What Do We Know About How Hantavirus Spreads?

Experts are relying heavily on a paper about superspreader events in Argentina to understand transmission dynamics of the Andes virus at the center of the hantavirus cruise ship outbreak.

In that paper, published in 2020 in the New England Journal of Medicine (NEJM), spread was driven by three symptomatic people who attended crowded social events. All of them were in the prodromal phase of illness — raising concerns that people may be at their most infectious early on in their disease.

The authors of the paper also warned that they believed the virus spread via airborne particles, not just droplets.

“On the basis of both the epidemiologic and genomic investigations of person-to-person transmission events, it appears that inhalation of droplets or aerosolized virions may have been the routes of infection,” they wrote.

Some experts have been pushing to acknowledge that airborne transmission is likely in this case. Joseph Allen, DSc, MPH, of the Harvard T. H. Chan School of Public Health in Boston, wrote in The Atlantic that public health officials “have to be more honest and more humble about how this virus actually spreads.”

“If people mistakenly believe transmission relies only on ‘prolonged close contact,’ they may take risks they will soon regret,” Allen wrote.

He stated that public health got it wrong in the early days of COVID, claiming the SARS-CoV-2 virus only spread by fomites and droplets. However, he and his team conducted a modeling study of transmission aboard the Diamond Princess, the cruise ship that had one of the earliest outbreaks of COVID-19.

They determined that 90% of spread occurred through aerosols, not contaminated surfaces, he wrote.

Now, he doesn’t want public health officials to be slow on the uptake once again. He points to the NEJM paper, noting that one patient was infected “after simply crossing paths with someone who was ill.”

Indeed, the supplemental information in the paper contains a diagram of the seating chart of the party where the first patient infected five other people. While two of those people sat close to the patient, two sat at adjacent tables and were more than 6 feet away — and one was at a table more than 8 feet away. That person and the symptomatic patient “crossed paths on the way to the restroom but did not make any physical contact,” the paper stated.

The spouse of the index patient had a fever while she attended his wake, and 10 people who attended that wake and were in close contact with her became sick. Another patient likely infected six others during the early phase of his illness because of his active social life, the researchers reported.

In total, 34 people were infected and 11 died. The incubation period ranged from 9 to 40 days, with a mean time of 23 days.

Interestingly, there were no nosocomial infections among healthcare workers who had been in direct or close contact with the patients. About 82 healthcare workers were exposed to symptomatic patients with confirmed Andes virus infection at one hospital. Only a small number of the 45 people who worked in the intensive care unit and emergency department used any form of personal protective equipment while they were in direct contact with patients — suggesting there’s less transmission risk in the later stages of disease.

Donald Milton, MD, DrPH, of the University of Maryland School of Public Health in College Park, said in an interview on the “Ground Truths” Substack that experts should assume there is airborne transmission until proven otherwise.

“We really need to start from a precautionary position … and assume that [airborne transmission] is part of what’s going on, and then we can back off as we get more evidence,” he said.

Andes virus is the only known hantavirus to be able to transmit human-to-human. The chief strain in the U.S., Sin Nombre virus, does not transmit this way. Instead, the predominant mode of transmission is via aerosolized rodent droppings — for instance, someone sweeps a basement floor, stirring up those droppings, and becomes infected.

There’s also little chance that this current outbreak will pose any risk of infection to the public. Passengers who were repatriated from the MV Hondius earlier this month have been asked to remain at the National Quarantine Unit in Omaha until May 31. Other Americans who returned from the ship in April have been advised to effectively quarantine at home and are being monitored on a regular basis by state public health departments.

Thus, experts have few concerns about onward transmission. Nonetheless, it could happen if people being monitored at home develop symptoms and, like in the Argentina outbreak, spread it to others early on in their illness.