Rapid testing solution for Legionella

Around 300-400 cases of Legionnaires’ disease are reported every year in England and Wales. While the incidence is low in hospitals, those affected will be the most susceptible – the immuno-compromised, ICU patients, transplant and oncology patients, diabetics, smokers and alcoholics – and the most likely to die. While the mortality rate for the general population is around 13%, the nosocomial rate has reached 32%. Legionnaires’ disease is the severest form of infection caused by Legionella bacteria, opportunistic waterborne pathogens which occur naturally in the environment. Of the 50 plus species, only 20 appear to be associated with disease in humans, with L. pneumophila being the most significant. Victims are infected by inhaling organisms suspended in air from an aerosol, or sometimes by aspiration, particularly by hospital patients. Although less than 5% of exposed individuals will go on to develop Legionnaires’ disease, up to 95% may contract a milder form of legionellosis known as Pontiac Fever, a short flu-like illness that does not require treatment. However, some exposed individuals will remain completely symptomless. Dormant at low temperatures, Legionella multiplies to large numbers in water at temperatures between 20°C and 45°C and cannot survive at temperatures above 50°C. Other risk factors for outbreaks are water stagnation, for example in pipework “dead legs”, leading to build-up of biofilm, which harbours pathogenic bacteria, and lack of appropriate biocide concentrations. Although 27% of Legionnaires’ disease outbreaks are associated with cooling towers, hot and cold water systems are also major culprits, with spa pools being the third most significant source. In new buildings, warmer weather and energy conservation requirements are also making cold water systems more vulnerable to microbial contamination. Heat is now better retained in buildings and is transferred to the cooler parts of the building, normally the cold water system. Even well insulated pipes may be inappropriately “warmed” by hot pipes running alongside cold pipes in service ducts or above ceiling mounted radiant heat panels. In the UK, there is a legal requirement to follow the “L8” guidelines1 to prevent Legionnaires’ disease. This includes sampling for Legionella species to monitor the effectiveness of control measures against the organism.

Traditional measurements

The traditional way of measuring Legionella quantitatively in water is based on a complex culture method which involves concentrating bacteria from water by filtration and/or centrifugation, followed by heat and acid treatments and culture on selective media including nutrients and antibiotics such as Vancomycin and Cycloheximide. Although currently the “gold standard”, the culture method can take up to 14 days to produce results. It also has an inconsistent recovery rate for bacterial cells, from between 20% to 70%, in turn giving variable results. However, a much faster solution is now available. In the last few years, very rapid real-time monitoring of Legionella in water systems has become possible with the development of quantitive polymerase chain reaction (qPCR), which can produce results within a matter of hours. This has proved a specific and sensitive method, yet so far cannot be adopted alongside culture as a method for compliance testing for Legionella counts because the action levels detailed in legislation and guidance such as L8 have been based solely on the standard culture method. Until now there has been no consensus on how qPCR results might be interpreted in relation to results from culture. But this could be about to change. Positive results from a multicentre European study to define, alert and action guidelines for the use of a qPCR protocol for monitoring the control of legionellas, and an evaluation trial in the UK at the Brighton and Sussex University Hospitals NHS Trust’s Environmental Microbiology Unit, have recently made steps forward in resolving this problem.