Scientists from the Phuket Medical Science Centre found the bacteria in samples they took between January and December last year.

Director-general of the Department of Medical Sciences, Sukhum Karnchanapimai, said on Friday that the centre was assigned to periodically inspect establishments such as hotels, hospitals and shopping centres to ensure their rooms are free from Legionella bacteria and issue certificates to the establishments that reach required safety standards.

The centre checked water tanks, shower heads, taps, swimming pools, spas and parts of air conditioning units and collected 1,508 sample from hotels for testing.

They found the Legionella bacteria, which can cause pneumonia and other lung complications, in 116 samples or 7.69 per cent but the concentrations found were not enough to cause disease in people yet, Sukhum said.

Among the samples that tested positive for the bacteria, the three most suspect sources were shower heads at 13.2 per cent, spas at 12.9 and taps at 10.4. He said the authorities would continue to monitor the situation and urged business operators to regularly maintain and clean their water systems, toilet facilities and air-conditioners.

The bacteria is known to be potentially deadly through Legionnaires’ Disease, a severe form of pneumonia.

Milder cases of infection are termed as Pontiac fever, with flu-like symptoms that could become severe among over-45s, or people with chronic diseases such as diabetes and those who have low immunity.