Officials at Charlottetown's Queen Elizabeth Hospital are having a hard time identifying a gastro-intestinal illness that has closed Unit 3 to visitors.

More test results are expected back Friday, says hospital CEO Rick Adams.More test results are expected back Friday, says hospital CEO Rick Adams. (CBC)

Several patients have become ill, and a new case was reported on Thursday.

"We believe it's certainly a virus. But the virus seems to have alluded us in some way, shape or form, in that it comes and goes before we have the opportunity to really identify what it is," said hospital CEO Rick Adams.

"We test for certain viruses - that would include norovirus, norwalk, rota virus - but the tests have come back negative."

Adams said food poisoning has been ruled out. Two more test results are due back Friday.