Pollution
Humain
Environnement
Economique

An episode of grouped cases of legionellosis was identified on 7 November in the suburbs of Lisbon. The first case occurred on 14 October, and the number of infected patients peaked on 6 November.

The municipality identified and geo-referenced all installations equipped with wet cooling systems and all potential sources of aerosols. On 8 November, the disinfection of drinking water and water in swimming pools and fountains was reinforced. On 9 November, the authorities requested that all cooling towers in the region be stopped and disinfected.

Using epidemiological data, retro-calculation models were used to determine the aerosol diffusion period (exposure period) and the estimated total number of cases.

The epidemic was declared under control on 21 November. No more confirmed cases were reported after 24 November. A total of 375 confirmed cases, including 12 fatal and 50 severe cases, were reported. The light wind and high humidity in the air during late October and early November facilitated the spread of bacteria.

A comparison between the clinical and environmental strains pointed to an air cooling tower operated on a mineral and nitrogen fertilizer production site as the origin of the contamination. The first patient, who presented symptoms on 14 October, was in charge of the maintenance of cooling towers at this site. The cooling tower in question was last inspected in 2012 (three-year periodicity). In accordance with environmental legislation, 5 legionella analyses had been carried out by the operator since that date. The most recent one, conducted in May 2014, had given standard results.

The company was administratively closed on 11 December and reopened 1 month later, and then legal proceedings were initiated against the facility operator by the Ministry of the Environment.

In April 2015, more than 300 people filed a joint complaint and formed an association to obtain compensation.

This episode was the most important to date in Portugal, and one of the most important on a European and global scale (one of the 3 largest known in the world). However, its mortality rate (3.2%) was lower than the world average (15%). Mostly men between the ages of 50 and 60 years were affected.