Background: Measles is a highly contagious viral illness and globally, 142,300 people died from measles in 2018. On 25 March 2021, an outbreak of measles was reported from Guradamole district Bale Zone Southeast Ethiopia. Hence, we investigated to determine existence of the outbreak and to identify the associated factors. Method: Descriptive and 1:2 unmatched case–control study was done in Guradamole district from March 25 to April 9/2021. For the descriptive study, a total of 98 cases were used. To identify the factor associated with the outbreak, 60 cases were selected by computer-generated simple random method by using line list as a sampling frame and 120 controls were studied. Active cases were identified through home-to-home searching in affected kebeles and controls were selected from neighbors of cases. Five serum samples were taken and an IgM test was done to confirm cases. Cases were any person who developed fever, maculopapular rash and cough, coryza or conjunctivitis while controls were without such diagnosis. We collected data by using a structured questionnaire, cases were described by time, place, and person; logistic regression was used to identify factors associated with measles. In the multivariable analysis P-value <0.05 was declared statistical significance. Results: Overall, 98 cases were identified with an overall attack rate of 12/1000 population and a case fatality rate (CFR) of 7%. The highest attack rate (38/1000 population) and CFR (57%) were among children aged <59 months. Vaccination efficacy was calculated to be 82.6%. Being unvaccinated (adjusted odds ratio/AOR=5.66, 95% confidence interval, CI: 1.24–25.81), contact with patient (AOR=3.24, 95%CI: 1.03–10.17), moderate malnutrition (AOR=4.34, 95%CI: 2.14–8.814), distance from health facility (AOR=4.58, 95%CI: 1.39–15.19) and history of travel to affected area (AOR=3.99, 95%CI: 1.31–12.19) were shown significant associated with measles infection. Conclusion: The attack and fatality rate of the investigation were high. Being unvaccinated, distant from the health facility, malnutrition, and history of contact with measles case were associated with the outbreak. We recommend conducting vaccination campaigns, interventions to malnutrition, and strengthening routine immunization programs to reduce future measles outbreaks.
