Long Island saw a significant rise in whooping cough cases in 2012, mirroring a national trend.
Suffolk County reported 515 cases in 2012, up from 314 in 2011. Nassau's cases more than doubled to 140 in 2012, up from 68 in 2011, a spokeswoman for the Nassau County Department of Health said Thursday.
The nation is suffering its worst year for whooping cough in nearly six decades, according to preliminary government figures.
Whooping cough ebbs and flows in multiyear cycles, and experts say 2012 appears to have reached a peak with 41,880 cases. Another factor: A vaccine used since the 1990s doesn't last as long as the old one.
The vaccine problem may continue to cause higher-than-normal case counts, said Dr. Tom Clark of the U.S. Centers for Disease Control and Prevention.
"I think the numbers are going to trend up," he said.
Despite the surge in illnesses, whooping cough deaths did not increase. Eighteen people died, including 15 infants younger than 1, records show.
Officials aren't sure why there weren't more deaths, but they suspect the attention paid to outbreaks across the nation resulted in infected children getting diagnosed and treated with antibiotics faster.
Also, a push last year to vaccinate pregnant women -- a measure designed to pass immunity to infants -- may have had some success, Clark said.
The final tally will be higher but unlikely to surpass the nearly 63,000 illnesses in 1955, he said.
Whooping cough is a highly contagious disease that can strike people of any age but is most dangerous to children. Its name comes from the sound children make as they gasp for breath.
For about 25 years, fewer than 5,000 cases were reported annually in the United States. But case counts started to climb again in the 1990s although not every year. Numbers jumped to more than 27,000 in 2010, the year California saw an especially bad epidemic.
Experts looking for an explanation have increasingly looked at a new vaccine introduced in the 1990s, and concluded its protection is not as long-lasting as was previously thought.
Children are routinely vaccinated with five doses beginning at 2 months, and a booster shot is recommended at around 11 or 12 years of age. Health officials are considering recommending another booster shot, strengthening the vaccine or devising a brand new one. With Patricia Kitchen