Michael Osterholm, PhD, MPH, director of the University of Minnesota's Center for Infectious Disease Research and Policy (CIDRAP), which publishes CIDRAP News, said the media and even some public health officials are missing key elements of the hantavirus outbreak on a Dutch cruise ship.
During a Q&A with CIDRAP News, he explained how and why superspreaders are key to understanding the Andes strain of hantavirus, why close proximity is only part of the consideration, and why he doesn’t think this outbreak is the next “big one.”
Per the World Health Organization, the outbreak that began on the MV Hondius cruise ship traveling from Argentina to Europe has resulted in 11 cases. Three patients have died since April 11.
Today, the US Centers for Disease Control and Prevention confirmed that no Americans have been sickened so far in this outbreak. The agency said it is monitoring 41 people for the virus, at least 18 of whom are being quarantined in biocontainment units.
Person-to-person transmission and superspreaders
CIDRAP News: What are the biggest misunderstandings you see in coverage of this outbreak?
Michael Osterholm: Unfortunately, the media and some of my colleagues have missed the main point of this outbreak.
First of all, respiratory person-to-person transmission is not new with the Andes hantavirus. We have an example from Chubut Province, Argentina, which was well-documented in a study in the New England Journal of Medicine. Thirty-four cases and 11 deaths in that outbreak.
We have had at least three other outbreaks in Argentina since 1996 that show person-to-person transmission. In 1996 there was an outbreak involving 16 people, in 2002 we saw an outbreak with 13 linked cases, and there were three linked cases in 2014.
We have had at least three other outbreaks in Argentina since 1996 that show person-to-person transmission.
CIDRAP News: So, is person-to-person transmission likely?
Michael Osterholm: There have been over 100 cases of hantavirus in Argentina this past year and no reports of person-to-person transmission. It’s a rare phenomenon, but it happens. Transmission likely involves superspreaders, individuals—for reasons not clear—who transmit at high rates via the respiratory route to other humans.
We have a model for that with SARS [severe acute respiratory syndrome] and MERS [Middle East respiratory syndrome], a handful of cases who really drove the activity in a given outbreak.
Another study in Morbidity and Mortality Weekly Report describes a woman who contracted hantavirus in Argentina, flew back to Delaware, and exposed 51 or 52 people. No one became infected.
These experiences give us more reason to believe what is happening on the ship will be self-limited. Many cases do not transmit the virus. From a standpoint of transmission, every person does not pose the same risk, and that point has been missed.
Right now, every person in quarantine from this outbreak is being treated like they are a superspreader who brought it on the ship. Our challenge is we won’t know who a superspreader is until after it happens. And we won’t know if there will be a superspreader for another two to three weeks.
Swapping air and asymptomatic spread
CIDRAP News: The cruise ship element is really driving this story and begging comparisons to COVID. What’s your take on the ship’s role in the outbreak?
Michael Osterholm: From an HVAC [heating, ventilation, and air condition] standpoint, a cold-water cruise ship is all about keeping the ship warm. It’s not a cruise ship in the Caribbean, where people are drinking martinis on the deck; this ship poses different issues.
Many of these ships have lots of air that gets moved around inside the actual ship. This is why we can have cases who were not exposed in close proximity, or close physical contact. It’s all about who is swapping air, and we are not talking about that. Investigators need to think about who swapped air with whom.
It’s all about who is swapping air, and we are not talking about that.
CIDRAP News: There’s been some talk about possible asymptomatic transmission in this outbreak; what’s your take?
Michael Osterholm: We don’t know; maybe it could happen in the first 24 hours before symptom onset. There have been 10 cases among more than 160 contacts, not counting Patient Zero. That attack rate is relatively low, around 6%. If I were going to try to devise a transmission event on a cruise ship for cold-weather sailing, I would expect 50% to 60%.
I express my condolences to everyone who died or was on the ship, but I believe the current outbreak is not a major transmission crisis at all. To my knowledge, no one has been infected from someone who got off the ship early.
Prediction: It will likely be over in 2 weeks
CIDRAP News: About those who left the ship early, why aren’t they quarantining for 42 days in biocontainment units like 16 Americans in Nebraska and two in Atlanta?
Michael Osterholm: The lack of consistent response is a huge challenge, because it lends itself to a credibility gap. One of the challenges here is no one has the exact science.
One signal that’s been missed… everybody is focused on 42 days, but the median incubation is 18 days. That means half the cases would be anticipated to occur in the first 18 days after exposure.
Half the cases would be anticipated to occur in the first 18 days after exposure.
We know the original infected patient got on the ship around 30 days ago, and, based on when he got on the ship and when he died, he would likely have been transmitting the virus in his first week on the ship. To me, it points out that there’s not going to be a lot of additional cases from ship exposure.
Now, consistent with the concept of a superspreader, you may see enhanced transmission with one person, but that’s not what every person infected will do. People jump to this conclusion because a cruise ship is involved, and the [COVID-19] pandemic had cruise ships involved, but there’s no evidence this will be a pandemic. I think we will see this fade away over 10 to 14 days.
