Background: Measles is vaccine-preventable viral infection of humans, primarily affecting children under 5 years. During September 2019, outbreak of measles occurred in Gemechis district of West Hararghe zone, Eastern Ethiopia. This study aimed to describe the magnitude of measles outbreak and identify risk factors for measles infection in Gemechis district, West Hararghe zone, Eastern Ethiopia, from 03-12/01/2020.

Methods: We conducted a descriptive and 1:2 unmatched case-control study in Gemechis district from January 03 -12, 2020. Fifty cases and 100 neighborhood controls were recruited for case control study. For descriptive study, we identified 169 cases recorded on line-list and, for case-control study; cases were identified using national standard case-definition and active case search. Mothers of case-patients and controls were interviewed using a structured questionnaire. We estimated sample size using OpenEpi for unmatched case-control study. We conducted bivariate and multivariable logistic regression. Multi-colinearity was checked between travel and contact history.

Results: A total of 164 suspected measles cases which epidemiologically linked to five confirmed cases were reported from Gemechis district. Of which, 95(56.21%) were males and, 86(51%) were under 5 years. The overall attack rate (AR) was 7/10,000 population with case fatality ratio of 1.18% (2 deaths/169). Children age group 1-4 year (83/169) were the most affected age groups (AR=26/10,000). From the total measles cases, 127(75.15%) were not vaccinated against measles. Being unvaccinated against measles [AOR=4.45, 95% CI=1.43-13.98, P=0.01], Mothers/ Care taker knowledge level of measles [AOR= 3.35, 95% CI=1.23-12.08, P=0.02], Travel history to measles area [AOR =5.02, 95% CI = 1.38 -18.31, P= 0.01] and Contact with measles patient [AOR=5.31, 95% CI = 1.53- 18.44, P= 0.01] were associated with measles infection.

Conclusion: Low vaccination coverage among cases was likely contributed to the outbreak and being unvaccinated, having travel history to area with active measles, having contact with measles cases, and knowledge of caregivers on measles were independently associated with measles infection. Strengthening routine and supplementary immunization and awareness creation activities strongly recommended.

Key Words: Measles, outbreak, investigation, risk factors, case control