A total of 1,735 measles cases were included in the study. Among these, 1,387 (80%) were recorded by case-based and 348 (20%) were registered by line list. The majority (30%) of the cases occurred in 2015 followed by 417 (24%) in 2014.
During 2011-2015, most of the cases occurred in children age less than 15 years old (87%), and 33% were under five. Laboratory specimen was collected from 1399 cases and 93% were considered as an adequate sample. Among the total cases, 302 (17%) were confirmed by the laboratory, 349 (20%) were epidemiologically linked to laboratory-confirmed cases, 973 (56%) were discarded and 111 (6%) were compatible cases. Confirmed measles cases were 8 (4%) cases in 2012 and 339 (65%) cases in 2015 among the total cases in each year.
Of the total cases, 146 (8.4%) had missing values for the age variable. The age of laboratory-confirmed cases ranged from two months to 36 years old. Among those 1,589 measles cases fully documented for age, 846 (53.2%) were children 5-14 years of age, while 397 (25.0%), 134 (8.4%), and 212 (13%) were children 1-4 years, children less than 1 year and adults greater than or equal to 15 years old respectively (Fig.1).
Concerning vaccination status 374 (22%) of the cases were unvaccinated and 989 (57%) of the cases had an unknown status for measles vaccination. Of 651 total confirmed cases, 225 (35%) were unvaccinated and 298(46%) had unknown vaccination status for measles vaccination.
The administrative routine measles vaccine coverage for eligible children was 100% except in 2012 which was 95%. The number of children susceptible to measles was 563 (1%) in 2011 and 11637 (15%) in 2015 among those vaccines eligible in each year and totally within five years cumulative of 24,750 children’s were susceptible to measles. These included unvaccinated surviving infants and 15% of children from those vaccinated because of lack of seroconversion at nine months of age.
Thirteen out of fifteen districts in the zone reported measles cases. There were no reported cases from Arsi Negelle Town and Bishan Guracha districts. Among the total cases within five years, more than half (52.2%) of the cases were recorded in three districts; namely Shashemene, Kore, and Seraro accounting for 382(22.0%), 336 (19.4%), and 197(11.4%) cases respectively. The districts with the highest incidence rates included Wondo (115/100,000) in 2015, Kore (72/100,000) in 2013, and Shashemene (54/100,000) in 2011.
Measles cases were reported every month, and March had the highest number of cases (24%). A high proportion of the cases, 1215 (70%), developed the disease from January through June in five years. A small proportion of cases, 60 (3.0%) were recorded in December (Fig.2).
Based on the national measles guideline definition for the outbreak, there were 33 laboratory-confirmed outbreaks of measles in districts of the West Arsi Zone. Five Districts namely: Shashemene, Arsi Negelle, Dodola, Gedeb Assasa, and Kore accounted for 63.6% of the outbreak. The largest outbreak, 14 (42%), was occurring in 2015 and it affected 10 (67%) districts of the West Arsi Zone. The annual average measles incidence rate during 2011-2014 was 3.4/100,000 while the incidence rate in 2015 was 14/100,000 (Fig.3).
During 2011-2015, the most frequently affected districts include Shashemene which attacked five times; and Kore, Arsi Negele, Dodola, and Gedeb Asesa each was attacked four times. There were no SIAs done in 2014 and 2015. Regarding the seasonal variation of the outbreak, the highest proportion, 9 (27.3%), occurred in January followed by February 7(21.2%) and September 4 (12.1%).
Surveillance indicators
The proportion of districts that detected two and more cases of non-measles febrile rash per 100,000 populations in a year (annual detection rate for non-measles febrile rash) were 8(62%) in both 2011 and 2012, 10(92%) in 2013 and 10(67%) both in 2014 and 2015. The proportion of districts investigated greater than two suspected cases of measles with blood specimen per 100,000 populations per year (annualized rate of investigation) were 8 (62%) both in 2011 and 2012, 11 (85%), 11(73%), and 12(80%) from 2013 to 2015 respectively. There were no measles cases reported and investigated cases from Arsi Nagele Town and Bishan Guracha districts in 2014 and 2015.
The adequacy rate of specimens collected for laboratory tests was 92%, 100%, 80%, and 87% from 2012 up to 2015 respectively and it was 69% in 2011.