More than 500 package-holidaymakers are poised to bring one of the largest mass travel claims after severe stomach upsets broke out at a Spanish hotel for the second time in two years.

Health inspectors ordered the hotel, Club Aguamar in the Spanish resort of Calas de Mallorca, to close its swimming pools after seven guests were diagnosed with the stomach bug crytosporidium.

The travel pressure group Holiday Travelwatch said it had been contacted by almost 50 of the hotel's guests and believed ten times as many could be affected in some way.

It is helping some of the guests to prepare claims against the tour operator JMC, part of Thomas Cook.

The Club Aguamar was at the centre of a food poisoning epidemic – this time involving salmonella – in 1998, which resulted in 650 guests falling ill and 100 being hospitalised. The hotel was operated by Sunworld, now known as JMC.

Andrew Bowden, customer services director at Travel Protection Group, said: “Food poisoning claims generally have been fairly stable and large outbreaks are a fairly isolated occurrence.”

Bowden said tour operators had forced hotels to tighten their hygiene standards because of the 1992 European Package Travel regulations.

These rules make tour operators directly liable for package-holiday claims which originate abroad, allowing claims to be pursued more easily.