The owner of a bacteria-infested spa has been fined after four teenagers suffered painful rashes and puss-filled pimples following a birthday pamper party in 2013.

Inspectors visiting the Kensington Salon and Spa in Swadlincote, UK, found harmful bacteria in some areas was 24,000 times the acceptable level.

The girls were diagnosed with folliculitis – an infection of hair follicles caused by bacteria (called pseudomonas aeruginosa) often related to spa pools. There were bacteria breeding around missing tiles and water tests had not been carried out in more than a year, it was found.

Owner Lisa Matthews admitted six charges of failing to ensure the safety of her customers and employees – having previously been served with a notice to address bacterial hazards. Derby Magistrates’ Court heard Matthews had been negligent and her duty of care to her employees and customers had fallen well below the expected standard. Matthews was fined £2,500 (US$3,768, €3,187) and told to pay a further £1,000 (US$1,507, €1,275) in costs and £120 (US$181, €153) to the victims.

Matt Holford, environmental health manager for South Derbyshire District Council, said it was “crucial” for spas to carry out water tests regularly, according to the BBC.

“A variety of infectious agents are associated with the recreational use of water and these can affect the skin, ears, eyes, gastrointestinal and respiratory tracts,” said Holford.