Water at a theme park is being tested for harmful microorganisms after dozens of children got “severe diarrhoea and projectile vomiting”.
Parents have questioned the cleanliness of the water park at Twinlakes in Leicestershire, with some areas described as “absolutely disgusting”.
The park is shut while Public Health England investigates the outbreak.
Twinlakes said the closure was a “precautionary measure” but has not responded to claims about hygiene.
Bosses could face prosecution by the Health and Safety Executive if investigators determine the park was responsible for visitors becoming ill.
Public Health England has not said how many visitors became ill, but dozens of people have complained to media organisations and via the Twinlakes Facebook page.
One, Vicki Maylor, said her three children all became ill after visiting on a youth club trip.
“They attended on a trip on Wednesday and by Thursday evening and Friday morning they were all vomiting, along with 20 out of 23 on the same trip,” she said.
Medical microbiologist Dr Tom Makin, who advises organisations on preventing infection from water systems, said last week’s heatwave could have played a part.
The water park’s hygiene control measures could have been “overpowered” by the influx of visitors prompted by the hot weather.
“What you normally find in a situation where there is an outbreak is something has gone wrong somewhere,” said Dr Makin.
“The control measures are not satisfactory or somebody has forgotten to do something.”
How have visitors been affected?
Children have suffered from vomiting and diarrhoea, and some adults have also fallen ill.
One father said his four-year-old child was put on a drip in hospital after getting “severe gastroenteritis” less than 24 hours after their visit.
Kelly Quinn said her son and daughter, eight and 10, both had “severe diarrhoea and projectile vomiting” after visiting on Wednesday.
About 30 children from a school trip became ill with diarrhoea and vomiting after visiting on Wednesday.
What might have made visitors ill?
Dr Makin said people can get “quite a large number of infections associated with swimming pools, particularly if they are not managed properly”.
One of the most common causes of infections is a parasite called cryptosporidium, which cannot be killed with the levels of chlorine that can be safely used in a swimming pool.
It causes diarrhoea and has a very low “infective dose”, meaning you only need a few cells to catch an infection.
“People come in with an infection, they may not know they’ve got it at the time, they have a faecal accident in the pool, and the organism is discharged in very large numbers into the pool,” said Dr Makin.
“Then when you are swimming in the pool you ingest a tiny bit and get the diarrheal infection as a result.”
Norovirus, one of the most common causes of gastrointestinal infection, can also be transmitted if a swimming pool is poorly managed, he said.
How should pools be kept clean?
Chlorine is normally used as a disinfectant at swimming pools and water parks, Dr Makin said.
However, filtration is also needed in order to remove any microorganisms which are resistant to chlorine.
Water should be passed through filtration systems several times a day, Dr Makin said, and control measures need to be checked “many times each day” to make sure everything is working properly.
“Hopefully, the Leicestershire water park will have the records to show that they have done that,” he said.
“In a well-managed pool you shouldn’t see infections.”
What effect could the heatwave have had?
Dr Makin said people typically rush to swimming pools and water parks when the weather is hot, and this can overpower control measures.
“If lots of people go in there chlorine can be neutralised, not just by microorganisms but by the various fats and oils that come off our bodies and skin cells, so there’s less chlorine available to do the job of killing off the bacteria and viruses that get into the water,” he said
“You find these places do get overused at this time of year and the control measures are overwhelmed by that.
“If you are ever going to see an outbreak associated with a swimming pool it’s normally about now.
“You’ve got to manage the number of people that go into a pool, and restrict them.”
Were there any warning signs?
Kellie Carr complained to Twinlakes last year after seeing algae in the water, describing it as “green and foul smelling”.
“I could smell the water as we were approaching from around the corner,” she said.
“As the algae was settled in the concrete floor this was slimy and causing a slip hazard also.”
She complained because it was a “massive health risk” to her son, who has cystic fibrosis.
However, Dr Makin said the algae could also indicate wider problems at the water park.
“If there’s green algae in there the control measures are not working properly, because you should never see that in a swimming pool,” he said.
“That’s an indication that maybe they haven’t got it right and it’s not been right for a while.”
What has Twinlakes said?
In a statement on its website, Twinlakes apologised for “any inconvenience or disappointment” caused by the closure of the water park.
“As soon as we heard reports that some visitors have become ill following their visit to the water park we took the decision to close it as a precautionary measure,” it said.
“We are working closely with the Health and Safety Executive to investigate and hope to be able to provide information about the re-opening of the Au Guang Dragon Water Park very soon.”
The rest of the theme park remains open.
Public Health England said it was working with the Health and Safety Executive, Melton Borough Council and park bosses “to investigate the reports and ensure that any necessary public health actions are taken”.