Health authorities are investigating the source of contamination at a popular island resort off the coast of Brisbane after more than 50 people fell ill within a matter of days.

The investigation was launched on Moreton Island’s Tangalooma Island Resort after dozens of reports of patients with gastro-enteritis filtered through to Queensland’s Public Health Unit from Wednesday.

Dr Kari Jarvinen from the Metro South Public Health Unit said initial tests of the drinking water at the site returned positive tests of a bacterial infection.

“This is being addressed and further testing is being undertaken,” he said.

“All guests and staff have been advised to boil their drinking water or use commercially supplied bottled water until the issue is resolved.

“Anyone on the resort or anyone who has recently visited the resort should be alert for symptoms of gastro-enteritis and seek medical advice if they have concerns.

“Initial reports to Queensland Health involved 50 cases, however the exact number of people potentially affected is unknown.”

A spokeswoman for Tangalooma Island Resort said the initial tests by authorities returned positive samples of E.coli (Escherichia) bacteria.

“Some of our guests and staff have reported illness consistent with nausea, vomiting, diarrhoea, stomach cramps and a general feeling of being unwell,” she said.

“We are currently working with both Queensland Health and Queensland Ambulance Service to ascertain exact numbers of guests and staff who have been affected and have also attempted to contact all guests who have departed the resort over this time.

“We can say for certain that over the past few days, less than 10 people have reported any health issues to resort management.

“There have been a number of cases we are aware of where guests have arrived to the resort recently with what appears to be viral infections consistent with Gastroenteritis, that was contracted prior to arrival.”

She said management had begun implementing its protocols to keep guests and staff safe.

“The resort has completed a chlorination treatment on the water supply and are awaiting results of this action,” she said.

“Advanced cleaning & sanitisation regimes are actioned in public areas and across guest facilities.

“All staff have been briefed of the issue and have been provided with relevant information to keep themselves safe and guests safe.

“All water is sourced from the underground water table and then filtered through the resort’s water-treatment plant.

“The quality and safety of our water-treatment facility and water supply is regularly audited by independent experts to meet all regulatory and safety requirements.

“To date there have been no previous issues of such a contamination in the resort’s long history.”

Notices and emails are being distributed within the resort, and surrounding properties are alerting visitors not to drink the tap water while bottled water is being distributed.

Queensland Health is preparing to send more investigators to the resort to continue testing.

-ABC