A growing problem

In July 1976, a then unknown disease disrupted an American Legion Convention in Philadelphia; causing 29 deaths and sickness in numerous members. Since then, scientific research has helped to elucidate the nature of Legionnaires’ disease - caused by species of Legionella bacteria (Figure 1).

Even with modern technological advancements, awareness of Legionella and legionellosis can still be significantly improved. In plenty of countries, the threat of Legionnaires’ disease is vastly underestimated. This is especially worrying in a world faced with the reality of increasing antimicrobial resistance.

Figure 1. 3D illustration of Legionella pneumophila, the causative agent of Legionnaires’ disease (Kateryna Kon, Shutterstock.com).


There has been an escalation in the number of reported cases in recent years. In Europe, between 2016 and 2017, there was a 30% increase in the number of cases in one year. Yet, only 4 countries represented approximately 50% of the number of reported cases in the EU/EEA population - France, Germany, Italy and Spain (Figure 2).

Surveillance and Distribution

Although Legionella is widespread in the natural environment, it is found in low numbers where it is outcompeted by other microorganisms. Instead, Legionella spp. are more prevalent in man-made environments such as cooling towers, fountains, air scrubbers, etc. Inside, Legionella bacteria thrive in temperatures between 20 °C to 45 °C and are provided the opportunity to gather nutrients from other microbes such as algae.

Figure 2. Distribution of Legionnaires’ disease cases per 100 000 population by country (EU/EEA, 2017).


European Guidelines and Legislation

In Europe, surveillance of Legionella is a joint effort between all EU member states, Iceland, Norway and Switzerland. The European Legionnaires’ disease Surveillance Network (ELDSNet) is tasked with the detection, control and prevention of outbreaks of legionellosis.

The introduction of the European Directive 2000/54/EC (18/09/2000) was instrumental in creating a culture in Legionella outbreak prevention. For the first time, employers had a duty to carry out risk assessments to protect their employees and site visitors.

Alongside the European Directive 2000/54/EC, a new edition of the “European Technical Guidelines for the Prevention, Control and Investigation of Infections Caused by Legionella species” (ESGLI, 2017) was released in 2017. These guidelines were drafted to advise authorities on risk assessments, preventative methods and on managing new sources of infection.

The UK possesses one of the first and most consistently enforced legislations for Legionella control and outbreak prevention in Europe. The L8 Approved Code of Practice (ACOP) exists to aid duty holders (e.g. employers) to comply with their legal responsibilities with regards to Legionella in the UK. ACOP L8 is supported by the Health & Safety Executive’s HSG274, “Legionnaires’ disease: Technical guidance” document which provides additional guidance covering the operation and management of evaporative cooling systems, hot and cold water systems, and other risk systems.

Spain also maintains strong Legionella regulations. The Royal Decree 865/2003 obligates parties to notify authorities regarding their cooling systems and they must possess readily available registers for health authorities.

In Germany, no regulations on registration and inspection of cooling towers even existed until 2017. In that year, an outbreak in the city of Bremen occurred, resulting in 3 fatalities. The investigation lasted 5 months as local authorities struggled to locate the source of infection due to the nonexistence of a cooling tower register. Strings of outbreaks since 2009 provided the impetus for the German Cabinet to pass the 42nd regulation, implementing the “Federal Pollution Act” in July 2017 (42.BlmSchV). Cooling tower registering became mandatory to prevent future Legionella outbreaks.

In Italy, decree No.81/2008 stipulates that companies who commit violations in occupational health and safety could be closed down. It has been mandatory to report cases of legionellosis to the Italian National Institute of Health (ISS) via Ministerial Decree 07/02/1983. The ISS subsequently issued the “Guidelines for the prevention and control of legionellosis” (Official Journal no. 103 of 05/05/2000) in 2000. It was updated in May 2015 to further assist parties in tackling Legionella in hotels, schools, hospitals etc. and to integrate previous knowledge into current international guidelines and scientific literature.

Hungary introduced legislation for controlling Legionella in November 2015 (49/2015.(XI.6.) EMMI rendelet), alongside technical guidance (3rd Edition, 2018) released by the National Public Health Institute (NPHI). Every cooling tower is now required to be registered with the relevant government authority.

Higher risk systems have been identified as open cooling systems and domestic hot water systems where individuals could exposed to water sprays. A risk assessment is necessary in public establishments e.g. hotel, spas etc. or if a company site contains an open cooling system. The guidance explains procedures for specific Legionella counts in hot water systems and open cooling systems.

A step towards progress

The most likely explanation for the increase in reported cases of Legionnaires’ disease is the improvement in detection methods and diagnoses. It is clear that Europe as a whole can still do a lot better to improve its health and safety protocols. An increasing number of European countries are now adopting more proactive policies and have begun to drift away from retrospective changes in legislation and guidelines. Water treatment companies have a key role in educating duty holders and driving the implementation of best practices to minimise the risks associated with Legionella.