Notes from the Field: Measles Outbreak of Unknown Source - Shelby County, Tennessee, April-May 2016.

On April 15, 2016, local public health officials in Shelby County, Tennessee, were notified of a positive measles immunoglobulin M (IgM) test for a male aged 18 months (patient A). On April 18, 2016, a second positive measles IgM test was reported for a man aged 50 years (patient B). Both patients had rash onset on April 9, 2016. The Shelby County Health Department initiated an investigation, and confirmatory testing for measles virus on oropharyngeal swabs by polymerase chain reaction (PCR) at CDC was positive for both patients. On April 21, 2016, public health officials were notified of a third suspected measles case in a female aged 7 months (patient C) who had developed a rash on April 14; PCR testing was positive. Genotyping conducted at CDC identified genotype B3 measles virus in all three cases. Genotype B3 is known to be circulating globally and has previously been associated with imported cases in the United States (1).