Measles, 2011

Twenty-six cases of measles were reported in 2011. This is the highest number of cases in Minnesota since 1991. A total of 6 cases were reported during the previous 5 years, including 3 unrelated cases in 2010. The most recent known transmission of measles within Minnesota occurred in 1991. Twenty-one of the 26 cases were associated with an outbreak in Hennepin County occurring in February through April, 3 cases were associated with an outbreak in Dakota County in August, and 2 unrelated cases occurred in Hennepin and LeSueur Counties during the time of the spring outbreak.

Of the 21 Hennepin County outbreak cases, 19 (90%) were laboratory confirmed; 11 (52%) were confirmed both by serology and PCR, 8 (42%) by PCR only. Genotyping was performed for 9 cases, including the index case, and was B3, a genotype circulating in Sub-Saharan Africa. All 3 Dakota County outbreak cases were laboratory confirmed; 1 by PCR only; the other 2 were confirmed by both PCR and IgM serology, and 1 of these was also culture-confirmed. The source case was genotype B3. The 2 unrelated cases were laboratory confirmed by both PCR and IgM serology.

The source case of the Hennepin County outbreak was a 30 month-old U.S.-born child of Somali descent who had traveled to Kenya. Measles was transmitted to 3 contacts at a drop-in childcare center (including the first identified case) and 1 household contact. Subsequent cases resulted in exposures in two homeless shelters (8), two health care facilities (3), two households (3), and another childcare center (1). One case’s specific exposure was unknown but was considered a community exposure. Fourteen (67%) cases were hospitalized (mean 4 days; range 2-7 days).

The median age of the Hennepin County outbreak cases was 12 months (range, 4 months to 51 years). Nine (43%) cases were black and of non- Somali descent, 8 (38%) were of Somali descent, 3 (14%) were American Indian, and 1(5%) was white.

None of these outbreak cases were known to have been age-appropriately vaccinated. Sixteen (76%) cases were known to be unvaccinated; of those, 7 (44%) were too young to have received measles vaccine in accordance with the routine schedule, and 9 (56%) were of age but unvaccinated. Of these 9 unvaccinated cases, 2 (22%) were behind on immunizations, and 7 (78%) were unvaccinated because of incorrectly perceived safety concerns, 6 (86%) of whom were children of Somali descent. Three (14%) of the outbreak cases had unknown vaccination history. One additional case, a health care worker with unknown vaccination status, had documented history of a positive measles IgG serologic test result. The remaining case was a child vaccinated at 11 months of age, younger than the recommended 12 months of age.

The source case of the Dakota County outbreak was a 12 month-old U.S.- born child of Ethiopian descent who had traveled to Kenya. Measles was transmitted to 2 other individuals; 1 was exposed in a private home and the other in a clinic setting. Two cases were hospitalized; 1 for 4 days and the other for 27 days. The critically ill case developed pneumonitis and required ventilator support for 15 days. The age range of the cases was 12 months to 43 years. Two cases were black and of Ethiopian descent and 1 case was white. The source case was too young to have received measles vaccine in accordance with the routine schedule, and missed the opportunity for early vaccination prior to international travel at 9 months of age. One case was not vaccinated because of incorrectly perceived safety concerns, and 1 case had unknown vaccination history.

The 2 additional unrelated cases occurred in white adults ages 27 and 34 years. These cases resulted from exposure in India and Florida, respectively. Genotypes were D8 (endemic to West Africa and India) and D4 (a genotype with many endemic locations), respectively. One had a documented history of 2 doses of measles vaccine; the other had unknown vaccination history. The cases were unrelated to the outbreak cases and to each other; no secondary cases were identified in Minnesota, although the Florida exposure resulted in 5 additional cases in two states.

• For up to date information see>> Measles
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2011