114 (62.30%) were moderate and 14 (7.7%) were severe cases. The median time to recovery was 21.09 days (95% CI 19.44-22.9). The crude case fatality rate amongst all cases was 6.08% (95% CI 4.62-7.54), relatively higher in age over 60 (17.78, 95% CI 14.85-20.70). Patients who were admitted to hospitals were treated with intravenous fluids and antibiotics and severe cases were given supplemental oxygen therapy. Median time from symptom onset to death was 15.7 days (95% CI 13.83-17.91). Among 319 close contacts, there were 13 secondary cases having an overall secondary attack rate of 4.08 (95% CI 1.95-6.20). The secondary attack rate among household contacts was at the highest risk of attack (13.04%, 95% CI 9.67-16.41) followed by funeral ceremonies (8.33%, 95% CI 3.99-12.66) and family contacts (6.52%, 95% CI 4.02-9.02). The attack rate was higher in age groups 50-59 (10.89%, 95% CI 7.05-14.66) and 60-69 (9.09%, 95% CI 5.08-13.09).Interpretation: Considering the demographic interactions, our data on index cases as well as their close contacts suggest critical insights into the epidemiological characteristics of COVID-19. Our analyses suggest that prompt isolation, physical distancing and contact tracing of symptomatic cases significantly reduce the spread of virus and thereby reduce the overall secondary infection in the community.Funding Statement: This study was supported by Bangladesh Medical Research Council (BMDC).Declaration of Interests: The authors declare no competing interests.Ethics Approval Statement: This work was conducted as part of the ongoing public health response, therefore institutional or regional review board approval and individual cases consent approval was waived. This study was approved by ethics committee of the Bangladesh Medical Research Council (BMDC).