Measles Outbreak in Kamukunji Sub-County, Nairobi County - Kenya, 2018

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In early 2018, measles outbreaks began in rural Kenya. In August 2018, cases were laboratory-confirmed in urban Kamukunji Sub-county, home to a large migrant, refugee population, with first-dose measles containing vaccine (MCV1) and second-dose measles containing vaccine (MCV2) coverage of 73% and 35% respectively in 2017. We conducted an epidemiologic investigation to inform control efforts.
We reviewed health facility registers and interviewed community health workers regarding sick children residing near confirmed cases, including a boarding school. A suspected case was an illness with fever, maculopapular rash, and cough, coryza or conjunctivitis or one where a clinician suspected measles, in any person living or visiting Kamukunji during January 1–October 3, 2018. A confirmed case was measles immunoglobulin M (IgM) antibody positive, not induced by vaccination; epidemiologically linked to a laboratory-confirmed case without specimen; or clinically compatible without epi-linkage or adequate specimen collected. We interviewed cases or their guardians using a structured questionnaire. We collected serum samples for IgM antibody detection by enzyme-linked immunosorbent assay (ELISA) and nasopharyngeal samples for measles virus RNA detection by real-time polymerase chain reaction (RT-PCR) and genotyping by sequencing the detected virus. We calculated descriptive statistics and attack rates by various categories.
During January–October, 2018, we identified 67 confirmed cases [52 (78%) epi-linked and 15 (22%) laboratory- confirmed]; 28 (42%) from the community and 39 (58%) from health facilities. Of the confirmed cases, 43 (64%) were male; 39 (58%) were aged <5 years and 10 (15%) were aged <9 months (range: 3 months–19 years). The highest attack rate was 15 per 10,000 in children <1 year. Only 15 (28%) of 53 cases eligible for MCV1 had received it; and only nine (29%) of 31 cases eligible for MCV2 had received it. Of 16 blood samples collected, 10 (63%) were positive for measles IgM antibodies. Measles virus genotype B3 was detected in five (71%) of 7 nasopharyngeal samples collected.
This outbreak occurred among under-vaccinated children in an urban sub-county. Children aged <1 year had highest attack rates, illustrating the importance of providing two doses of MCV to eligible children in order to protect those most vulnerable.

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