Britain is currently being hit by an ‘unprecedented’ outbreak of a diarrhoea-causing parasite.
Cases of cryptosporidium – which can survive in swimming pools for up to a week – are now three times higher than normal.
Health chiefs are still baffled about the source of the outbreak, which has spread to every corner of the country.
But early studies suggest the spike is linked to swimming, where the parasite can spread through pools as well as wild water sources.
Officials investigating the unusual cluster of cryptosporidium cases believe it could be linked to holidays abroad as dozens of sick Britons traveled to Spain and other Mediterranean countries.
There have been 2,411 cases of the stomach flu in Britain, with a peak of 450 weekly reports at the end of September, three times the number normally expected
In addition to diarrhea, cryptosporidium can also cause vomiting, stomach pain and fever.
The chlorine-resistant parasite is spread by infected feces that enter the mouth, for example by swimming.
Traces of dried feces can wash down an infected swimmer’s anus.
According to the U.S. Centers for Disease Control and Prevention (CDC), infected people can shed up to 100 million cryptosporidium germs in one bowel movement.
Swallowing just 10 is enough to make you sick.
A UK Health Security Agency (UKHSA) investigation into the outbreak found that the increase in August was seen due to an increase in the number of routine stool samples analyzing cryptosporidium infections.
Since then, 2,411 cases have been detected in the UK.
The number of weekly reports peaked at 450 at the end of September – three times as many as normally expected.
Officials suspect even these figures may be an underestimate of the true number of infected Britons, with many showing symptoms without seeking treatment.
Case numbers still have a long way to go before falling back to normal seasonal levels, meaning more Britons could report infections in the coming weeks.
Reporting the outbreak in the magazine Euro supervisionUKHSA experts wrote: ‘Given the scale and geographical spread of the exceedance across regions and countries of Britain, a single local exposure is an unlikely cause.’
A survey of nearly 500 patients, distributed by health officials to help pinpoint the cause of the outbreak, found that 54 percent of those infected had been abroad a fortnight before the first symptoms.
Of the 215 cases for which more detailed travel information was available, almost half reported traveling to mainland Spain or to islands such as Mallorca and Ibiza.
Two-thirds had gone swimming before experiencing telltale symptoms.
“Our initial findings suggest that swimming (in Britain or abroad), including the use of swimming pools, and overseas travel to various destinations may be behind the current increase,” they wrote.
But other potential sources of the “unprecedented and ongoing nationwide increase in cases” could not be ruled out, the team said.
“At this stage, other sources, for example contaminated food, cannot be excluded as contributing to the exceedance,” they wrote.
The experts added that they are working on a public health education campaign calling on the public not to use swimming pools while experiencing cryptosporidium symptoms, and also for 14 days after signs of illness have disappeared, because they can still infect others.
They also added that they are working with their EU equivalents, the European Center for Disease Prevention and Control, to help them with further investigation into the sources of the outbreak.
For most people, cryptosporidiosis – the technical name for the infection – is mild.
It usually goes away on its own, without any treatment, within a few days or weeks.
However, it can be more serious for vulnerable people, such as those with weakened immune systems and the elderly or patients undergoing cancer treatment.
Due to its highly contagious nature, people with symptoms such as diarrhea and/or vomiting are told not to stay at work or school until they have been free of these symptoms for at least 48 hours.