Individual and household risk factors for Ebola disease among household contacts in Mubende and Kassanda districts, Uganda, 2022

Abstract Background: In 2022, a Sudan virus disease (SVD) outbreak occurred in Uganda, resulting in 142 confirmed cases, most in Mubende and Kassanda districts. We determined risk factors for Sudan virus (SUDV) infection among household members (HHM) of cases. Methods: We conducted a case-control and retrospective cohort study in January 2023. Cases were RT-PCR-confirmed SUDV infection in residents of Mubende or Kassanda districts during the outbreak. Case-households housed a symptomatic, primary case-patient for ≥24 hours and had ≥1 secondary case-patient with onset <2 weeks after their last exposure to the primary case-patient. Control households housed a case-patient and other HHM but no secondary cases. A risk factor questionnaire was administered to the primary case-patient or another adult who lived at home while the primary case-patient was ill. We conducted a retrospective cohort study among case-household members and categorized their interactions with primary case-patients during their illnesses as none, minimal, indirect, and direct contact. We conducted logistic regression to explore associations between exposures and case-household status, and Poisson regression to identify risk factors for SUDV infection among HHM. Results: Case- and control-households had similar median sizes. Among 19 case-households and 51 control households, primary case-patient death (adjusted odds ratio [ORadj]=7.6, 95% CI 1.4-41) and ≥2 household bedrooms (ORadj=0.19, 95% CI 0.056-0.71) were associated with case-household status. In the cohort of 76 case-HHM, 44 (58%) were tested for SUDV <2 weeks from their last contact with the primary case-patient; 29 (38%) were positive. Being aged ≥18 years (adjusted risk ratio [aRRadj]=1.9, 95%CI: 1.01-3.7) and having direct or indirect contact with the primary case-patient (aRRadj=3.2, 95%CI: 1.1-9.7) compared to minimal or no contact increased risk of SVD. Access to a handwashing facility decreased risk (aRRadj=0.52, 95%CI: 0.31-0.88). Conclusion: Direct contact, particularly providing nursing care for and sharing sleeping space with SVD patients, increased infection risk among HHM. Risk assessments during contact tracing may provide evidence to justify closer monitoring of some HHM. Health messaging should highlight the risk of sharing sleeping spaces and providing nursing care for persons with Ebola disease symptoms and emphasize hand hygiene to aid early case identification and reduce transmission.