A mystery smell returned at Fanny Allen in Colchester this week, sickening staffers and forcing the cancellation of dozens of surgeries.

Our Cat Viglienzoni spoke with the UVM Medical Center's interim president on Monday. She didn't get many answers. Interim President Dr. Stephen Leffler told her it's a mystery.

He said the strange smell started in Operating Room 4 last Wednesday. Seven people went to urgent care with symptoms like nausea, lightheadedness and dizziness. Two had their blood tested and showed very low levels of carbon monoxide.

Tests of the air in the rooms, though, didn't come back with anything.

The hospital canceled or moved about 75-100 surgeries scheduled for this week so they can bring in investigators to try to figure out what's causing it.

Reporter Cat Viglienzoni: What does this smell smell like?

Dr. Stephen Leffler: Different people have said different things. Some people say it smells like exhaust from a car. One of the doctors just told me it smells a bit like a burnt hamburger. Some people say it smells like a dirty gas smell, like from the hood of a kitchen. Those are the kinds of smells they talk about.

This also happened back in October. Seventeen people got sick then. That time, the smell started in Operating Room 1 and then spread to the other rooms.

All of the rooms use the same air handler. We're told air in those areas cycles out 20 times an hour.

The hospital says in both of these cases, OSHA has been involved, as well as a private consultant.

Hazmat will be there Wednesday to do their own tests, too.

We heard from patients who are frustrated their surgeries have been put off. And the hospital doesn't yet know when they will reopen the OR. They've moved everything for this week.

Leffler said depending on what they do or don't find this week, they'll reassess later in the week to figure out whether they feel it's appropriate to bring patients and staff back into those areas. Otherwise, they will move more surgeries to the main campus or reschedule them for the near future.

Other services at Fanny Allen, like rehab and physical therapy, are going on as usual.