# Incidence and predictors of Sudan ebolavirus transmission among contacts in Uganda in 2022: a retrospective cohort study

## TL;DR

This study analyzed how Sudan ebolavirus spread among contacts in Uganda in 2022, finding higher transmission in secondary settings and beyond the standard 21-day monitoring period.

## Contribution

The study provides new insights into the incidence and risk factors for Sudan ebolavirus transmission during the 2022 Uganda outbreak.

## Key findings

- The incidence rate of Sudan ebolavirus was 1.6 cases per 1,000 person-days of follow-up.
- Secondary transmission settings had an 81% higher incidence than primary settings.
- High-risk contact status and male sex in secondary settings were significant predictors of transmission.

## Abstract

Ebola disease (EBOD) is a highly lethal zoonotic viral hemorrhagic fever that is responsible for 41 outbreaks globally. Ebola transmission is a key driver of the magnitude and complexity of outbreaks, yet incidence rate during outbreaks is not fully studied. This study aimed to determine the incidence and predictors of Sudan Ebolavirus transmission during the 2022 outbreak in Uganda.

We conducted a retrospective cohort study leveraging surveillance records for individuals identified as contacts, and collected between September and December 2022 during the Sudan Ebolavirus Disease (SUVD) outbreak in Uganda. Data were extracted and analyzed via Stata/SE 15. This analysis involved calculating incidence rates and assessing predictors of Ebola transmission through appropriate multivariable regression models, and controlling for potential confounders like sex, age, health worker, and place of contact. The study protocol was approved by the Busitema University Research Ethics Committee (BUFHS-2023-145). Individual informed consent was waived, and all the data were anonymized.

3140 contacts were included in the study, with 50.6% being female and a mean age of 24 years. The incidence rate of SUVD was 1.6 cases per 1,000 person-days of follow-up. Kaplan Meier survival function showed that the risk for being diagnosed with SUVD extended beyond 21 days, up to the 28th day postexposure. The incidence of SUVD in secondary transmission settings was 1.8 times higher than that in primary transmission settings (IRR = 1.81, 95% CI = 1.202–2.735; P < 0.001). After controlling for sex, age, health worker, and place of contact, the significant predictors of SUVD transmission were high-risk contact status (aHR = 2.5, 95% CI: 1.68–3.72; P < 0.001) and male sex in secondary transmission settings (aHR = 2.14, 95% CI = 1.15–4.01; P = 0.02).

This study revealed a high incidence of Ebola among contacts, with cases emerging beyond the standard 21-day follow-up period. The incidence was notably higher in secondary transmission settings, with high-risk contacts and males being particularly vulnerable. These findings suggest the need to revise contact tracing protocols (extend beyond 21 days), and prioritize follow-up on the basis of risk stratification. Further research is warranted to explore sex-related differences in secondary transmission dynamics.