Investigations are being carried out in north Cornwall after an outbreak of a diarrhoea and vomiting bug.
About 200 people have had symptoms at holiday sites between Newquay and Padstow since the end of July, the Health Protection Agency (HPA) said.
The outbreak is suspected to have been caused by norovirus, the HPA said.
The local NHS, Cornwall Council and the Environment Agency are working to identify the source of the outbreak, the agency added.
Holiday accommodation outlets have been asked by the incident team to maintain a strict cleaning regime, especially for shared facilities, it said.
The HPA said: "It's not uncommon to see bugs like norovirus spread quickly through holiday settings like campsites and hostels, causing widespread diarrhoea and vomiting.
"We're working hard to see if we can find any source for the illness, which seems to be a bug which is passed from person to person."