Measles Outbreak Investigation in Ginnir District of Bale Zone, Oromia Region, Southeast Ethiopia, May 2019

  • Vaccine preventable diseases
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Background:
Measles is vaccine-preventable viral infection of humans, primarily affecting children<5 years. During early 2019, outbreak of measles occurred in Ginnir district of Bale zone, Southeast Ethiopia. We investigated to describe the outbreak and identify risk factors.
Methods:
We conducted a descriptive and 1:2 unmatched case-control study in Ginnir district from March 18 to April 29, 2019. Fifty-six cases and 112 neighborhood controls were recruited. For descriptive study, we identified 1043 cases recorded on the line-list and for case-control study, cases were identified using active case search. Suspected measles cases were defined as any person with fever and maculopapular rash and cough, coryza or conjunctivitis. Confirmed case is a suspected case with positive IgM antibody. Mothers of case-patients and controls were interviewed using structured questionnaire. We estimated vaccination coverage (VC) and vaccine efficacy (VE) in children aged 9–59 months from case-control study. We conducted bivariate and multivariable logistic regression.
Results:
In four-months period, a total of 1,043 suspected measles cases epidemiologically linked to five laboratory confirmed cases reported from Ginnir district. Of which, 555(53.2%) were males and 714 (68.5%) were <5 years. The median age of cases was 36 months (IQR=12-60 months). The overall attack rate (AR) was 63/10,000 population with case fa- tality ratio of 0.5% (5 deaths/1043). Children <1 year (182/1043) were the most affected age groups (AR=34.3/1000), of which 150(82.4%) were not vaccinated against measles, while 27 (18%) were eligible for vaccination (9-11 months). From the total measles cases, 824(79%) were not vaccinated against measles. Last-year (2017/18) administrative measle vaccine coverage of the district was 76.7%. The last four years (2015-2018) immunization coverage data suggests there is a pool of susceptible population. Being unvaccinated against measles (AOR=5.4, 95%CI=2.2-13.4), travel history (AOR=4.02, 95%CI=1.2-13.6), contact with measles case-patient (AOR=5.6, 95%CI=2.12-14.4) and moth- ers knowledge of measles transmission (AOR=0.36, 95%CI=0.15-0.87) were associated with measles infection. VE was 90% (95%CI=69-97%). The estimated measles vaccination coverage was 65.7% (95%CI: 54.4–76.7%).
Conclusion
This confirmed measles outbreak was caused by failure to vaccinate, as indicated by the high VE, low administrative coverage, 79% unvaccinated cases and pool of susceptible population. Strengthening routine and supplementary immunization are required.

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