Number of pertussis cases spiking in several states

Outbreaks of the bacterial disease have increased significantly, and theories abound as to why.

By Victoria Stagg Elliott — Posted Oct. 18, 2004

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Pertussis has increased dramatically in the past year, with several states reporting large outbreaks.

Nearly 10,000 cases had been reported to the Centers for Disease Control and Prevention by the end of September, a significant increase over the nearly 6,000 reported by this time last year. Much of this increase is accounted for by outbreaks in Midwestern, New England and the Mid-Atlantic states.

For example, Wisconsin had a total of 215 cases last year, but already has tallied more than 1,200 this year -- eight times what would normally be expected.

"There are a lot of cases occurring," said Jeffrey Davis, MD, state epidemiologist at the Wisconsin Dept. of Health and Family Services. "And it has had an impact on the public health system as well as the primary care physicians taking care of patients."

North Dakota also has seen a spike, with more than 600 cases this year compared with only six in 2003, although that outbreak now appears to be dwindling. "It's slowed down a little bit, and we're hoping we're seeing the end of it," said Heather Weaver, immunization program manager at the North Dakota Dept. of Health.

Casting blame

Most believe that much of the increase can be blamed on the vaccine's long-acknowledged waning effectiveness. Most children receive their last pertussis shot by age 6, and thus lose much of the protection it provides within a decade.

"We have a population that has waning immunity," said Dr. Davis. "And in the United States, there are no means to boost it."

But public health experts also believe that while the numbers are truly increasing, there are additional factors driving them. Many states have been utilizing improved testing technology that enables more accurate detection of a higher number of cases. Some states also have improved public health communications systems that have led to an increased awareness among many physicians.

"We had a lot of testing, and the more we test, the more you're going to find," said Weaver.

Public health departments are calling on physicians to report suspect cases and treat those patients and their contacts with antibiotics.

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Reasons for resurgence

  • The pertussis vaccine loses its effectiveness over time.
  • Population-wide or "herd" immunity among adolescents and adults is now at an all-time low because of successful efforts to vaccinate children. The vaccine's protection wanes faster than immunity that results from actually having the illness.
  • Improved testing techniques enable the detection of more cases.
  • Stepped-up public health communication programs have raised physicians' index of suspicion.

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External links

Pertussis information from the North Dakota Dept. of Health (link)

Pertussis information from the Wisconsin Dept. of Health & Family Services (link)

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