Insights on the Hantavirus Outbreak

Michael Osterholm, a prominent expert from the University of Minnesota’s Center for Infectious Disease Research and Policy, has expressed concerns that key aspects of the hantavirus outbreak on a Dutch cruise ship aren’t being adequately covered by the media or public health officials.

In a discussion with CIDRAP News, he emphasized the significance of superspreaders in understanding the Andes strain of hantavirus, suggesting that close contact is just part of a larger picture. He also noted that he doesn’t see this incident as a potential major outbreak.

The outbreak, which started aboard the MV Hondius during its journey from Argentina to Europe, has resulted in 11 confirmed cases, with three fatalities reported since April 11, according to the World Health Organization.

Meanwhile, the U.S. Centers for Disease Control and Prevention has stated that there are currently no reported cases among Americans connected to this outbreak. However, they are monitoring 41 individuals, with at least 18 in quarantine within biocontainment units.

Understanding Transmission Dynamics

CIDRAP News: What are the biggest misunderstandings you see in coverage of this outbreak?

Michael Osterholm: It’s unfortunate that both the media and some colleagues have overlooked the core issues surrounding this outbreak.

Firstly, it’s important to note that respiratory transmission between people is not a new concept when it comes to the Andes hantavirus. For instance, there was a documented outbreak in Chubut Province, Argentina, which involved 34 cases and 11 deaths, as detailed in a study from the New England Journal of Medicine.

Additionally, there have been at least three other outbreaks in Argentina since 1996 demonstrating similar transmission paths. For example, one outbreak in 1996 involved 16 people, another in 2002 had 13 linked cases, and yet another in 2014 reported three cases.

CIDRAP News: So, is person-to-person transmission likely?

Michael Osterholm: Yes and no. There were over 100 hantavirus cases reported in Argentina last year, yet there were no instances of person-to-person transmission noted. While it’s uncommon, such transmission can occur, often linked to superspreaders—individuals who transmit the virus at notably higher rates for unclear reasons.

This phenomenon reminds us of the cases seen during the SARS and MERS outbreaks, where a small number of individuals can significantly drive the spread of an outbreak.

A relevant example is a study where a woman who contracted hantavirus in Argentina returned to Delaware and potentially exposed over 50 people, none of whom got infected. These insights suggest that the situation aboard the cruise ship may be self-limiting, as not every person poses the same transmission risk. Unfortunately, the current approach treats everyone in quarantine as if they are superspreaders, which may not be accurate. We won’t know for a few weeks who, if anyone, actually is one.

Air Circulation and Potential Asymptomatic Spread

CIDRAP News: The fact that this involves a cruise ship has led to comparisons with COVID-19. What are your thoughts?

Michael Osterholm: From a ventilation perspective, cold-water cruise ships prioritize heating over cooling. Unlike tropical cruise ships, this environment poses different challenges.

These vessels often circulate large amounts of air, which could explain cases where individuals weren’t in close contact yet contracted the virus. It’s crucial to consider who has been exchanging air, a point that doesn’t seem to be getting enough attention.

CIDRAP News: There have been discussions about asymptomatic transmission in this outbreak. What’s your perspective?

Michael Osterholm: We’re really not sure; it’s possible that someone could transmit the virus within 24 hours before showing symptoms. So far, there have been 10 cases among over 160 contacts—excluding Patient Zero—yielding a low attack rate of about 6%. If I were to imagine a typical transmission scenario on a cruise ship, I’d expect rates could be dramatically higher, around 50% to 60%.

While I extend my sympathies to those affected, I don’t believe this outbreak constitutes a major crisis. To my knowledge, there haven’t been any infections linked to those who disembarked the ship early.

A Look Ahead

CIDRAP News: Regarding those who left the ship before the outbreak was acknowledged, why aren’t they undergoing extensive quarantines like other individuals in the U.S.?

Michael Osterholm: The inconsistency in response is concerning and can undermine credibility. One challenge is that precise science is lacking.

People are fixating on the 42-day quarantine when, in reality, the median incubation period is about 18 days. This suggests that half of the cases would likely arise within those first 18 days after exposure.

The initial infected passenger boarded the ship roughly 30 days prior, and his timeline indicates he was likely contagious during his first week. Thus, it seems unlikely that we’ll see a significant increase in cases sourced from the ship.

While there could be enhanced transmission due to a superspreader, not every infected individual will act in that manner. Many tend to jump to conclusions solely because of the cruise ship context, especially since the COVID-19 pandemic involved similar vessels. However, current evidence does not suggest this will escalate into a widespread pandemic. I anticipate that this situation will resolve itself within the next 10 to 14 days.