There were more reported measles cases in the USA last year than in any of the previous 15 years, according to the Centers for Disease Control and Prevention (CDC). The majority of the 222 measles cases involved either visiting foreigners, or Americans who became infected abroad. In a typical year, there are from 50 to 60 reported cases. Fifteen years ago (1996), there were 508 reported cases.

The authors of the report added that low vaccination rates in various parts of the world, especially in Europe, contributed to a rise in reported measles cases in the USA.

Approximately one third of all measles cases had to be admitted to hospital. However, there were no deaths linked to the disease.

Over two-thirds of American citizens who became infected had not been vaccinated against measles.

By 2000, the USA had achieved measles elimination – interruption of year-round endemic measles transmission. The country’s progress in measles elimination has been hampered by infected people coming in from abroad.

There were 17 measles outbreaks in the USA in 2011. An outbreak involves at least three cases in any time or place. This compares to an average of 2 to a maximum of 10 each year since 2000.

Of the 222 reported measles cases in 2011:

  • 50% (112) were associated with 17 outbreaks
  • 90% were associated with importations from abroad
  • 52 cases involved American residents coming home from abroad
  • 20 cases involved non-US citizens visiting the country from abroad

measlescasesbystate
Origin of reported measles cases (N = 222) – United States, 2011

86% of all infected patients were either unvaccinated or had an unclear vaccination status. The authors emphasized the need to continue vaccination programs, in order to stem the spread of infection that comes in from overseas.

US health authorities consider cases to be imported ones if exposure to the measles virus took place outside the country from 7 to 21 days before the rash started, and rash occurred within 21 days of coming into the USA – plus, there was no known exposure to the virus in the United States during those 21 days.

Written by Christian Nordqvist