A rail union has said it will consider strike action over the threat of "potentially lethal" legionella found on Thameslink trains after trace amounts of the bacteria was found in seven toilets on four trains.
But what is legionella and what did the Rail, Maritime and Transport (RMT) union say?
Here’s what you need to know.
What is legionella?
According to the Centres for Disease Control and Prevention (CDC), legionella bacteria are naturally found in freshwater environments, such as lakes and streams.
The bacteria multiply where temperatures are between 20-45°C and nutrients are available, but are dormant below 20°C and do not survive above 60°C.
However, the bacteria can become a health concern when they grow and spread in human-made building water systems like shower heads and sink faucets, large, complex plumbing systems, and hot tubs.
After legionella grows and multiplies in a building water system, water containing the bacteria can spread in droplets small enough for people to breathe in.
According to the NHS, you can get Legionnaires’ disease if you breathe in tiny droplets of water containing bacteria that causes the infection.
Legionnaires’ disease is a lung infection you can get from inhaling droplets of water from things like air conditioning or hot tubs, and, although it’s uncommon, it can be very serious.
It’s usually caught in places like hotels, hospitals or offices where the bacteria have got into the water supply.
You can get Legionnaires’ disease from things like:
- air conditioning systems
- spa pools and hot tubs
- taps and showers that are not used often
You cannot usually get it from drinking water that contains the bacteria, other people with the infection, or places like ponds, lakes and rivers.
According to the Health and Safety Executive (HSE), testing of water quality may be carried out by a service provider, such as a water treatment company or consultant, or by the operator, provided they are trained to do so and are properly supervised. The type of test required will depend on the nature of the water of the system.
How often you should test water for legionella depends on the system that you have and the outcome of your risk assessment.
The HSE says that if you are an employer or a person in control of premises you must appoint someone to be responsible for helping you manage your health and safety duties.
If you decide to employ contractors to carry out your risk assessment for legionella - or other work - it is still the responsibility of the competent person to ensure that the work is carried out to the required standards, notes the HSE.
What are the symptoms of Legionnaires’ disease?
Symptoms of Legionnaires’ disease include:
- a cough
- difficulty breathing
- chest pain
- a high temperature
- flu-like symptoms
Why is the RMT considering strike action?
Thameslink said the toilets which contained traces of legionella had been drained and bleached, but the RMT union said this was "half-hearted and inadequate".
The union said there were seven toilets on four trains that had "actionable traces" of the bacteria which can cause Legionnaires’ disease, and has called for an urgent meeting of Thameslink’s Joint Safety Committee.
RMT general secretary Mick Lynch said the union had been "raising concerns for weeks now".
He said: "The latest cavalier approach from the company is pitifully inadequate and is an outright gamble with passenger and staff health.
"We have now declared a dispute. Be in no doubt, if we don’t get serious action we will ballot our members and do whatever is required to end this reckless approach to a potentially lethal situation on these increasingly busy trains."
However, Thameslink said there was "no recorded case of anyone, ever, contracting legionella from a train".
Rob Mullen, train services director at Thameslink, said: "A very low level of legionella was found to be present during testing in a small number of our Thameslink Class 700 train toilets.
"While it is extremely unlikely this would cause any harm to passengers or colleagues, the toilets affected were immediately locked out of use.
"The trains were taken out of service and these toilets have now been drained, bleached and had their tanks completely refilled."