A hospital-related outbreak of SARS-CoV-2 associated with variant Epsilon (B.1.429) in Taiwan: transmission potential and outbreak containment under intensified contact tracing, January-February 2021

Abstract

Objectives: A hospital-related cluster of 22 cases of coronavirus disease 2019 (COVID-19) occurred in Taiwan in January-February 2021. Rigorous control measures were introduced and could only be relaxed once the outbreak was declared over. Each day after the apparent outbreak end, we estimated the risk of future cases occurring in order to inform decision-making.

Methods: Probabilistic transmission networks were reconstructed, and transmission parameters (the reproduction number R and overdispersion parameter k) were estimated. The reporting delay during the outbreak was estimated (Scenario 1). In addition, a counterfactual scenario with less effective interventions characterized by a longer reporting delay was considered (Scenario 2). Each day, the risk of future cases was estimated under both scenarios.

Results: The values of R and k were estimated to be 1.30 ((95% credible interval (CI) 0.57-3.80) and 0.38 (95% CI 0.12-1.20), respectively. The mean reporting delays considered were 2.5 days (Scenario 1) and 7.8 days (Scenario 2). Following the final case, ttthe inferred probability of future cases occurring declined more quickly in Scenario 1 than Scenario 2.

Conclusions: Rigorous control measures allowed the outbreak to be declared over quickly following outbreak containment. This highlights the need for effective interventions, not only to reduce cases during outbreaks but also to allow outbreaks to be declared over with confidence.

Keywords: COVID-19; End-of-outbreak declaration; Epidemic modelling; SARS-CoV-2.

Figure 1

Timeline of exposure and possible connections between reported cases. Connections shown here were determined either by identifying the most probable infector via epidemiological investigation, or by the earliest time of symptom onset among all close contacts if the most likely pair could not be determined (such as in family clusters of B1.2, C1.1 and B4.1).

Figure 2

The estimated risk of cases being reported in future for Scenario 1 (under intensified contact tracing; green) and Scenario 2 (less rigorous public health measures; black). Bars in orange indicate the incidence of SARS-CoV-2 infections by confirmation date.