TUESDAY, Dec. 9, 2003 (HealthDayNews) -- Nearly 50 percent more babies developed whooping cough during the 1990s than in the 1980s, a new study says.
The study, in the Dec. 10 issue of the Journal of the American Medical Association, says the greatest increases were seen in children less than 4 months of age, especially those who didn't receive whooping cough vaccines on schedule.
"The best way to protect infants is to give them the vaccine on time," says study author, Dr. Masahiro Tanaka, a medical epidemiologist with the U.S. Centers for Disease Control and Prevention (CDC).
Whooping cough is another name for the disease pertussis. In its early stages, pertussis can easily be mistaken for the common cold. The first symptoms are a runny nose, low fever and a mild cough.
These symptoms generally last from one to two weeks, and then the second phase of the disease begins. This second stage can last from one to six weeks and is characterized by severe fits of rapid coughing. During these coughing spells, it's very difficult to breathe and the intense effort to inhale may cause the characteristic whooping sound.
After a vaccine became available for pertussis in the 1940s, the incidence of the disease dropped by about 99 percent, according to the CDC. Before the vaccine, there was an average of 200,000 cases per year in the United States. Since 1980, the U.S. averages an estimated 4,400 cases annually, the CDC reports.
The vaccine is usually given to infants at 2, 4 and 6 months of age. The vaccine isn't fully protective until sometime after the third dose, explains another author of the study, Kristine Bisgard, a medical epidemiologist with the CDC. Bisgard adds there is likely some immunity after the second dose.
For the study, the researchers used the CDC's National Notifiable Disease Surveillance System to gather information on the incidence of pertussis, mortality from the disease, and the vaccination status of those who contracted the disease.
Forty-nine percent more infants under 12 months of age developed pertussis in the 1990s compared to the 1980s. During the 1980s, there were about 12,550 cases of pertussis reported, compared to 19,798 during the 1990s.
Nearly 80 percent of the reported cases during the 1990s were in children less than 4 months old. Many of the children in this age group had already received at least one dose of vaccination, according to the study. Children who had received more doses of the vaccine were less likely to be hospitalized or die from the disease, the study says.
Dr. David Horwitz, a pediatrician at New York University Medical Center, says he's not surprised by the study's findings. He adds he has recently seen several cases of pertussis in teenagers in his own practice.
One of the reasons for the increase may simply be a natural increase in the disease, Horwitz says. "There's always been a natural cycle of three to five years where pertussis increases endemically," he says.
Parents can do a great deal to prevent the disease by making sure their children receive vaccinations on time, the researchers say.
Tanaka says many of the children who developed pertussis didn't receive a timely dose of their second vaccination. Also, parents should try to keep their kids away from anyone who is coughing. Bisgard says that advice is particularly true for parents of infants less than 2 months old because they are most at risk.
More information
To learn more about whooping cough, visit KidsHealth.org or the National Library of Medicine.
