US hantavirus case turns out to be a false positive, outbreak count drops to 10
In a coordinated statement this week, the World Health Organization and the US Department of Health and Human Services announced that a hantavirus case reported among MV Hondius passengers in the United States last week has been reassessed as a false positive after second-round testing. The confirmed outbreak total has been revised from 11 to 10 cases.
The case revised as a false positive had initially returned a reactive result on the first PCR analysis run at a CDC laboratory for returning passengers. Confirmatory virus neutralisation and IgM/IgG titre testing showed that the individual did not have an active hantavirus infection. A CDC spokesperson said the false positive could be associated with laboratory contamination or reagent reading.
The WHO bulletin issued on Friday 16 May announced that the operation to safely transfer MV Hondius passengers off the vessel had been completed. The ship had been quarantined in the south Atlantic on 19 April after Andes hantavirus cases were reported, then routed to the Canary Islands for quarantine; the last passengers were handed over to regional health services in mid-May.
The updated overview lists ten affected countries: the United States, the United Kingdom, France, Germany, Spain, Canada, the Netherlands, Australia, Japan and South Africa. Some cases remain under monitoring. With the US case removed from the count, the national figure has been moved into a 'pending' category in which the future of one individual is still being assessed.
Work done by South Africa's Department of Health last month confirmed that the strain responsible for the outbreak is the Andes hantavirus, native to South America. The Andes strain is the only known hantavirus strain considered to carry a rare potential for human-to-human transmission. That made the six-week self-isolation protocol applied in Europe and North America for returning MV Hondius passengers especially important.
The WHO stressed that the outbreak is under control but said that monitoring would continue for 90 days. The follow-up window aims to evaluate the risk of late-onset hantavirus cardiopulmonary syndrome. The MV Hondius outbreak's case-fatality rate is approximately 20%; two passengers died, one in Chile and one in the Netherlands.
The US CDC said that the false positive did not change the curve of the outbreak but that laboratory capacity and confirmation protocols would be reviewed. The CDC's Division of Infectious Diseases said that announcing the reclassification in mid-May had required 'completing the necessary second confirmations.'
MV Hondius operator Oceanwide Expeditions has said in statements since the outbreak began that the vessel would have its rodent-control protocols reviewed and that all passenger cabins and crew areas would be sanitised before the next sailing. The company has not commented further on insurance and legal proceedings.
For comparison, hantavirus pulmonary syndrome (HPS) in the United States is generally caused by the Sin Nombre strain rather than Andes; that strain has no record of human-to-human transmission. With an average of 30 to 40 cases reported annually, Sin Nombre HPS has an estimated case-fatality rate of about 38%.
The next update on the outbreak is expected from the WHO next week. Independent reviewers have recommended that a post-event evaluation document on border controls, on-ship screening protocols and transfer processes be published in the coming month.