In 2000, the CDC declared that measles no longer was spreading in the U.S. Since then, there have been an average of 63 cases a year that come from infections acquired outside the U.S.
But as of July of this year, there have already been 131 U.S. measles cases. The number of imported cases hasn't gone up, but the disease is spreading much more readily. Four-fifths of the cases came in seven measles outbreaks.
Who's spreading the disease? It's largely children who don't get vaccinated because their parents hold "philosophical or religious beliefs" against vaccination, the CDC says.
"Even with our current extremely high vaccination rates, we could have significant pockets of people in outbreaks. And if vaccine coverage levels fall, we risk many more outbreaks. We are concerned," Jane Seward, MB, MPH, deputy director of the CDC's viral disease division, said at a news conference.
2 Outbreaks, 2 Pockets of Unvaccinated Kids
This year's two biggest measles outbreaks came in Washington State and in Illinois.
In Washington, an unvaccinated child likely caught measles at a church conference attended by 3,000 junior high school students, some from foreign nations. That child infected seven other children in her household; they spread measles to 11 other people. Of the 19 cases, 16 were school-age children. Eleven of these kids were homeschooled; none was vaccinated because of their parents' beliefs.
In Illinois, a teenager who recently returned from Italy -- where there are ongoing measles outbreaks -- seems to have infected four unvaccinated girls ages 10 to 14. Eventually, 30 people came down with measles. All but one of the cases were children or teens aged 8 months to 17 years. Cases included 25 homeschooled children whose parents held anti-vaccination beliefs.
Seward says that as of 2006, an estimated 93% of U.S. kids had been vaccinated against measles. New numbers are expected soon. But because these estimates rely on data from previous years, the CDC can't yet tell whether vaccination rates are dropping.
That would be worrisome, because it will take 95% vaccine coverage to keep measles from re-establishing itself in the U.S. In the U.K.. fears that the measles vaccine might be linked to autism dropped vaccination coverage there to 80% to 85% of the population.
Very high coverage rates are necessary because measles is one of the most contagious diseases known to man. If a person with measles coughs in a room of 100 unvaccinated people, Seward says, 90 to 95 of those people will get the measles.
And many of these people would get very ill. Uncomplicated measles is a serious illness, but some kids who get the illness come down with life-threatening encephalitis or pneumonia . In the years before vaccination became common, a few children each year developed a very rare measles complication called subacute sclerotic panencephalitis -- a degenerative brain disease that is almost always fatal but which can take up to 10 years to kill.
"Encephalitis complicates one to three in every 1,000 measles cases, and you can never tell which child will be the unlucky one that has a severe complication," Seward says. "We have not seen measles encephalitis yet this year, but we could. And we have seen cases of pneumonia, which is another serious complication."
Most at risk are people who can't take the measles vaccine -- very young children and people suffering cancer or immune disorders.
Fortunately, none of the U.S. measles cases this year has been fatal, although 15 people were hospitalized -- including four babies under 15 months of age. But there were two deaths in Europe this year, one in Italy and one in the U.K.
"Both of these children were immuno-compromised and could not take the vaccine, but they would hve been protected if there were higher immunity in their community due to better vaccine coverage," Seward said.
States With Measles Outbreaks
The last time the U.S. had as many measles cases at this time of year was 1996.
Fifteen states have seen measles this year:
- Illinois (32 cases)
- New York (27 cases)
- Washington State (19 cases)
- Arizona (14 cases)
- California (14 cases)
- Wisconsin (7 cases)
- Hawaii (5 cases)
- Michigan (4 cases)
- Arkansas (2 cases)
- District of Columbia (1 case)
- Georgia (1 case)
- Louisiana (1 case)
- Missouri (1 case)
- New Mexico (1 case)
- Pennsylvania (1 case)
- Virginia (1 case)
Measles vaccination is recommended for all healthy children, with one dose at age 12 to 15 months and a second dose at the time of school entry. However, vaccination as early as age 6 months is advised for U.S. children traveling abroad or during community outbreaks.
The CDC's updated measles report appears in the Aug. 22 issue of Morbidity and Mortality Weekly Report.
By Daniel DeNoon
Reviewed by Louise Chang
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