Legionnaires disease is potentially lethal. When the bacteria is swallowed in low concentration, it usually passes through the system without adverse effect, but in some cases, people can have flu-like symptoms, diarrhoea and vomiting. The bacteria become highly dangerous, in higher concentrations, when airborne, and causes pneumonia and a wide range of illnesses that may be fatal. In the UK thousands of people become infected leading to amputations in some cases. There are 240 different strains of the disease.