BACKGROUND: In April 2015, Kamwenge District, western Uganda reported a measles 
outbreak. We investigated the outbreak to identify potential exposures that 
facilitated measles transmission, assess vaccine effectiveness (VE) and 
vaccination coverage (VC), and recommend prevention and control measures.
METHODS: For this investigation, a probable case was defined as onset of fever 
and generalized maculopapular rash, plus ≥1 of the following symptoms: Coryza, 
conjunctivitis, or cough. A confirmed case was defined as a probable case plus 
identification of measles-specific IgM in serum. For case-finding, we reviewed 
patients' medical records and conducted in-home patient examination. In a 
case-control study, we compared exposures of case-patients and controls matched 
by age and village of residence. For children aged 9 m-5y, we estimated VC using 
the percent of children among the controls who had been vaccinated against 
measles, and calculated VE using the formula, VE = 1 - ORM-H, where ORM-H was 
the Mantel-Haenszel odds ratio associated with having a measles vaccination 
history.
RESULTS: We identified 213 probable cases with onset between April and August, 
2015. Of 23 blood specimens collected, 78% were positive for measles-specific 
IgM. Measles attack rate was highest in the youngest age-group, 0-5y 
(13/10,000), and decreased as age increased. The epidemic curve indicated 
sustained propagation in the community. Of the 50 case-patients and 200 
controls, 42% of case-patients and 12% of controls visited health centers during 
their likely exposure period (ORM-H = 6.1; 95% CI = 2.7-14). Among children aged 
9 m-5y, VE was estimated at 70% (95% CI: 24-88%), and VC at 75% (95% CI: 
67-83%). Excessive crowding was observed at all health centers; no patient 
triage-system existed.
CONCLUSIONS: The spread of measles during this outbreak was facilitated by 
patient mixing at crowded health centers, suboptimal VE and inadequate VC. We 
recommended emergency immunization campaign targeting children <5y in the 
affected sub-counties, as well as triaging and isolation of febrile or rash 
patients visiting health centers.