Pathologists respond to hantavirus concerns

On May 12, the College of American Pathologists hosted a media briefing on hantavirus in response to the outbreak of the Andes strain of the virus on the luxury cruise ship MV Hondius. Panelists included:

• Qihui “Jim” Zhai, MD, FCAP – President, College of American Pathologists
• Mara Jana Broadhurst, MD, PhD, FCAP – Member, CAP Microbiology Committee; Associate Professor, University of Nebraska Medical Center
• Bobbi S. Pritt, MD, MSc, FCAP – Professor of Laboratory Medicine and Pathology and Chair of the Division of Clinical Microbiology at Mayo Clinic
• Benjamin Bradley, MD, PhD, FCAP – Vice Chair, CAP Microbiology Committee and Medical Director of high consequence pathogen response, virology, and molecular infectious disease at ARUP Laboratories

In the opening of the briefing, Dr. Pritt said, “In my mind, two of the big things that have come out of this so far is that first of all, the importance of public health in contact tracing, quarantining exposed individuals, and isolating those with symptoms. And then also as a pathologist, I wanted to emphasize the importance of laboratory testing — not just serologic testing, which is the detection of IgM and IgG antibodies, and considered the gold standard method, but also our advanced techniques like PCR and next-generation sequencing, which allowed us in this case to very quickly identify the cause of this outbreak…we cannot emphasize enough the importance of pathologists and laboratory medicine in effectively managing this outbreak.”

Some of the questions and answers follow. The full presentation can be viewed here: Hantavirus Update: Facts, Risks, and What Matters Now.

Question: Many people have responded to the hantavirus outbreak through the lens of a global pandemic that impacts all of us. Can you respond to the concerns people have about the virus and its risks relative to the actual risks?

Dr. Pritt: Those who had close contact with infected individuals, they have a right to be concerned. We definitely want to respect the virus that has up to a 40% case fatality rate. Those that are truly exposed are at heightened risk. We don’t want to trivialize it. We also don’t want to catastrophize it. This is not a pandemic setting where we have a high transmission rate person to person. We know it really takes prolonged person to person contact to transmit this virus. And we really want to emphasize the main points that outside of these close contact settings, we’re not seeing the sustained community transmission that would concern us.

Dr. Broadhurst: This virus is an endemic virus to South America that has been studied for decades, so there is more information at the outset that helps us to understand how this virus is transmitted and what the risks are. More than what we had at the start of the COVID-19 pandemic. This is not a virus that is transmitted easily or through casual interaction as we have found with viruses like influenza and SARS-COV2.

Dr. Bradley: Something else that is interesting about this case, because it did happen on a cruise ship, is if you look back on the literature of infectious diseases — cruise ships have been the site of outbreaks where we have been able to get R-Naught value (a sense of how many people are at risk of getting infected by a single individual). Norovirus has an incredibly high incidence on cruise ships, which causes gastrointestinal symptoms. Even early in the COVID pandemic, cruise ships actually gave us some good data about the R-Naught value of COVID as well. To echo Dr. Broadhurst and Dr. Pritt, we’re just not seeing that high transmissibility between humans on this cruise ship that would make this thing a pandemic or an epidemic happening from this outbreak.

Question: Can this virus be spread by an asymptomatic person?

Dr. Pritt: We do not have evidence of transmission of this virus in asymptomatic people. We do know that it’s appropriate to take precautions in individuals who have been exposed and may develop symptoms. So for those individuals who are either under monitored quarantine in quarantine facilities or those who are under monitoring and quarantining at home, there has been an understanding that the most important thing that people should be aware of is that symptoms can develop within a pretty long incubation period…as long as six weeks. If symptoms develop, as has been noted, this is a very serious infection and those symptoms can escalate quickly, and it’s very important that people have access to higher levels of care.

Question: For the patients being monitored, do you recommend regular, routine testing for all of them, or is that only necessary when symptoms appear?

Dr. Broadhurst: Testing is an individualized decision between the clinicians and the individual who has had an exposure.

Dr. Bradley: The test we use for this is serology. Because of all the different strains of hantavirus that exist, there can sometimes be risk of cross-reactivity or false positive tests. So if we’re testing people who already have a very low positive or no chance of having the disease, then if we do see a “positive” result from a test like that, we know it could be a false result and we don’t want people to experience any more anxiety about this than they need to. Also understand who is appropriate to be tested. Really, it’s for the patients who we have clear epidemiological links to cases right now.

Question: What is the CDC’s, state’s, and local public health laboratories’ ability to test and sequence this strain of hantavirus or others? And should clinical laboratories be contributing to this testing effort?

Dr. Pritt: There is limited testing. Mostly specialized reference laboratories, state and public health laboratories, and the CDC. I work for a reference laboratory — Mayo Clinic Laboratories. We do have a hantavirus serology test that we’re working on making public so that people can get it through a physician’s order, but the testing is not readily available outside those referral settings.

Dr. Broadhurst: As with many viral infections, both serology and PCR-based detection are in play for diagnosis of this disease. Serology is most available, and that is the test offered by the CDC. So detection of IgM, which is an early indicator of immune response to the virus and is sensitive for diagnosing the infection once symptoms have developed is being made available by the CDC to select reference laboratories. PCR-based testing is also a tool in the toolkit for diagnostic testing for this virus and is being developed by a couple laboratories that are engaged in the close monitoring and care of exposed individuals.

I will note, we do have an endemic hantavirus here in North America, Sin Nombre virus. And so, some laboratory testing tools have been developed to diagnose Sin Nombre hantavirus. There are some similarities between these viruses that allow for some utilization of these tools for detecting both Sin Nombre and Andes hantavirus infections. So there is some preexisting capacity in our laboratory tools available.