VANCOUVER -- Calling the novel coronavirus the "invisivirus" for the way it can be passed from person to person before the carrier has shown any symptoms, a medical health officer with Vancouver Coastal Health says "massive and deadly" outbreaks are not "inevitable" at long-term care homes.

In a in a Twitter thread published Saturday, Dr. Michael Schwandt said the health authority has developed a range of measures that could help other jurisdictions avoid large outbreaks of COVID-19 in long-term care homes.

Long-term care homes for seniors have proven especially vulnerable to novel coronavirus outbreaks, with nearly half of all COVID-19 deaths in Canada linked to care homes. Twenty-one care homes in B.C. are still in the midst of ongoing outbreaks

Some outbreaks have been particularly devastating: in Bobcaygeon, Ont., the Pinecrest Nursing Home lost over a third of its residents, while in Montreal, a police investigation is now underway after 31 residents died and others were found in extreme neglect at another home, Maison Herron.

Vancouver Coastal Health — which works in Vancouver, Richmond, the North Shore and the Sea to Sky region — has managed 17 of B.C.'s long-term care home outbreaks, Schwandt says.

In March, the health authority was dealing with two of the earliest and largest outbreaks, at Lynn Valley Care Centre in North Vancouver and Haro Park Centre in Vancouver. Schwandt said lessons learned from those outbreaks are the reason other outbreaks have been much smaller.

"No other outbreak since has come close in numbers, and several have been halted," he said.

The key, Schwandt said, has been the realization of just how easy it is for the virus to spread, often through short and fleeting contact. For instance, transmission has occurred through a care worker changing a resident's stockings, or staff eating in the same lunchroom.

That's why testing early and broadly — including those who have had even brief contact with infected people — and supporting workers to stay home even if they're not showing symptoms, or may be showing mild symptoms that don’t seem to fit with COVID-19, is so important, Schwandt said.

"Do not wait for contacts to become symptomatic; 'watchful waiting' is not your friend with the invisivirus," he wrote.

"We are now doing asymptomatic tests of entire floors/buildings/units, and the entire staff of a LTC when transmission is suspected. This has routinely identified cases who otherwise would have gone undetected."

Health care workers have also found that, especially for older people, a range of symptoms — including "diarrhea, fatigue, confusion, or 'they just didn't seem like themselves' have all led to positive tests and successful prevention of spread," Schwandt wrote.