Being unvaccinated and having a contact history increased the risk of measles infection during an outbreak: a finding from measles outbreak investigation in rural district of Ethiopia

Background: Measles is one of the most contagious diseases caused by an acute viral illness called Morbillivirus that usually occurs as an outbreak in low-income countries. As of May 2016 measles suspected outbreak was reported from Sekota Zuria district. We investigated the outbreak to identify its possible sources and risk factors of acquiring the infection in the district.

Method: We conducted a 1:2 unmatched case-control study in May 2016 in Sekota Zuria district, Northern Ethiopia. Cases involved in the study were lab confirmed and epidemiologically linked. Controls were those who had no clinical signs of measles and residing in the same communities where the cases were identified. An interviewer-administered questionnaire was used to collect the data. Data were cleaned and entered to Epi-info7 and analyzed using SPSS-20. A logistic regression analysis was conducted to identify risk factors associated with measles infection at a p-value ≤0.05.

Results: 29 cases were identified during the outbreak investigation. The probable source of an outbreak was an index case who had a travel history to a district with a measles epidemic. Five samples were collected for confirmation of the diagnosis. No measles-related deaths were reported. The median age of cases and controls was 15 years (SD ± 7.8) and 11 years (SD ± 9.8), respectively. More than 55% of the cases were in age ≥ 15 years. In the multivariable analysis, being previously vaccinated for measles reduced the risk of measles infection by 83% (AOR, 95%CI = 0.17, 0.05-0.53) and having a contact history increased the risk of measles infection by 3.44 times (AOR, 95%CI = 3.44, 1.26-9.38).

Conclusion: We confirmed a measles outbreak in Sekota Zuria district. The majority of the cases were in age ≥ 15 years. Being un-vaccinated and having a contact history with confirmed or suspected cases were increased the risk of measles infection. To catch up with missed children at the time of the first dose of measles vaccine and reduce their susceptibility, supplementary immunization activities (SIAs) or immunization campaigns shall be strengthened.