Legionella control in the tropics

Legionella pneumophila, the main cause of legionnaires’ disease, multiply primarily in aqueous environments at temperatures between 30 and 45°C. Under these conditions, in certain water systems with aerosolization, L. pneumophila can grow in the system and be dispersed into the surroundings. Humans exposed to the aerosols can become infected and in some cases contract legionellosis (legionella pneumonia), which is a dangerous and sometimes fatal disease. The legionella problem is characterised by outbreaks in which many people simultaneously are infected and become ill, and community-acquired legionellosis in which a single individual is infected and becomes ill. These outbreaks and community-acquired legionellosis have led in the Netherlands (and several other mostly Western countries) to regulations for drinking water, process water and cooling-water systems. These are founded on the conduct of risk analyses and the establishment of a control plan.

Although it is known that a portion of the Western patients become infected abroad (30% in the case of the Netherlands), little is known about the occurrence of the disease in the tropical countries themselves. This is possibly the result of the absence of specific regulations and a lower awareness level on the part of physicians.


Legionella risks associated with water systems in the Netherlands can, for the most part, be qualified on the basis of water temperature and the probability of the growth of L. pneumophila, which is the most dangerous species compared to non-pneumophila species. Because the temperatures in water systems in the tropics are more frequently ideal for the growth of L. pneumophila, it can be expected that the multiplication of L. pneumophila in drinking-water and cooling-water systems will occur more often in these areas. The characterisation of L. pneumophila isolates from patients and from the aqueous environment shows that not all of the environmental isolates are found in the patients. The higher risk of multiplication of L. pneumophila in the tropics therefore requires, more so than in the Dutch context, the quantification of only the pathogenic sequence types of L. pneumophila in the environment, thus preventing any alarm about the multiplication of L. pneumophila strains that seem to play no role in the disease.

The thermal control concept, which underlies legionella prevention in the Netherlands, is founded on the principle: ‘keep the cold water cold’ (below 25°C). However, the concept does not apply in the tropics, since the drinking water temperature there is naturally above 25°C. These relatively high temperatures in cold water systems mean that innovative techniques are required to find solutions for legionella prevention in such systems.


The partners in this research want to establish which pathogenic L. pneumophila sequence types are found in legionellosis patients in Indonesia, or in foreign legionellosis patients who have visited Indonesia. This information will then be used to develop a quantitative PCR method, so that these specific sequence types in environmental samples can be quantified.

The project will also involve on-site testing in Indonesia of three different techniques to prevent the growth of biofilm and/or L. pneumophila: copper/silver ionisation, chlorine dioxide (prepared on-site), and a technique that limits phosphate availability for biofilm growth.


In July 2018 a seminar was organised for stakeholders in Jakarta. On the occasion, the project partners presented the project and called directly on the managers of collective water distribution installations or water-cooling systems to participate in a pilot. The seminar was attended by about 80 people, representing, among others, government, industry and a number of hotels. However, the response to the call to participate in a pilot was very limited, essentially because the legionella problem is not (yet) a high priority in Indonesia. The current status, in March 2019, is that a pilot location has not yet been found.

In the meantime, at the WLN laboratory in Manado (Sulawesi), legionella pneumophila strains have been received for closer characterisation using MLST (multilocus sequence typing). In addition to the ISO culture method, the WLN laboratory in Indonesia is also making use of IDEXX’s Legiolert. Most strains are identified by the application of this analytical technique on environmental samples (hotel drinking-water installations and cooling-water systems). In the summer of 2019, we will have a picture of which Lp sequence types are present in Indonesia, and will make a decision on the development of a quantitative PCR method.