The number of confirmed cases of a waterborne disease caused by a microscopic parasite have more than doubled, while more than 100 further people have reported similar symptoms.

Around 16,000 households and businesses in the Brixham area of Devon have been told not to use their tap water for drinking without boiling and cooling it first.

The UK Health Security Agency (UKHSA) said on Friday that 46 cases of cryptosporidium had now been confirmed in the fishing town, up from 22 cases on Thursday, and that more cases were anticipated.

It added other reported cases of diarrhoea and vomiting in residents and visitors to Brixham were also under investigation.

Dr Bayad Nozad, consultant in health protection at UKHSA, said the Government agency was aware of further reports of illness above their confirmed numbers.

He said: “Please do not contact medical services to report cases unless you need urgent clinical care. If your symptoms last longer than seven days, or if you experience more severe symptoms such as blood in your poo, please contact your doctor who may recommend taking a sample for testing.

“Those with symptoms should stay off nursery, school and work for 48hrs since the last episode of illness and anyone with diarrhoea should not go swimming for 14 days after the last episode of illness.”

Typical symptoms can include watery diarrhoea, stomach pains, dehydration, weight loss and fever, and usually last for about two weeks but can be longer, Dr Nozad said.

News of further confirmed cases comes after a health expert said residents should “expect to see further cases for at least 10 days to two weeks”.

Paul Hunter, professor in medicine and infectious disease expert at the University of East Anglia (UEA), told BBC Breakfast on Friday: “So often in the past when I’ve been involved in investigating outbreaks, by the time you know you’ve got a problem, the problem has resolved itself anyway, but you can’t guarantee that.

“Yeah, even if they have stopped all new infections by now, you would expect to see further cases for at least 10 days to two weeks.”

Sally Dart, who runs homewares shop Flotsam 50 near Brixham Harbour, told the PA news agency business was “probably 30 to 40% down” and described South West Water (SWW) as “appalling”.

She said: “I would say it’s quiet and it shouldn’t be at this time of year.

“Quite a lot of us have symptoms from the virus – well, virus from the bacteria.

“We were all sitting around going ‘oh my God, why have I got a headache?’, but no-one was saying anything to us.”

Ms Dart said locals first felt symptoms after a busy pirate festival held in the fishing town between May 4 and 6.

On SWW, She added: “They knew they had this problem – obviously the reservoir couldn’t cope for some reason or another, it was getting all the stuff off the field into it.

“No one was checking the quality of the water and we’ve all got sick and it’s stupid, really.”

SWW issued a “boil water notice” for Alston and the Hillhead area of Brixham after water tests showed “small traces” of the parasite, which causes sickness and diarrhoea.

SWW chief customer officer Laura Flowerdew said on Thursday a damaged air pipe in a field containing cattle was a potential source.

Residents are being urged to boil water and let it cool before drinking it, preparing or cooking food or cleaning their teeth, though the company said water can continue to be used as normal for washing, bathing and flushing the toilet.

The disease can be picked up directly from the faeces of another person or animal, from swimming in or drinking contaminated water, or even by eating contaminated food such as unwashed vegetables.