Risk factors for diphtheria in Sana'a, Yemen, 2019: a matched case–control study

OBJECTIVE: To identify risk factors for diphtheria related to sociodemographic, immunization and household status, and source of infection in Sana'a. METHODS: A retrospective matched case–control study (1:2 ratio) was conducted. Cases were defined as patients who met the World Health Organization's definition of confirmed diphtheria living in Sana'a between January and November 2019. Controls were defined as subjects without a history of diphtheria infection, living in the same neighbourhood, and matched with cases by age and sex. Crude odds ratios, adjusted odds ratio (aOR) and 95% confidence intervals (CI) were calculated to evaluate associations between risk factors and diphtheria. RESULTS: In total, 76 confirmed cases and 152 controls were enrolled in this study. Multi-variate analysis found significant associations between diphtheria infection and sharing a bedroom with at least two people (aOR 2.8, 95% CI 1.2–6.6), non-vaccination (aOR 2.6, 95% CI 1.2–6.0) and contact with a diphtheria case (aOR 10.6, 95% CI 2.6–43.6). CONCLUSIONS: This study found that vaccination, not sharing a bedroom with at least two people, and isolation of diphtheria cases to prevent contact with non-infected individuals were the most important measures for protection of the community from diphtheria. Raising community awareness about vaccination, transmission and preventive measures is recommended.