Don’t panic, but take it seriously
A positive test is distressing information, but the good news is that you’re aware of this early on exactly because you implemented testing for Legionella (proactive testing is the most important thing you can do to protect the people around you).
The growth of legionella bacteria in a water system can lead to a risk of people contracting Legionnaires’ disease. This is a serious form of pneumonia that can have fatal consequences, as well as severe financial and legal repercussions for an organisation responsible for an outbreak.
Your immediate priorities following a positive test result for legionella bacteria on-site should be to Take action to protect the health and safety of the people in your care (staff, residents, visitors, etc);
Typically, any distal site positivity rate above 30% means that the people in your building could be at risk of contracting Legionnaire’s Disease. For example, if water from ten locations in your building is collected and tested, and more than three of those locations come back positive, that is considered a higher than 30% positivity rate.
Steps to take
The HSE’s Legionnaires’ disease Technical guidance Part 2 recommends that if the minority of results are returned with between 100 and 1000 colony-forming units per litre (CFU/l), the system should initially be resampled.
If it is still positive, then an assessment needs to be carried out to identify remedial actions, and a review of your control measures must be undertaken.
If the majority of the first sample results are between 100 and 1000 CFU/l, you will immediately need to review control measures and undertake a risk assessment to identify remedial action, including disinfecting the system.
If your sample has more than 1000 CFU/l, then you must resample the system and undertake an immediate review of control measures, as well as do a risk assessment to identify remedial action, including possible disinfection.
Retesting needs to take place a few days after disinfection and at frequent intervals subsequently until control is achieved.
If you are in charge of a facility with vulnerable patients, you will need to investigate and resample water showing detection of legionella under 100 CFU/l, with all the subsequent measures detailed above.