NEW YORK - Outbreaks of whooping cough in four states are a sign the sometimes-fatal disorder has made a comeback despite mandatory vaccinations for children of school age, public health officials said last week.

Whooping cough, or pertussis, is a highly infectious condition marked by an unstoppable urge to cough.

"Just as we have been reminded that tuberculosis is still with us, we are seeing the reemergence of pertussis, a bacterial respiratory infection," said Len Horovitz, a pulmonary specialist at Lenox Hill Hospital in Manhattan. "Children who have not been adequately vaccinated with the standard DPT vaccine are at risk, as are adults whose immunity to the bacterium may have faded over decades."

Even though the 8,051 cases diagnosed this year is lower than in 2006, many have occurred within the last several weeks in outbreaks in several states, including Pennsylvania, South Carolina, Wisconsin and Ohio. A Colorado baby coughed to death last month from an infection once considered a disease of a bygone era.

"It has made a comeback, but the recognition of the disease is better and our ability to diagnose and treat it is also better," said Thomas Clark, a medical epidemiologist at the Centers for Disease Control and Prevention.

He said the pertussis bacterium produces a toxin that accelerates the formation of thick mucus in the lungs, which in turn drives an uncontrollable urge to cough.

Long considered a childhood illness, whooping cough occurs annually in a substantial number of adolescents and adults whose immunity has waned. A relatively new vaccine called T/dap, against tetanus, diphtheria and pertussis, was designed for people ages 19 to 64.

Clark stressed that pertussis had not come into the United States from abroad, as has been the case with other vaccine-preventable diseases in recent years. A recent mumps outbreak in Maine, for example, probably originated in Canada, where 1,140 people have been diagnosed with it this year.

Mortality related to pertussis is still low. Antibiotics are effective in the treatment, and good old-fashioned supportive care helps speed recovery, Clark said.