Ontario’s ministry of health said it is now testing asymptomatic people with connections to a hantavirus-stricken cruise, a shift from government remarks made earlier this week, as health officials around the world grapple with the role of testing in the current effort to contain spread of the rodent-borne illness.
The province said the three "high-risk" travellers — two who were on the cruise and one who was on the same flight as a person who has since died of hantavirus — will stay in strict isolation regardless of their result.
However, a ministry spokesperson said the seven “low-risk” contacts can stop their recommended 45-day isolation if they test negative, while daily public health monitoring will continue.
“As an added precaution, testing has been offered to all identified contacts, even in the absence of symptoms, to further reduce any potential risk and to support early detection,” a spokesperson for Sylvia Jones, Ontario's health minister, said Friday.
Nine people in Canada have been classified as "high-risk contacts" and are isolating in Ontario, Alberta and British Columbia, while 26 others have been deemed "low risk."
Public health officials have described "low-risk" contacts as air passengers who were on the same flight as someone with hantavirus, but weren't in close proximity to them.
The question of whether to test asymptomatic people has been raised several times over the past week, complicated by the long incubation period of the virus, and potential for symptoms to show up weeks after exposure.
Earlier this week, Jones said the guidance from the province's top doctor was that it wasn't appropriate to test people showing no symptoms at the time.
Dr. Joss Reimer, Canada's chief public health officer, also suggested testing asymptomatic people might give a false sense of security.
“If somebody is perhaps testing negative, but later could go on to develop hantavirus, I don't want that individual to be taking their isolation requirements less seriously. So that's the balance that we're trying to strike in getting as much information as we can and is useful without giving people a false reassurance that might lead to unnecessary exposures,” Reimer said at a press briefing Friday.
Canada has two kinds of hantavirus tests: one that detects antibodies in the blood, and a PCR test, which finds particles of the virus itself.
The World Health Organization said its international hantavirus case count is 10, as the previous tally had an inconclusive test in the U.S. that’s since been confirmed as negative.
Three people have died. No additional deaths have been recorded since May 2.
More cases may be reported internationally in the coming days, since it can take up to six weeks to develop symptoms, said Dr. Maria Van Kerkhove, WHO's director of health emergency alert and response operations.
“This does not mean the outbreak is expanding. It shows that the control measures are working, that laboratory testing is ongoing, and that people are being cared for with support from their governments.”
On Friday, WHO held an emergency scientific consultation on Andes virus to discuss the latest research on transmission, diagnosis, treatment and vaccination.
Van Kerkhove said WHO is also working to better understand how this outbreak began and spread.
"The story of this outbreak, I think will be studied for years and years."
- With files from Nicole Ireland
This report by The Canadian Press was first published May 15, 2026.
