Most of the sick children's families "were not philosophically opposed to vaccination," Armstrong said. "They were unaware they could have been vaccinated at a younger age, or they had had an opportunity to get their child vaccinated but missed that opportunity for some reason. A lot of these children were a little bit delayed in their immunizations."
The latest cases "provided an opportunity to remind people that it's important to check the vaccination status of their kids before traveling," he said.
Before measles vaccines became available, hundreds of children died each year, thousands developed encephalitis and a quarter of them suffered permanent brain damage, he said. "People have forgotten just how severe measles is," he added.
The seven pediatric cases tallied in January and February alone roughly equaled the number of pediatric cases seen each year from 2001 to 2010. During that decade, CDC received reports of 159 imported cases, 47 of them among children younger than 2.
The children in the Morbidity and Mortality Weekly Report had traveled to at least six countries in Asia, Africa and the Caribbean. An investigation into a case picked up in the Dominican Republic strongly suggested transmission from a European tourist who had roomed next door to the family at an international resort.
Investigators probing the case of an infected child who had spent time in Haiti found no evidence the viral illness originated in that poor island nation, although a second U.S. resident who developed measles at about the same time was found to have been in the same international airport terminal, within the same two-hour period, as the sick child.
The highly contagious measles virus spreads through tiny droplets in the air, producing a telltale rash, and flu-like symptoms including high fever and a runny nose. Travelers can be exposed by breathing the same air as someone who is infected, such as in confined areas such as airports or airplanes, the CDC said. An estimated 1.9 million U.S. children travel overseas each year.
Armstrong and his co-authors wrote that U.S. doctors should "maintain a high level of suspicion for measles in patients with febrile rash illnesses and recent travel outside the United States" and advised them to report suspected cases to local health authorities and obtain specimens for testing and confirmation.
Of particular note to the authors was that in one of the 2011 cases, parents had asked their pediatrician about vaccination before traveling and were told it wasn't needed. Unfortunately, doctors may learn about measles in medical school, "but unless they work overseas, they're unlikely to see many cases of it, and it's frequently not recognized at first," Armstrong said.
Although the CDC report focused on cases among the youngest children, parents' decisions to delay or refuse vaccinations for their children have put older U.S. kids at risk when they venture abroad, said Dr. Terri Rock of Santa Monica, Calif., a family practice doctor who specializes in travel medicine.
"You can't imagine how many people we see for travel whose families don't vaccinate," Rock said.
When it comes time for their 17-year-old sons or daughters to go to developing countries for high school community service projects, they turn up in her office with lists of required immunizations for illnesses such as yellow fever and typhoid.