Doctors warn some recent hantavirus test results may be false positives, call for retesting

Doctors and public-health officials are rechecking some hantavirus test results linked to the MV Hondius cruise-ship outbreak after at least one U.S. case initially treated as positive later appeared not to show evidence of infection. A May 20 YouTube segment from Fox News said clinicians were examining possible false positives in recent testing tied to the outbreak. WHO had already reported on May 13 that one U.S. passenger had an “inconclusive” result, with one positive and one negative test from two laboratories, and was being retested. The broader outbreak itself remains documented. CDC said in a May 8 Health Alert Network notice that WHO had been notified on May 2 of a cluster of severe acute respiratory illness aboard the ship and that WHO confirmed Andes virus on May 6. WHO said on May 13 that 11 cases, including three deaths, had been reported, with eight laboratory-confirmed Andes virus infections, two probable cases and one inconclusive case. (youtube.com) ### Which result is drawing the most scrutiny? ABC News reported on May 15 that Dr. Stephen Kornfeld, an American physician who had been aboard the MV Hondius, initially tested positive, was admitted to the University of Nebraska Medical Center biocontainment unit, and later tested negative. Kornfeld told ABC News there was “no evidence that I’ve had hantavirus.” (cdc.gov) Dr. Angela Hewlett, medical director of Nebraska’s biocontainment unit, told ABC News, “I suspect that the initial test was a false positive.” Hewlett said follow-up serology did not show evidence of prior exposure or prior infection and added, “it looks like he has not had this illness at all thus far.” ### Why can hantavirus tests produce conflicting answers? (abcnews.com) CDC guidance says commercial hantavirus assays can produce false-positive results and should be interpreted carefully. A CDC training document says antibodies can cross-react between different hantavirus species and notes that commercial assays can yield false positives, while CDC ELISA testing is described there as highly sensitive and specific. (abcnews.com) WHO’s Andes virus laboratory guidance also says serologic testing can require caution. The guidance says an IgM positive result can confirm acute disease, but potential cross-reactivity with co-circulating hantaviruses should be considered in context, and repeat testing should be considered 24 to 48 hours later if clinical suspicion remains high despite an initial negative result. (stacks.cdc.gov) A University of Washington laboratory test guide says a positive hantavirus IgM result paired with a negative Sin Nombre virus-specific IgM can indicate either a different hantavirus or false-positive reactivity. The same guide says a small number of positive IgM results can be falsely reactive in association with acute cytomegalovirus or Epstein-Barr virus infection. ### Does this mean the cruise-ship outbreak was not real? (iris.who.int) WHO’s May 13 outbreak notice says no. WHO reported eight laboratory-confirmed Andes virus cases among passengers, plus two probable cases, and said all laboratory-confirmed cases were confirmed for Andes virus infection. CDC’s May 8 advisory likewise treated the outbreak as a real multi-country cluster caused by Andes virus, while saying the risk of broad spread in the United States was “extremely unlikely at this time.” The agency said it was working with federal, state, local and international partners on repatriation, monitoring and clinical guidance. (dlmp.uw.edu) ### What are officials and clinicians doing next? (who.int) California’s health department said on May 11 that its Viral and Rickettsial Disease Laboratory had a validated rRT-PCR hantavirus assay that should also detect Andes virus and that it was fast-tracking testing capacity as part of the national response. The bulletin told laboratories to use heightened biosafety measures and risk-based specimen handling. (cdc.gov) WHO said the inconclusive U.S. case was being retested, and CDC said public-health agencies were continuing exposure assessments and monitoring of Americans linked to the ship. The next concrete updates are likely to come through WHO outbreak notices, CDC advisories, and statements from hospitals and laboratories handling repeat tests. (who.int) (cdph.ca.gov)