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Whooping Cough returns with a vengeance

Before Christmas, Lynn Morales thought that her daughter's "barking seal" cough was croup. Three or four weeks later, when the cough was worse and constant, the Minneapolis mom took the four-year-old to the pediatrician, who suspected whooping cough. Morales was stunned. She'd had her daughter vaccinated on schedule, and the girl doesn't go to day care, a haven for communicable disease. Plus, whooping cough hasn't been a major public health concern for 50 years. But a test confirmed the diagnosis, and three months later, the preschooler still has coughing fits at night. It's possible the cough could linger for another three months.

The Bordetella pertussis bacteria, which causes whooping cough, is spread like the common cold. The bacteria attach to the fingerlike projections, or cilia, in the respiratory tract and release a toxin that paralyzes the cilia. The respiratory tract becomes inflamed and the cilia can't help clear the mucus. Complications can include breathing problems, brain disorders, and pneumonia.

For adults, whooping cough is a painful and time-consuming annoyance. It can mean missed days of work and, sometimes, a cough so violent it leads to vomiting. But for infected infants, the disease is life threatening, and it's one of the first things babies are vaccinated for.

Jane Sherman

Whooping cough reared its microbial head in 2004 like it hadn't since the 1950s, just after the introduction of the whooping cough vaccine. The number of cases last year was five times as high as the year before; there was one infant death in Minnesota due to the illness. Worse, the disease now also appears to strike some children, like Morales's daughter, who have had all of their shots, as well as middle-school-age children, who are no longer resistant. School nurses and pediatricians are on high alert.

Public health officials expect whooping cough resurgences every three to five years, says Kris Ehresmann, section chief for Immunization, TB, and International Health for the Minnesota Department of Health, but the number of cases in 2004 was "very high," illustrating the growing severity of peak years. Whooping cough cases in Minnesota soared to 1,024 in 2004, while in 2000, the last outbreak year of whooping cough, only 575 cases were reported. At this rate, 2008 could be frightening.

"It's like an escalating roller coaster," Ehresmann says. "Each peak has been higher than the previous peak."

 

The whooping cough comeback is not necessarily attributable to any one cause. Testing methods are more sophisticated, but there is a real spike, and public health officials will only theorize about the reasons. People continue to be more mobile, increasing their chances of exposure to whooping cough. Adolescents who were vaccinated as children now have more or less defenseless immune systems. People also just aren't exposed to whooping cough with the regularity they once were, so there is little natural immunity. And no vaccine offers 100 percent protection.

Overall immunization rates are up in Minnesota, but the number of parents who conscientiously object to immunizing their children is also up. (Mercury is in the whooping cough vaccine.) Immunization is certainly important for protecting infants, the group that is most vulnerable to whooping cough. But because of the nature of the whooping cough vaccine, older children are susceptible and can act as a disease reservoir--think Typhoid Mary with braces--potentially infecting very young or unimmunized children.

And it's starting to show. For instance, Olmsted County, which includes Rochester, had seven cases of whooping cough in 2003. More than 95 cases had been identified at last count in 2004, says Larry Edmonson, director of Disease Prevention and Control for Olmsted County Public Health. The vast majority of those infected with whooping cough in Olmsted County, Edmonson said, are adolescents.

The whooping cough vaccine provides durable, or temporary, immunity. Children really only have about three years of full immunity after the final shot is administered. In 2002, a MDH study of Minnesota kindergarteners said that 82 percent had received the recommended vaccines. At about 90 percent vaccination rates, herd immunity is said to occur; that is, the vaccinated members of the group provide protection to all others, even if they're not vaccinated.

"We've had a wonderful success story with vaccine-preventable diseases, except for pertussis," Ehresmann says.

Last week, a Food and Drug Administration panel approved an adolescent whooping cough booster. This would protect teens from acquiring whooping cough, but this may merely be a temporary means of dealing with a public health concern. As children continue to get more and more vaccinations, teens and adults are no longer naturally equipped to deal with these diseases. This waning immunity could be dangerous in the long term.

Whooping cough also is on the rise nationwide. Estimates put the number of whooping cough cases close to 20,000, with Minnesota contributing about five percent of the cases. According to the Wisconsin Department of Health and Family Services, more than 5,000 cases of whooping cough were identified in Wisconsin in 2004, about 25 percent of the cases reported nationally. The North Dakota Department of Health reported 658 cases of whooping cough in 2004.

The Society for Adolescent Medicine says 40 percent of the 11,000 cases of whooping cough nationwide in 2003 were adolescents between the ages of 10 and 19. Children receive the DTaP (diphtheria, tetanus, pertussis) vaccine five times between two months and six years of age. Because the vaccine is only given to children under seven and immunity decreases three years after the final shot, by the time children reach 11 or so, the vaccine has all but worn off. The decreased immunity leaves them susceptible to infection.

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