*Rate per 100,000 population based on the U.S. Census Bureau’s population data as of July 1, 2003
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. 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.
There were 34 cases of legionellosis reported in Indiana in 2003, for a rate of 0.6 cases per 100,000 population (Table 1). Figure 1 shows the number of reported cases of legionellosis for 1999-2003. The number of reported cases increased during the summer 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 70-79 years (3.2) (Figure 3).
Legionellosis occurred throughout Indiana in 2003; however, only Marion County had five or more reported cases with an incidence rate of 1.2 cases per 100,000 population. No outbreaks of legionellosis were detected in Indiana in 2003.
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