Risk factors of diphtheria outbreak in damt district of Al Dhalea Governorate, 2023 -Yemen: a case-control study.

Background: In Yemen, diphtheria has become an important health problem since 2017 when diphtheria re-emergence as a consequence of war and the collapse of the health system. In 2023, there has been a 57% increase in diphtheria cases compared to 2021 and 2022. Damt district of Al Dhalea Governorate had the highest reported cases for year 2023. The study aims to determine the risk factors associated with diphtheria outbreak in Damt District.

Methods: A retrospective matched case-control (1:2) was used. All confirmed cases based on the WHO case definition reported from Damt district during 2023 were considered cases. Two age-matched (± 5years) neighborhood controls were recruited per case. A pretested questionnaire was used for collecting data during household interviews including demographic and household characteristics, knowledge of diphtheria, vaccination status, contact with a case of diphtheria, and travel history. Frequency and proportion for quantitative and median with interquartile range (IQR) for quantitative variables. Chi-square and Mann-Whitney tests to compare the distribution of categorical and numerical variables between cases and controls. Univariate and multivariate conditional binary logistic regression, and Adjusted Odds ratio (AOR) with a 95% confidence interval at P < 0.05 were used to identify risk factors.

Results: A total of 118 cases and 236 controls were enrolled, 56% were females (63% of cases vs. 53% of controls). The median (IQR) age was 14 (9,22) years for cases vs 12(7,23) of control, it was significantly higher for females than males in the case group: (16(10,29) Vs 10(6,18), P < 0.001) and control group: (15(8,25) vs 12(7,18), p-value = 0.022). Partial vaccination status AOR = 13.7(6.1-31.1), P-value < 0.001), contacts with a case of diphtheria AOR = 8.5(2.3-31.0), P value < 0.001) and Female gender, AOR = 3.3(CI; 1.1-9.5, P value = 0.029), were the main risk factors.

Conclusions: Poor vaccination and contact with a case of diphtheria were the main contributors to diphtheria in the Damt district particularly among adult females. Increasing the vaccination coverage with a diphtheria-containing vaccine through routine immunization as well as tetanus-diphtheria vaccine for childbearing age females along with community awareness regarding protection measures during home care of diphtheria cases. Vaccination services as well as gender barriers related to Td vaccination should be investigated.