Here's how COVID-19 outbreaks inside Hamilton's Juravinski Hospital started and grew

A top health official at Hamilton Health Sciences (HHS) has broken down how COVID-19 spread inside Juravinski Hospital and caused five outbreaks in December.

Dr. Dominik Mertz, HHS medical director of infection prevention and control, presented the analysis during a Thursday town hall meeting.

The five outbreaks included the E3, B3, F5, E4 and M2 units, which range from a clinical teaching unit to one providing alternate level of care for people awaiting long-term placements.

City spokesperson James Berry says the outbreaks ranged between Dec. 3 and Jan. 12, with 106 infections and nine deaths.

The presentation at the HHS town hall shows some of what happened between Dec. 3, 2020 and Dec. 22, 2020.

Mertz said there were four strains of COVID-19 among the 33 cases the hospital network sampled, but only one of those strains, B.1.369, spread in the outbreaks.

None of the strains were the variants of concern that are accounting for roughly half of Hamilton's daily new infections now.

Breaking down the outbreaks

Mertz said the B3 unit outbreak had three cases between Dec. 3 and Dec. 4.

He also said it was most likely linked to the E3 unit through a health-care worker, though in an interview on Tuesday, Mertz said there's no way of knowing for sure.

He said in the E3 outbreak, after the virus entered the unit, patients got infected and then it spread to other staff between Dec. 3 and Dec 22.

"You can see how it walked through our ward," he said.

The third outbreak was declared on Dec. 4 in the E4 ward.

It was also the first of the outbreaks to see a new strain of the virus, though Mertz said that strain wasn't really linked to the other cases.

The outbreak had seven cases between Dec. 10 and Dec. 17.

Then two other outbreaks occurred.

The F5 ward outbreak was also declared on Dec. 4, but the first case was a new strain that didn't spread.

Then on Dec. 6, two people got infected with the main strain and a third person got another variant (though it also didn't spread).

A week later, four others got the main strain. And that infected three others over the next seven days.

The M2 ward had three cases, one of which was a strain that didn't spread.

The other two cases were linked, with one person getting the virus on Dec. 19 and the other getting it on Dec. 20.

Mertz said on Tuesday those outbreaks were most likely linked by patients.

"The typical transfers we have from a medicine or surgery unit to F5, which was back then, our alternative level of care setting ... that's why we had people transferred to those units before we knew we had an outbreak," he said.

"Because they were incubating at that point and developed the infection in the unit, we did see some limited spread."

What are the takeaways of this?

Mertz said this reinforces what experts said about the outbreaks.

"We did see spread and we had one particular strain that was responsible for the vast majority of those cases," he said.

Mertz added the cases weren't caused by long-distance airborne spread, with most cases occurring in rooms with multiple beds.

"It's that pattern of one here, one over there, one over there ... which wouldn't be what you would expect with a classical airborne pathogen like measles," he said on Tuesday.

In the town hall, he added there wasn't any one person, piece of shared equipment or service leading to dozens of infections.

He also said it wasn't a failure of personal protective equipment.

Mertz said the best way to avoid the spread would be to avoid moving beds or staff between units.