Legionella does not spread from person to person, but often occurs in stagnant, lukewarm water in, for example, shower heads or pipework. Showering with water contaminated with legionella can be dangerous. It can lead to a serious lung infection, especially in people with weakened immune systems, the elderly, or smokers. In less severe cases it can cause flu-like symptoms. Symptoms include fever, coughing, muscle aches and shortness of breath.