Timeliness of contact tracing among flight passengers during the COVID-19 epidemic in Vietnam

Abstract

Background: International air travel plays an important role in the global spread of SARS-CoV-2, and tracing of close contacts is an integral part of the public health response to COVID-19. We aimed to assess the timeliness of contact tracing among airline passengers arriving in Vietnam on flights containing COVID-19 cases and investigated factors associated with timeliness of contact tracing.

Methods: We included data from 2228 passengers on 22 incoming flights between 2 and 19 March 2020. Contact tracing duration was assessed separately for the time between the date of index case confirmation and date of contact tracing initiation (interval I), and the date of contact tracing initiation and completion (interval II). We used log-rank tests and multivariable Poisson regression models to identify factors associated with timeliness.

Results: The median duration of interval I and interval II was one (IQR: 1-2) and 3 days (IQR: 2-5), respectively. The contact tracing duration was shorter for passengers from flights where the index case was identified through mandatory testing directly upon arrival (median = 4; IQR: 3-5) compared to flights with index case detection through self-presentation at health facilities after arrival (median = 7; IQR: 5-8) (p-value = 0.018). Cumulative hazards for successful tracing were higher for Vietnamese nationals compared to non-Vietnamese nationals (p < 0.001).

Conclusions: Contact tracing among flight passengers in the early stage of the COVID-19 epidemic in Vietnam was timely though delays occurred on high workload days. Mandatory SARS-CoV-2 testing at arrival may reduce contact tracing duration and should be considered as an integrated screening tool for flight passengers from high-risk areas when entering low-transmission settings with limited contact tracing capacity. We recommend a standardized risk-based contact tracing approach for flight passengers during the ongoing COVID-19 epidemic.

Keywords: COVID-19; Contact tracing; SARS-CoV-2; Timeliness; Vietnam.

Fig. 1

Procedure of contact tracing for flights with COVID-19 infected cases in Vietnam. ^* Direct contact information: email, telephone, social media accounts. ^** Indirect information: residential address, workplace address, tourism company. ^*** Supplementary information: temporary/permanent residential registration at local authorities, police department records, tour registration at tourism bureaus, relevant embassies, and immigration bureau data

Fig. 2

Contact tracing outcomes of 22 flights with infected COVID-19 cases during March 2020 in Vietnam

Fig. 3

Number of passengers needed to be traced, successfully traced, and not yet successfully traced^* each day. ^*Number of passengers not yet successfully traced = number of passengers needed to be traced – number of passengers successfully traced. Number of passengers needed to be traced at each day = number of passengers not yet succesfully traced from previous day(s) + new number of passenger needed to be traced. Note: We excluded index cases and transited passengers from this analysis since we did not attempt to trace them

Fig. 4

The cumulative probability of unsuccessful tracing for 1812 passengers on 22 flights during March 2020. * Survival probability was estimated using Kaplan Meier and interpreted as probability of successful tracing. Note: Dotted red lines indicated the 95% confidence intervals. The black dashed line indicates the time when half of all passengers are expected to be traced

Fig. 5

Cumulative hazard of successful tracing for passengers by method of index case detection (a) and nationality of passengers (b). * Cumulative hazards were estimated using Kaplan Meier and interpreted as probability of successful trace. p-value was calculated from log-rank tests. Note: Dotted lines indicated the 95% confidence intervals