OxyFile #398

The epidemiology of Legionella pneumophila infections. 

Doebbeling BN; Wenzel RP 

Department of Medicine, University of Iowa Hospitals and Clinics, 
Iowa City. 

Semin Respir Infect, 2: 4, 1987 Dec, 206-21 


The study of outbreaks of Legionella pneumophila has been 
essential in understanding the organism, the disease, and its 
pathogenesis. Early epidemics defined the clinical spectrum: 
Pontiac fever is an acute, self-limited, febrile illness with an 
attack rate of 95% to 100% and an incubation period of 36 hours. 
In contrast, legionnaires' disease is a life-threatening 
bronchopneumonia with an attack rate of 2% to 7% and an incubation 
period of two to ten days. Three times as many males as females 
are affected with legionnaires' disease, and age, cigarette 
smoking, and chronic medical disease (particularly 
immunosuppression) appear to be separate risk factors. 
Furthermore, L pneumophila is responsible for approximately 1% to 
3% of community-acquired pneumonias, 13% of those acquired in the 
hospital and as many as 26% of atypical pneumonias. Diverse 
environmental reservoirs have been identified, including cooling 
systems, potable or domestic water systems, respiratory therapy 
devices, industrial coolants, and whirlpool spas. Hot water 
temperature, stagnant water, sediment, and the presence of other 
microorganisms are important factors in the amplification of the 
Legionellaceae. Although airborne transmission has been widely 
suggested, aspiration may be an important mode in certain 
patients. Regional and national surveillance may identify common 
sources and allow the introduction of early control measures. The 
latter have included primarily pulse and continuous 
hyperchlorination and super-heating hot water systems to 50 to 60 
degrees C. Experimental data suggest that ozone and UV light may 
be useful in the future. Additionally, cooling towers and 
evaporative condensers have been decontaminated and maintained 
with a variety of biocides. The prevention of outbreaks requires 
thoughtful planning, redesign, and good engineering practices.