Although the bacteria responsible for Legionellosis has been ever present and therefore probably accounted for many unresolved cases of pneumonia. The first case where it was positively identified as the causative agent of infection was following an outbreak of illness at a convention of the American Legion, a military veterans organisation, in Philadelphia in July 1976.

221 cases were treated with 34 confirmed deaths from the infection. The infection was eventually traced to a cooling tower which served the air conditioning system of the Bellevue-Stratford hotel, the location where the convention was held.

Since this event outbreaks of Legionellosis have been regularly confirmed all over the world. Many cases have been linked with poorly maintained cooling towers such as Stafford Hospital (1988) 175 treated and 7 deaths, Burrow-in-Furness (2002) 180 treated and 7 deaths, Bulmer’s Brewery (2003) 20 treated and 2 deaths.

Possible sources of infection are still being identified with a recent HPA led report in the European Journal of Epidemiology linking vehicle windscreen washer bottles with Legionellosis. 20% of vehicles found to be without adequate levels of screenwash tested positive for the bacteria.

This led to an estimate that 20% of community acquired sporadic cases of Legionellosis (non-related cases) might be linked to this method of infection.