2005 - Pertussis

Table 1. Pertussis Cases by Race and Sex, Indiana, 2005

  2005 2005-2005
Cases Rate* Cases
Total 394 6.28 1,162
   White 358 6.45 1,074
   Black 20 3.60 61
   Other 11 6.75 22
   Not Reported 5 - 5
   Male 181 5.86 528
   Female 213 6.69 634
   Not Reported 0 - 0
*Rate per 100,000 population based on the U.S. Census Bureau’s population data as of July 1, 2005

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 394 reported cases of pertussis in 2005, for a rate of 6.28 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 2005, disease incidence was greatest during the late fall and winter months (Figure 2). Females (6.69) had a higher incidence rate than males (5.86). The rate for other races (6.75) was higher than that for whites (6.45) and blacks (3.60).

Pertussis is the most frequently reported vaccine-preventable disease among children under age 5. In 2005, 34 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 (83.64). 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 54 percent of all reported cases in 2005.

Infants less than 1 year of age are also at greatest risk for severe disease as evidenced by the proportion of cases hospitalized. In 2005, 41 of the 72 cases (57%) in infants under
1 year of age were hospitalized.

The incidence rates were highest among the following counties reporting five or more cases: Clinton (38.1), Jefferson (37.0), and Knox (33.9). Fifty-eight counties reported at least one case during 2005. Figure 4 shows Indiana counties with five or more reported cases for 2005.

Laboratory confirmation was reported on 202 of 394 cases (51%) in 2005.

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.

Table 2: Vaccination History of Selected Age Groups and Number of Doses (percent), Indiana, 2005

Age Group Number of Cases Number (percent) Not Appropriately Immunized Unknown Vaccine History
7-11 Months 5 3 (60%) 0
1 Year 14 3 (21%) 0
2-4 Years 48 8 (17%) 4
5-9 Years 47 7 (15%) 5