Water Sector

DNA techniques help to detect legionella in the tropics

Conditions for the growth of legionella bacteria in water systems are different in the tropics than in the Netherlands. With drinking water temperatures above 25°C – the safe limit for the pathogenic Legionella pneumophila – the conditions in tropical countries are often ideal for the bacteria. A TKI project recently conducted by technology companies and research institutes in Indonesia has shown that L. pneumophila strains are extremely genetically diverse in Indonesian water systems and that these strains can actually cause disease.

Pathogenic bacteria

Legionella grows mainly in watery conditions at temperatures of 30 to 45°C. The bacteria can be spread through the air in some water systems where small water droplets (aerosols) are formed. That can expose people to a risk of legionnaire’s disease: an infection of the lungs that can sometimes prove fatal. In the Netherlands, legionella outbreaks have led to regulations for drinking water, process water and cooling water systems that require risk analyses and management plans to be drawn up.

Knowledge still scarce

Little is known about the number of cases of legionnaires’ disease in tropical countries. This may be due to a lack of regulation or to the priorities of doctors, who focus on other infectious diseases that result in high numbers of victims annually. It is therefore important to know the extent to which naturally occurring L. pneumophila poses a risk to public health.

Considerable variation

Water samples from different locations and sources in Indonesia have been analysed using cultivation techniques to isolate L. pneumophila strains. A total of thirty different L. pneumophila strains were found and they were then characterised genetically to produce a sequence type. The thirty strains belonged to 24 different sequence types, including ten types that have not previously been described or reported. Since most of the isolated strains are related to clinical strains, they are potential pathogens. The high genetic diversity of the L. pneumophila strains found and the fact that the sequence types of most L. pneumophila strains have also been found in patients mean that it is not useful to develop specific detection methods for the most common sequence types. It is better to monitor water systems in Indonesia generally for all L. pneumophila sequence types for which cultivation and qPCR methods are already available.