How long should Hantavirus cruise ship passengers self-isolate? And why does B.C. recommend less time than WHO?

Twenty-one days, 42, 45: Returning passengers from the hantavirus-hit MV Hondius cruise ship are facing different self-quarantining requirements, raising questions about how long is long enough to stay isolated from other humans.

The United States, United Kingdom, France and Greece have asked that all repatriated passengers from the vessel isolate for at least six weeks, or roughly 42 days — the quarantine period recommended by the World Health Organization.

Four Canadians who were aboard the infected cruise ship who arrived in British Columbia Sunday have begun a minimum 21-day isolation period, a stretch B.C.’s provincial health officer Dr. Bonnie Henry said might be extended as far as the full 42 days, depending on whether people develop symptoms and what’s happening globally.

“But as you can imagine, that’s quite a burden on people and it’s challenging to stay in one place for that period of time, especially as the risk diminishes over time,” Henry said, adding that the four passengers, none of whom were showing symptoms of infection Monday, are reasonable people who understand the risks. “I have no concerns that people are going to run off and go to a party or something.”

All four will be followed daily for the full 42 days of the risk period, in or out of self-isolation, Henry said.

An Ontario couple in the Grey Bruce region who were onboard the ship are being monitored for 45 days and isolating. A third person, a visitor to Canada who was exposed to a confirmed case of hantavirus on a flight, is also isolating in Ontario’s Peel region.

Tuesday, Spanish officials announced a Spanish man has tested positive while a French woman evacuated from the ship Sunday was in stable condition in intensive care. Given the long incubation of the virus more cases could be likely in the coming weeks, WHO officials have said.

Why are people facing different quarantine protocols and do people generally abide by rules for self-isolation? National Post spoke with Matthew Miller, who holds a Canada Research Chair in viral pandemics at McMaster University. The interview has been edited for clarity and length.

Why are some countries and jurisdictions taking what seems to be a more stringent approach to isolation?

There are a bunch of unknowns. This 42- to 45-day quarantine period is the most conservative in the sense that it’s meant to map onto the sort of maximum eight-week incubation period that we know hantaviruses can exhibit.

Given the relatively modest number of overall confirmed infections from the cruise ship (nine cases as of Tuesday, including three deaths, and two suspected cases) I don’t think we know with a high degree of precision yet exactly what the incubation period has been for this strain, or at least what’s been most typical.

The other thing that has not been reported very much publicly is a mapping of the relationships and contacts amongst passenger on board who did become ill.

Transmission of the Andes strain of hantavirus is not thought to be particularly efficient, in the way that we get very efficient airborne transmission of things like measles or COVID-19 or influenza. It’s really thought to require more sustained close contact.

And so that also has to layer onto risk assessment. Determining quarantine period is probably driven, at least to a certain extent, by whether the individuals who are not experiencing signs and symptoms had any degree of sustained or close contact with the people who did experience symptoms.

I think what’s reassuring by the statement put out by British Columbia is that they are saying a minimum of 21 days, which I think leaves the door open to extending that as more information becomes available.

I would expect that these individuals will be tested frequently to determine where or not their is an active infection happening.

But isn’t any kind of contact, on a relatively small ship, close contact?

If we’re talking about a virus like measles that is extraordinarily contagious in normal settings, one person might infect 12 to 15 other people. The data to date suggest the Andes virus requires sustained close contact, and not just close, like adjacent room. Close, physical contact.

There have (historically) been relatively few human cases of this virus and even fewer where the evidence has been for human-to-human transmission, rather than rodent-to-human transmission. There are a lot of questions about how efficient is airborne contact versus contact that actually requires direct exposure to bodily fluids or contaminated surfaces, for example.

Do we know what the reproductive number is for the Andes strain — how many people each infected person can go on to infect?

Based on previous outbreaks, it seems to be the case that, at a maximum, it’s one to two and, in many cases, it’s lower than one which is why these infections have fizzled out. As soon as the (reproductive number) sinks below one, an outbreak can’t sustain itself anymore.

What’s the distinction between quarantine and self-isolation?

In the most extreme forms of quarantine you might be in something like an isolation unit at a hospital or in some sort of health-care facility. Individuals would have to enter your room in personal protective equipment — gowns, masks. For nasty viruses like Ebola people might even wear suits that have dedicated air flow. That’s an extreme form of quarantine for viruses that are known to be both highly contagious and high virulent (meaning) of high consequence, likely to induce severe disease.

Self-isolation at home is obviously more appropriate for individuals who are at inherently lower risk and for pathogens that have inherently more limited ability to transmit.

What do we know about human behaviour in disease outbreaks? Do people abide by rules for self-isolation?

That’s a really good question. I don’t know, is the honest answer. But I think it also depends on the situation and perception of risk.

Early on in the COVID pandemic, there was a lot more adherence to isolation guidance than later, when people’s perception of risk changed based on their experience and a better understanding of who is at risk of getting severe infections.

I think, anecdotally, in situations where there is something particularly exotic and there are a lot more unknowns that adherence tends to be stronger than in situations where it’s a pathogen or a situation we might be more familiar with.

You mentioned that infections appear to be fizzling out, but it was reported Monday that a woman in France who was evacuated from the ship on Sunday tested positive for hantavirus and that her condition deteriorated quickly. What should we take from that?

It underscores that there are a lot of unanswered questions. This is not a virus that is super well studied and it’s not a virus that we have a huge degree of experience with, in terms of human infections and human transmission.

Questions about incubation period, exposures, what degree of exposure did this French woman have to other passengers who’ve had confirmed infections on the ship — all of those questions are big important questions.

We also don’t have a really strong understanding in humans about questions like, how long before a person experiences symptoms are they capable of transmitting? The sort of scant data that’s out there suggests that people don’t transmit very well, or very efficiently, until they become closer to being symptomatic (when people tend to have a lot of the virus in their system).

Overall, I would say that, given what a prime environment cruise ships are for transmission of pathogens, things like norovirus or diarrhea, we’re still talking about, thankfully, a very modest number of total passengers onboard this ship experiencing infection.

Does the Andes strain of hantavirus have pandemic potential?

After COVID I’m reluctant to ever exclude the possibility that something has pandemic potential. What I would say is this virus doesn’t seem to exhibit qualities that make it a high pandemic risk at this point

Efficient transmission is the critical parameter that defines pandemic potential. Efficient transmission doesn’t seem to be there.

If this was a dry run for another pandemic, how would you grade the response?

I think we are in some ways lucky that this isn’t a virus that’s highly transmissible. I think it underscores the need for more global coordination. Others have commented on the implications of the U.S. pulling out of the World Health Organization.

We’ve also seen jurisdictional complexities in this case: Where can the ship dock? How do we deal with the people onboard the ship? How do we evacuate them? What do we do when we evacuate them?

If it were a faster moving virus, it would be a lot more complicated. If this was a virus that transmitted quickly and made people really ill quickly, there would have been a lot more deaths and a lot more serious consequences.

National Post

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