Legionnaires' disease people in and beyond the park. Legionnaires' disease Legionnaires' disease, also known as legionellosis, is a form of atypical pneumonia caused by any type of "Legionella" bacteria. Signs and symptoms include cough, shortness of breath, high fever, muscle pains, and headaches. Nausea, vomiting, and diarrhea may also occur. This often begins 2-10 days after exposure. The bacterium is found naturally in fresh water. It can contaminate hot water tanks, hot tubs, and cooling towers of large air conditioners. It is usually spread by breathing in mist that contains the bacteria. It can also occur when contaminated water is aspirated. It
Rare disease assumption odds ratio (OR) is equal to 16 and the relative risk (RR) is equal to 8.65. Although the prevalence in our example equals 10% it is very difficult to apply the rare disease assumption because OR and RR can hardly be considered to be approximately the same. However, in this example the disease is not particularly "rare"; a 10% prevalence value means 1 in 10 people would have it. As the prevalence drops lower and lower, OR approaches the RR much more closely. This is one of the most problematic aspects of the rare disease assumption, since there is no