The I:pidcniicilogy of Legionnaires' Disease 



Columbus, Dallas. Los Angeles, Memphis, New York, Norvvalk. and Pontiac, and from water and 

 soil from streams in Atlanta and Bloomington. Success in recovering the organism from environ- 

 mental sites does not implicate such sites in transmission of disease, but in some instances 

 epidemiologic evidence uiiplicating an environmental source has been supported by bacteriologic 

 results. 



More than 500 sporadic cases of LD have been reported to the Center for Disease Control 

 (CDC) from at least 43 states and the District of Columbia (Figure 1). Approximately \97o of the 

 reported cases were fatal, but this figure may overestimate the true proportion of fatal cases. The 

 distribution of reported cases indicates a 2.4:1 ratio of males to females, and 907r of reported 

 cases occur in people over 30 years of age. Cigarette smoking and alcohol abuse are clearly risk 

 factors in acquiring LD, and a significant minority of patients report recent travel or exposure to 

 excavation sites. Outbreaks and sporadic cases in the United States appear to be most common in 

 the summer. 



The Conference of State and Territorial Epidemiologists has collaborated with CDC in 

 establishing a reporting system for this disease in the United States. Outside the United States, 

 indigenous or imported cases of LD have been reported from Australia, Austria, Canada, Den- 

 mark, England, Israel, Italy, the Netherlands, Scotland, Spain, and Sweden. Cases have also been 

 associated with travel to other European countries. 



For some outbreaks and most sporadic cases, the mode of transmission of LD has not been 

 documented, but in several outbreaks there is strong evidence for airborne spread of the agent, 

 and it is possible that the airborne route is the only significant mode of transmission. Person-to- 

 person spread of LD has not been conclusively demonstrated and must occur rarely if at all. 



The need to isolate hospitalized patients with LD is not established, and superfluous iso- 

 lation of patients is detrimental to their care. On the other hand, the presence of the LDB has 

 been demonstrated in respiratory secretions from some infected persons; patients with LD may 



- 2.5 

 0.5-1.0 



n<.5 



CASES PER 1,000,000 POPULATION 



C2> 



PUERTO BICO 



^l 



O. 



VIRGIN ISLANDS 



FIGURE 1. Sporadic cases of Legionnaires' disease in the United States, May 1973 through October 1978. 

 Numbers within states indicate total reported cases per state. 



15 



