Measles has been eradicated in the United States since 2000. Yet every year there are some measles cases that are linked to foreign travel.
The outbreak of cases in Minnesota is part of a larger surge in cases among young children nationally. Centers for Disease Control and Prevention is reminding parents and physicians that young children who travel or live abroad should get vaccinated for measles earlier than the usual schedule. That advice holds true even in foreign countries where measles is not typically considered a problem.
Still, this year's jump in cases among very young children is unusual.
Dr. Preeta Kutty, a medical epidemiologist at the CDC, said it's a sign that measles isn't on the minds of many travelers.
"That might be one reason why we're seeing increased cases, is that it's not on the radar here," she said.
Kutty thinks part of the problem could be outdated information about the hot spots for measles. In recent decades, most of the problem areas were associated with southern Asia, the Far East and Africa.
But the CDC's Dr. Gregory Armstrong said currently 39 percent of measles cases here originate in Europe.
"In the last 15 years or so, there's been a lot of cases in the United Kingdom, although their numbers are actually down relatively this year," Armstrong said. "There are more cases in Switzerland and France this year than we've seen previously. But there is measles in a number of European countries, including Spain."
Given the geographic spread of cases worldwide, the CDC suggests that parents who are traveling abroad with young children immunize them against measles as early as 6 months of age. That recommendation has been around at least since the 1990s. But Armstrong said many physicians and parents haven't gotten the message.
"I think clinics that specialize in travel are very up-to-date on these recommendations and understand them," he said. "But oftentimes parents will go to their regular pediatrician before they travel, rather than to a specialized clinic."
In fact, the CDC said that the parents of one of the children who got measles abroad this year reported that their pediatrician erroneously advised them that it was unnecessary to get the immunization before their journey.
Dr. Brett Hendel-Patterson has heard similar stories. He works at the HealthPartners Travel Clinic in St. Paul.
Hendel-Patterson says parents who come to his clinic are also encouraged to move up the booster shot schedule for their children, if they are taking them abroad.
"So that might mean that if a 3-year-old comes in to see me in the travel clinic, we would give their second dose then as opposed to waiting right before kindergarten, which is when more of the children wait to get that second dose of [the measles, mumps and rubella vaccine]."
The CDC highlighted Minnesota's measles outbreak in its Morbidity and Mortality Weekly Report published this week. The Minnesota summary provides more details on how measles cases spread so rapidly through the community.
According to the Minnesota Department of Health, a Somali child who contracted measles during a trip to Kenya was left at a drop-in child care center a day before that child developed a measles rash. Three children at the daycare then became infected in the days ahead.
Some of those children infected other kids at two living facilities for the homeless. There were also two infections traced to an hospital emergency room.
Epidemiologist Kris Ehresmann said measles is so contagious that even if the kids didn't cross paths directly, it's still possible to share the virus.
"There have been papers that were done kind of in the peak measles years looking at transmission where you had somebody who had measles, was seen in an exam room, 40 minutes later somebody comes into that exam room and that's their exposure and they develop measles. So it can hang in the air," Ehresmann said.
The Health Department is still receiving reports of possible additional measles cases. The current outbreak won't be technically over until three weeks have passed since the last case. The agency says that would be late April at the earliest.