The truth is that you quite probably aren’t sure. Few hospitals undertake routine monitoring of their water systems for Legionella pneumophila, and estimates of the number of hospital water systems infected range from 12 – 75%. Approximately 250 cases of Legionnaires' Disease are reported annually in the UK, of which around 4% are hospital-acquired. However, the true number of actual legionella infections has been estimated by clinical studies to be closer to 5000 per year, so there could be as many as 200 hospital-acquired cases of Legionnaires' Disease in the UK every year. In addition, while the overall mortality rate for all Legionnaires' Disease is around 10%, the rate for hospital-acquired cases is between 35 and 40% (up to 80 deaths a year). This is potentially a serious problem that hospitals have a legal responsibility to address