*Rate per 100,000 population based on the U.S. Census Bureau’s
Pertussis (whooping cough) is an acute respiratory disease caused by the bacterium Bordetella pertussis. The illness is characterized by the onset of profuse nasal discharge, sneezing, low-grade fever, and a mild cough. The cough usually becomes more severe during the second week of illness as the patient experiences sudden uncontrollable attacks (paroxysms) of numerous, rapid coughs. During these attacks, the patient may appear blue due to lack of oxygen (cyanotic). Vomiting and exhaustion commonly follow such an episode. Following this paroxysmal phase, which may last 1-10 weeks, a convalescent stage occurs where the coughing spells become less severe and frequent. Transmission most commonly occurs by the respiratory route through contact with respiratory droplets or by contact with airborne droplets of respiratory secretions.
Indiana had 364 reported cases of pertussis in 2004, for a rate of 5.84 cases per 100,000 population (Table 1). Pertussis incidence, unlike other vaccine-preventable diseases, has increased since the 1980s. Figure 1 shows this increase since 1986 as well as the cyclical nature of pertussis. This increase in Indiana is similar to incidence trends observed throughout the United States and is generally believed to be attributable to better recognition and reporting of suspected cases. In 2004, disease incidence was greatest during the late summer and fall months (Figure 2). Females (6.15) had a higher incidence rate than males (5.51), and the white population (6.06) had a higher incidence rate than the state rate (Table 1).
Pertussis is the most frequently reported vaccine-preventable disease among children under age 5. In 2004, 35 percent of all cases occurred in children less than 5 years of age. Incidence rates were highest for infants less than 1 year of age (90.59). Figure 3 shows incidence rates for all age groups. Although the incidence rate for adolescents and adults was lower, persons aged 10 years and older accounted for 53 percent of all reported cases in 2004.
Infants less than 1 year of age are also at greatest risk for severe disease as evidenced by the proportion of cases hospitalized. In 2004, 37 of the 78 cases (47%) in infants under
1 year of age were hospitalized.
The incidence rates were highest among the following counties reporting five or more cases: St. Joseph (38.3), Jefferson (37.4), and Cass (27.2). Fifty-five counties reported at least one case during 2004. Figure 4 shows Indiana counties with five or more reported cases for 2004.
Laboratory confirmation was reported on 162 of 364 cases (45%) in 2004.
Unvaccinated children are at highest risk for severe disease, but fully or appropriately immunized children may also develop illness. Efficacy for the currently licensed acellular pertussis vaccines is estimated to be 71-84 percent for preventing disease. Table 2 shows the number and percent of cases that were not up-to-date for pertussis vaccination at time of illness for selected age groups.
|Age Group||Number of Cases||Number (percent) Not Appropriately Immunized||Unknown Vaccine History|
|7-11 Months||17||9 (53%)||1|
|1 Year||16||3 (19%)||3|
|2-4 Years||34||11 (32%)||2|
|5-9 Years||42||6 (14%)||6|