Why Has Whooping Cough Returned?

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The current epidemic of whooping cough in California, reaching 6,631 cases for the year up to November 9, 2010, has many people wondering, why has whooping cough (pertussis) returned with such a vengeance?

Whooping cough cases are being analyzed

According to the Centers for Disease Control and Prevention (CDC), the number of new cases of whooping cough in the entire United States in 2007 was 10,454. When this number is compared with the 6,631 new cases in California, a number that continues to climb, questions arise.

The California Department of Public Health notes that the incidence of whooping cough (causative agent, Bordetella pertussis) has been rising steadily over the past 25 years, and it points to the declining number of people who have been getting routine vaccinations against this disease.

Of the ten deaths from whooping cough so far this year in California, all of them were babies who were two months or younger when symptoms began. Nine of them had not been vaccinated at all, and the tenth baby was a premature infant who had received his first DTaP (diptheria, tetanus, pertussis) dose at age two months, just 15 days before he developed symptoms. Given the immaturity of the immune system at such a young age, vaccinations cannot work properly.

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Whooping cough is a very contagious bacterial infection and one of the most common preventable childhood diseases. Before introduction of the vaccine in the 1940s, about 147,000 children in the United States developed whooping cough every year. By 1976 that number declined to a low point of 1,010, but it has been rising since that time.

Some people have asked whether Mexican immigrants in California are a cause of the whooping cough problem in that state. According to Ken August, a spokesman for the California Department of Public Health who was quoted in a recent LA Times article, “We absolutely do not think either legal or illegal immigration has anything to do with the California pertussis epidemic.”

August explained the reasons for this conclusion, including the fact that there is no outbreak of whooping cough in Mexico, immunization rates among Hispanic children are high, and Mexico was using a whole-cell vaccine which is likely more effective than the acellular vaccine used in the United States since the 1990s. He also noted that while Hispanic infants are overrepresented among whooping cough cases, overall the rates of the disease are highest among whites.

The CDC recommends the following vaccination schedule for whooping cough: six shots between birth and age 12, given at age 2, 4, and 6 months; between 15 and 18 months; between 4 and 6 years; and a booster at 12 or 12 years. A single dose of Tdap is recommended for adults ages 19 through 64.

Why has whooping cough returned? According to CDC statistics, it has been on the rise since its low point in 1976, and epidemics have begun to return over the last three decades. Infants who are not immunized or who have not completed the immunization process are especially susceptible to the disease, and adults who have not been properly vaccinated may contract the disease and pass it along to vulnerable children.

SOURCES:
California Department of Public Health
Centers for Disease Control and Prevention
LA Times September 16, 2010

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