Recent outbreaks of measles and whooping cough show how easily a rare or "eradicated" disease can flare up again, U.S. investigators said this week.
Three people in Indiana were hospitalized last year after a 17-year-old girl carried measles back from Romania. It spread to 34 people because many in her community had refused to be vaccinated, a team at the U.S. Centers for Disease Control and Prevention said.
Their report on the outbreak is carried in Thursday's issue of the New England Journal of Medicine.
Measles is a highly infectious virus that can cause rash, fever, diarrhea, pneumonia, brain inflammation and even death.
It was declared eliminated from the United States in 2000 and became rare in developed countries through use of the measles, mumps and rubella vaccine.
However, the childhood disease has staged a comeback as people question the safety of vaccines: The World Health Organization estimates that measles infects 30 million people annually and kills 454,000 of them, mainly children.
In its weekly report on death and disease, the CDC also described a 2004-05 outbreak of whooping cough among 345 unvaccinated Amish people.
The Amish usually do not refuse modern medical care, but the affected families cited a fear of vaccine side-effects, the CDC researchers said.
Also known as pertussis, whooping cough is a bacterial infection that has been made rarer by a vaccine that also immunizes patients from tetanus and diptheria.
Whooping cough still infected nearly 26,000 people in 2004 in the United States alone. It killed 13 children, mostly infants, in 2003.
Infection spread through church
In the Indiana measles case, the unvaccinated girl returned from Romania with the disease and went to a church gathering the next day, the researchers said.
She infected 16 people, who infected others until 34 people carried the virus, the largest U.S. outbreak since 1996. Three patients had to be hospitalized: A 45-year-old man and a 6-year-old girl received intravenous fluids, and a hospital worker was put on a ventilator for six days.
Almost all of those infected had previously refused the vaccine for fear of side-effects, the researchers said. Some groups say vaccines preserved with a mercury compound called thimerosal can cause autism and other disorders.
The U.S. Institute of Medicine says studies show no link with autism, but media reports and campaigns by the anti-thimerosal groups persist. The ingredient has been removed from all U.S. childhood vaccines except the flu vaccine.
The CDC also noted the need for doctors everywhere to keep an eye out for outbreaks of various diseases.
"Measles imported into the United States may be the first indication of outbreaks occurring elsewhere," they wrote.
"At the time of the index patient's travel, Romania had not reported a measles outbreak, but several months later, it reported more than 4,000 cases."