RAIL union RMT says that it will consider balloting members for strike action over the threat of “potentially lethal” legionella found on Thameslink trains.

The union said today that there were seven toilets on four trains that had “actionable traces” of the bacteria, which can cause Legionnaires’ disease – a potentially fatal condition.

The rail operator, which claimed that there was “no recorded case of anyone ever contracting legionella from a train,” stressed it had drained and bleached the infected toilets.

But RMT slammed bosses for their “half-hearted and inadequate” response to the threat, and called for an urgent meeting of Thameslink’s joint safety committee.

Legionnaires’ disease — a lung infection caused by bacterial infection — can kill, but the condition is treatable if caught early with intravenous antibiotics and oxygen. Initial symptoms are flulike and include a cough, high fever and muscle pain.

Legionella bacteria are commonly found in sources of water, such as rivers and lakes, and sometimes find their way into man-made water supply systems.

RMT general secretary Mick Lynch said that the union had been “raising concerns for weeks now” amid a greater focus on infection-control measures during the Covid-19 pandemic. 

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.”

Thameslink train services director Rob Mullen confirmed a “very low level of legionella was found to be present during testing in a small number” of Thameslink class 700 train toilets.

“Legionella can potentially be spread through atomised water droplets in the air in enclosed spaces, but water in our toilets is gravity-fed, which makes this extremely unlikely and further lowers the already very low risk,” Mr Mullen claimed.

“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.”