Waterborne infection: reducing the risks

Infection with Pseudomonas aeruginosa has long been considered an inevitable endemic hazard for vulnerable patients on intensive and augmented care units, but the problem has now been catapulted into the limelight with the recent tragic deaths of four babies in neonatal units in Northern Ireland. As investigations into these events firmly established the source of infection as tap water, a flurry of new guidance – from the Regulation and Quality Improvement Authority in Northern Ireland1 and the Department of Health (DH) in England and Wales2 – has produced definitive guidelines that acknowledge the potential role of contaminated hospital water in the transmission of Pseudomonas to patients. The latest DH advice,2 published at the end of March, builds on previous guidelines from 2010, which were issued following earlier incidents in augmented care wards, where tap water was identified as the source of persistent colonisation with pseudomonad bacteria. The new guidelines emphasise water monitoring through regular sampling, risk assessment, water safety plans and best practice hand hygiene. If potential water contamination problems are detected, recommendations include use of an alcohol hand rub to supplement hand washing and use of sterile or filtered water, or water from a known bacteria-free source. Pointof- use (POU) filters are also recommended to provide bacteria- free water, with long-term use advised in some cases. The link between Pseudomonas infections and water is not new, however. According to Professor Matthias Trautmann, director of infection control of the Institut für Krankenhaushygiene (Institute of Hospital Hygiene) at the Klinikum Stuttgart in Germany, the connection between Pseudomonas and water was described as far back as 1993 in a children’s hospital in Freiburg in Germany.3 Speaking at a specialist master class on waterborne diseases held recently in Nottingham, Prof. Trautmann, who is well known in the field for his investigations into transmission of Pseudomonas, joined a panel of leading experts discussing not only the control of Pseudomonas, but other problematic waterborne pathogens such as Legionella, the cause of Legionnaires’ disease. The meeting was chaired by Dr Tim Boswell, consultant microbiologist at the Nottingham University Trust.

Pseudomonas epidemiology

The audience was introduced to Pseudomonas by Professor Kevin Kerr, director of infection prevention and control for Harrogate and District NHS Foundation Trust, assistant editor of the Journal of Hospital Infection and chair of the European Society for Clinical Microbiology and Infectious Diseases’ Study Group on Food and Waterborne Infection. He described how pseudomonad bacteria, including Stenotrophomonas maltophilia, can be found in most moist environmental niches in hospitals, including potable water from bottles, cold water dispensers and ice machines. These bacteria are very well adapted to live in damp conditions, he said, because of their ability to form ‘biofilm’, a sticky extracellular matrix which allows the organisms to attach to inanimate surfaces. They are also able to resist and even destroy the free-living aquatic amoebae that graze on other organisms. Pseudomonads do not present a problem to all patients; however, they can be lethal for immuno-compromised patients, of whom there are increasing numbers. In the UK, Pseudomonas is the cause of around 10% of nosocomial infections and is one of the most common causes of ventilator-associated pneumonia (VAP). As well as significant morbidity, mortality associated with infection in vulnerable patients can be high for those undergoing chemotherapy for solid organ and haematological malignancy, and in individuals with severe burns, for example. Onset of Pseudomonas infection in neutropenic patients can be very rapid and, unless treated promptly, can result in severe sepsis and other complications such as ecthyma gangrenosum. Pseudomonas is an increasing problem because rapidly rising antibiotic resistance to commonly used broad range antibiotics make infections increasingly difficult to treat. Resistance to ceftazidime, for example, is now as high as 50% in some places in Europe,4 while some strains of the bacterium are resistant to all antibiotics except one, colistin, used as a last resort because of its toxicity. Prof. Trautmann added to this, noting that Pseudomonas is an obligate aerobe, which needs air as well as moisture. This results in Legionella and Pseudomonas growing in different locations in water systems, he said. Legionella thrives in central water tanks and dead end pipes, resulting from modifications in older plumbing systems, where rather than destroying amoebae, it exploits them by using them as a host. However, Pseudomonas is mainly an endpoint problem as its need for air means it is more likely to grow in taps, mixing valves, tap aerators and rubber tubing. Outbreaks of Pseudomonas may result from contaminated humidifiers, bronchoscopes where filters have not been used for the final rinse, ventilators or even contaminated care products. However, in epidemics, Prof. Trautman said: “A large proportion of infections is due to transmission between patients. But many studies conclude that horizontal transmission has occurred if two patients have the same clone, yet the tap in the patient’s room hasn’t been checked, so some conclusions may be wrong. However, the mean of all the studies indicates around a 50% involvement.”