Epidemiologic Characteristics, Transmission Chain, and Risk Factors of Severe Infection of COVID-19 in Tianjin, a Representative Municipality City of China

Abstract

This study was performed to describe the epidemiologic characteristics of coronavirus disease 2019 (COVID-19) and explore risk factors for severe infection. Data of all 131 confirmed cases in Tianjin before February 20 were collected. By February 20, a total of 14/16 districts reported COVID-19 cases, with Baodi district reporting the most cases (n = 56). A total of 22 (16.8%) cases had a Wuhan-related exposure. Fever was the most common symptom (82.4%). The median duration of symptom onset to treatment was [1.0 (0.0-4.0) days], the duration of symptom onset to isolation [2.0 (0.0-6.0) days], and the duration of symptom onset to diagnosis [5.0 (2.0-8.0) days]. The analysis of the transmission chain showed two cluster infections with 62 cases infected. Transmission from a family member constituted 42%, usually at the end of transmission chain. Compared with patients with non-severe infections, patients with severe infections were more likely to be male (46.2 vs. 77.3%, P = 0.009) and had a Wuhan-related exposure (14.0 vs. 40.9%, P = 0.004). Multivariate logistic regression showed that male (OR 3.913, 95% CI 1.206, 12.696; P = 0.023) was an independent risk factor for severe infection. This study provides evidence on the epidemic of COVID-19 by analyzing the epidemiological characteristics of confirmed cases in Tianjin. Self-quarantine at an outbreak's early stage, especially for those with high-risk exposures, is conducive to prevent the transmission of infection. Further investigation is needed to confirm the risk factors for severe COVID-19 infection and investigate the mechanisms involved.

Keywords: SARS-CoV-2; coronavirus disease 2019; epidemiologic characteristics; gender; risk factors; transmission chain.

Figure 1

Temporal distribution of confirmed COVID-19 cases in Tianjin. Epidemic curves of confirmed cases were drawn according to the date of onset and the date of diagnosis (A). The distribution of cases was plotted based on specific duration since the onset date of symptoms (B).

Figure 2

Spatial distributions of confirmed COVID-19 cases in Tianjin. Daily number of new infections in each district (A) and cumulative number of cases on map by the end of January 21, 2020, January 31, 2020, February 10, 2020, and February 20, 2020 (B).

Figure 3

Transmission chain for the 131 confirmed COVID-19 cases in Tianjin. Red figures indicate a Wuhan-related exposure. Gray solid fill represents severe case. Numbers in dashed circle (lower right corner) represent the total number of unrelated independent events, and these patients did not transmit the virus to others. The blue hollow ring in the lower right corner indicates that these patients were infected at the same time or from the same source, for example, #14, #25, #54, and #59 traveled to Wuhan together.