In 2017, 75 measles cases were reported as a result of an outbreak that began in Hennepin County involving the Somali community. This was the largest measles outbreak experienced since 1990, and the second major measles outbreak to affect the Minnesota Somali community in 6 years. Sixty-six cases were residents of Hennepin County, and the remaining were residents of Ramsey (3), Crow Wing (4) and LeSueur (2) counties. Of the 75 cases, 68 (91%) were laboratory confirmed, and 7 (9%) were epidemiologically-linked to laboratory confirmed cases. Of those with lab testing done, 68 were positive by PCR and 68 were genotyped; of 68 genotyped, 63 (93%) were B3. The remaining 5 (7%) failed to be successfully genotyped.
The first 2 identified cases were confirmed on April 11 by the PHL. At the time the cases were reported, the outbreak was into its second generation with 9 infectious cases, and a third generation of 20 cases had already been exposed. The sibling of the second case had experienced a transient rash illness 2 weeks earlier, and was confirmed as the earliest case in the outbreak, with rash onset on March 30. This case had no international or domestic travel nor contact with any ill individuals. Though the source for the outbreak remains unknown, the genotype (B3) identified in the majority of cases is one that circulates year-round in many parts of the world including Sub-Saharan Africa. The outbreak continued through early July and was declared over on August 25 after two incubation periods had passed with no new cases.
Measles was transmitted in child care (n=32), household (n=26), school (4), health care (2), community (10), and unknown (1) settings. The median age for all cases was 2 years (range 3 months to 57 years). Sixty-one (81%) cases were of Somali descent; 1 (1%) was black and of non-Somali descent; 2 (3%) were white, Hispanic; and 11 (15%) were white, non-Hispanic.
Of the 75 cases, 68 (91%) were unvaccinated, of those 68, 5 (7%) were too young for vaccine and 63 (93%) were of age but unvaccinated. In addition, 2 (3%) had 1 previous dose of MMR vaccine, 3 (4%) had 2 previous doses of MMR, and 2 (3%) adults with unknown status stated they were vaccinated but no documented doses could be located. Twenty-one (28%) cases were hospitalized (mean 5.5 days; range 2-18 days). This outbreak was not unexpected, given the highly infectious nature of measles paired with the Somali community’s steadily decreasing MMR vaccination rates in young children. At the time the outbreak began, the MMR rate for 24 month-old Somali children born in Minnesota was at 42%; and 36% in Hennepin County. Though MDH and local public health partners have done outreach work with this community since before the 2011 outbreak, the fear of autism, and the targeted activism of anti-vaccination groups to spread misinformation about MMR vaccine continue to undermine public health efforts.
This outbreak also underscores the importance of early recognition, reporting and testing of individuals with febrile rash illnesses, regardless of travel history. With the exception of 2011 and 2017, 1 to 2 cases are reported annually, with 96% due to import-associated cases. Typically, cases are reported soon after symptoms develop, allowing MDH and local public health agencies to take rapid action to prevent a larger outbreak. However, in 2011 and 2017, the first case in each outbreak was misdiagnosed and unreported to MDH, allowing transmission to occur without appropriate response measures.
- For up to date information see>> Measles
- Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2017