Legionnaires disease has a 25% mortality rate (Medscape)
Human and animal.
Transmission / Exposure Route
Infection normally occurs after inhaling an aerosol (fine airborne particles) containing Legionella bacteria. 
Anywhere from 8,000 to 18,000 people are hospitalized each year in the U.S. with Legionnaires' disease. (EH&E) Between 1980 and 1998, 35% of Legionnaires Disease cases met definition of nosocomial infection.
Disease is usually associated with man-made environments, such as cooling towers, whirlpools, and building water systems, where warm water (25C–42C) and biofilms support growth and survival of Legionella species. 
Case Fatality Ratio
Legionnaires disease has a 25% mortality rate. (Medscape)
Legionnaires' disease can be very serious and can cause death in up to 5% to 30% of cases. 
Between 1980 and 1998, the case fatality ratio decreased from 34% to 12% (P<0.001) for all cases, 46% to 14% (P<0.0001) for nosocomial cases, and 26% to 10% (p=0.05) for community-acquired cases. 
During an outbreak in the Netherlands the incubation period was reported to be 2-19 days (median 7 days, n=136), 16% of these individuals showed incubation times exceeding 10 days. 
Burden of Disease
U.S. legionellosis cases reported annually increased 217%, from 1,110 in 2000 to 3,522 in 2009, and the crude national incidence rate increased 192%, from 0.39 per 100,000 persons in 2000 to 1.15 in 2009. 
Between 1980 and 1998, the median annual number of cases was 360 cases/year. 
Elderly individuals, smokers, and people with underlying respiratory or immunocompromising conditions are at increased risk for Legionnaires disease. 
Figure 1. No. of cases of legionnaires disease (LD) and rate per 100,000 US residents, by age group, 1980–1998. (Surveillance data collected by the Center for Disease Control as presented in Benin, Andrea L, Robert F Benson, and Richard E Besser. “Trends in Legionnaires Disease, 1980–1998: Declining Mortality and New Patterns of Diagnosis.”)
Duration of infectiousness and disease
Symptoms include a high fever, chills, cough, muscle or headaches. These symptoms are common to most forms of pneumonia so diagnosis relies on chest X-rays and tests performed on sputum, blood, and urine. 
Excretion Rates (see Exposure)
A thin, aerobic, pleomorphic, flagellated, non-spore forming, Gram-negative bacterium of the genus Legionella. 
Legionella species are weakly gram-negative bacteria found primarily around fresh water environments, such as lakes and streams, where the bacteria use free-living amoeba as hosts for intracellular survival and multiplication.