The outbreak accounted for more than half of the 66 measles cases in the U.S. last year, nearly doubling 2004's total of 37 cases — the lowest in nearly 90 years of record-keeping.
The girl unknowingly brought the viral disease back to her home state of Indiana, leading to 33 other people being infected — 32 from Indiana and one from Illinois, said the federal Centers for Disease Control and Prevention.
The outbreak caused no deaths, but three people were hospitalized, including a health-care worker who recovered after being treated in an intensive-care unit, the CDC said.
Only two of the 34 people in the outbreak had been vaccinated against measles.
"The outbreak occurred because measles was imported into a population of children whose parents had chosen not to vaccinate their children because of safety concerns, despite evidence that measles-containing vaccine is safe and effective," the CDC said in its weekly journal.
However, a "major epidemic" was averted because the community surrounding the outbreak area had high vaccination rates, the agency noted.
The girl became infected after visiting a Romanian orphanage while on a church mission trip, the CDC and state health officials said. The others became infected after they attended a church gathering with her the day after her return.
"Certainly orphanages are known to be higher risk" for measles, said Dr. Philip Gould of the CDC's division of viral diseases. "The main point is to ensure that people do get vaccinated, especially prior to leaving the country."
Nearly all of the 32 other U.S. cases in 2005 originated abroad, including 16 cases involving U.S. residents infected while traveling overseas and seven involving foreigners who were infected before visiting the United States.
In the decade before a measles vaccine became available in 1963, about 450,000 measles cases and about 450 measles deaths were recorded in the U.S. each year. The disease — often known by its characteristic rash that begins on the face and spreads — can cause ear infection, diarrhea or pneumonia. It kills about one in 1,000 patients, according to the CDC.
The U.S. vaccination rate against measles is now more than 90 percent.