*Rate per 100,000 population based on the U.S. Census Bureau’s population data as of July 1, 2002
Legionellosis is a respiratory infection caused by Legionella bacteria, most commonly Legionella pneumophila. These bacteria are transmitted by inhalation of contaminated water aerosols. People over 50 years of age, especially those with a history of smoking and weakened immune system, are at the greatest risk of acquiring infection. For the five-year period 1998-2002, 71 percent of reported cases were aged 50 years or older. The severe form of legionellosis, commonly known as “Legionnaires’ Disease”, is characterized by pneumonia, fever, and myalgia. A milder, self-limiting form of the illness, known as Pontiac Fever, is characterized by fever, cough, and myalgia. Neither infection is transmissible person to person. Legionellosis can occur as individual sporadic cases or as an outbreak related to a point-source exposure. In 2002, cases occurred throughout the year with no seasonal patterns noted. No outbreaks of legionellosis were detected in Indiana in 2002.
There were 22 cases of legionellosis reported in Indiana in 2002, for a rate of 0.36 cases per 100,000 population (Table 1). The number of reported cases for 2002 was below the five-year (1998-2002) average of 43 cases per year. Figure 1 shows the number of reported cases of legionellosis from 1998-2002.
From 1998-2002, males with Legionella infections were reported 1.74 times more frequently than females. The incidence was greatest during the summer and fall months (Figure 2). The impact of Legionella infections was most notable when comparing cases by age group. The age group with the largest number of reported cases and the highest incidence rate was in persons aged 60-69 years (Figure 3). People aged 50 years and older accounted for 77 percent of all reported cases. For the five-year period, the black population had more than twice the incidence rate of the white population.
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