"We have been fortunate so far and have not had the very high numbers seen in other parts of the state," said Dr. Carolyn Fruthaler, director of the Grayson County Health Department. "However, with winter on the way, and people spending more time in close quarters, we expect to see more."

Whooping cough cases have been increasing in Texas according to the Texas Department of Health since 2000 when 327 confirmed cases were reported over 45 counties throughout Texas, more than doubling the number reported the previous year. In 2001, 615 cases of whooping cough were reported in 70 Texas counties and this has been the largest number since the 802 cases reported in 1968.

In lightly populated Burnet County, with 86 cases in a population of only 40,000, health officials have been battling a continuing outbreak of whooping cough that began in May. The Central Texas county, which includes the cities of Marble Falls and Burnet, had no cases reported last year according to the Texas Department of Health.

This year between January and July, the Texas Department of Health reports a total of 378 cases of whooping cough recorded over 41 Texas counties, including four infant deaths. The report also states 30 percent of all patients have been children under one-year-old.

Immunizations will wane with age leaving teens and adults susceptible to the disease, Fruthaler said.

"An adult who has a cough for two weeks or more should be evaluated by a physician," she said. "We have had normal amounts of (whooping cough) vaccine and have not had to postpone doses; children should be up to date on that vaccine."

Dr. Sharilyn Stanley, TDH associate commissioner for disease control and prevention said a lot of youth don't cover their mouths and noses when they cough or sneeze, increasing the risk of transmission in school.

"Older children, teen-agers and adults usually have a milder case of whooping cough, but that is more likely to cause pneumonia, seizures, brain damage and death in infants," Stanley said. "The elderly and persons with weakened immune systems also are more likely to have severe complications. Any infant with a cough or difficulty breathing should be seen by a physician."

The first dose should be given at six weeks to two months of age, with subsequent doses at four months, six months and 15-to-18 months, and the booster dose at four years. Protection increases after each dose. The vaccine is not authorized for people seven and older.

Stanley said TDH is advising physicians to consider giving antibiotics immediately to patients with whooping cough symptoms and to their family members, instead of waiting for results of lab tests to confirm the illness.

Noting that the vaccine's effectiveness may diminish after a few years, Stanley added that physicians should not rule out whooping cough as a possible diagnosis simply because the patient has been vaccinated.

There are three stages of whooping cough. The first is marked by a runny nose, sneezing, low-grade fever and a mild cough and usually lasts for one to two weeks.

The second stage, typically lasting from one-to-six weeks, includes prolonged spasms of rapid coughs usually accompanied by high-pitched whoops as the person gasps for air. Vomiting often follows the coughing bouts.

In the third stage, coughing spells occur less frequently as the patient recovers over a two-to-three week span, but coughing spasms can recur for several months.

"It's usually not until the second stage, with the trademark coughing spells and whooping, that diagnosis and treatment occur," she said. "But someone with whooping cough can infect others throughout their illness."

The incubation period, or time from exposure to the appearance of symptoms, is typically seven-to-10 days but can range from four-to-21 days and longer.

People who have had whooping cough are not likely to have it again.

Many infants are not receiving immunizations at all. Texas ranks 50th in the nation in the percentage of children 19-to-35 months of age completing the recommended doses of several vaccines, including the one for pertussis, according to Texas Medicine, the official news magazine of the Texas Medical Association providing timely information on medical issues that affect Texas patients and their physicians.

Another possible cause is a reformulation of the vaccine, which may have reduced its strength. Pharmaceutical companies began manufacturing a partial cell vaccine, rather than one made from whole pertussis cells, in 1991. That year pertussis cases began to spike higher, though they had trended upward for more than a decade.