Legionnaires disease is not that easy to define, but most of the doctors characterize it as a collective word for the health conditions provoked by legionella bacteria. They assign the severest forms of Legionnaires’ disease as well as several types of fever to this category. It is a life-threatening disease with most of the fatal cases. It can be called the last stage of pneumonia – a severe problem with lungs. Unfortunately, there are no guarantees, and all people are susceptible to infection.