Measles outbreak in Semuto Subcounty, Nakaseke District, Uganda, June-August 2021

Semuto Subcounty reported rubella/measles outbreaks in January 2020 and June-August 2021. This study investigated the outbreak in 2021 to determine the scope, and the factors associated with transmission.

A probable case was defined as a resident of Semuto Subcounty with acute onset of fever and a generalized maculopapular rash with either cough/cold or red eyes from 1 June to 31 August 2021. A confirmed case was defined as a probable case with a blood sample positive for measles-specific IgM. A village-matched case-control study was conducted with 30 cases and 122 controls (1:4 ratio). A control was defined as an individual aged 6 months-9 years, sampled at random, with no signs or symptoms of measles from 1 June to 31 August 2021, residing in the same village as the matched case. Adjusted Mantel-Haenszel odds ratios (OR_MH) and confidence intervals (CIs) were calculated.

Of the 30 cases (27 probable and three confirmed), 16 (53%) were male. The subcounty attack rate (AR) was 3.2/1000. Children aged 5-9 years were the most affected (AR 5.0/1000). Twenty-two (79%) cases and 116 (97%) controls had ever received measles vaccine (OR_MH 0.13, 95% CI 0.03-0.52). Interaction with symptomatic persons at water collection points (OR_MH 4.4, 95% CI 1.6-12) and playing at community playgrounds (OR_MH 4.2, 95% CI 1.7-11) increased the odds of infection.

Socializing/congregating at water collection points and community playgrounds facilitated the transmission of measles in this outbreak.