Health authorities in Taiwan today announced the first known human infection with H6N1 avian influenza, in a 20-year-old woman who was sick with pneumonia in May and has since recovered.
The virus was identified at a time when Taiwan officials were on heightened alert for H7N9 illnesses. The woman's novel flu infection first came to the attention of Taiwanese health officials just 2 weeks after the region had identified its first H7N9 case in a man who had recently traveled to China's outbreak area for work.
The woman started having flu-like symptoms on May 5 and was hospitalized 3 days later after her condition worsened, according to a statement from the Taiwan Centers for Disease Control (Taiwan CDC). She was diagnosed with mild pneumonia, and her illness quickly improved after she was treated with oseltamivir (Tamiflu).
Tests on her respiratory specimen at the hospital indicated an unsubtypable influenza A virus, and genome sequencing at Taiwan CDC's National Influenza Center found that the virus was a novel avian-origin H6N1 virus.
The woman was discharged from the hospital on May 11 and has fully recovered. Follow-up serum testing showed an antibody titer of 1:20 on May 24, and a sample collected on Jun 8 showed a 1:40 titer.
An investigation revealed that the woman works at a breakfast shop, had not been out of the country, and had no exposure to poultry or birds.
Of 36 close contacts that were tested, 4 had flu-like symptoms, but none tested positive for the H6N1 virus, according to Taiwan CDC.
Agriculture authorities collected specimens from two poultry farms that were within 1 kilometer of the woman's home, but tests found no H6N1 virus.
Taiwan CDC said it routinely collects specimens from patients who have flu-like illness or unexplained pneumonia. So far this year about 250,000 specimens have been tested and 86,000 viruses isolated and identified. The imported H7N9 strain and the woman's H6N1 strain are the only non-H1N1 or H3N2 subtypes that have been detected.
Health officials who met to discuss the case determined that it was a sporadic one with no evidence of human-to-human transmission.
The H6N1 virus is a low-pathogenicity virus that commonly circulates in domestic birds, and the virus isolated from the woman's respiratory sample closely resembles the virus in poultry, according to Taiwan CDC. Sequencing data suggest it is sensitive to the neuraminidase inhibitors oseltamivir and zanamivir (Relenza).
David Halvorson, DVM, an avian health expert at the University of Minnesota in St. Paul, told CIDRAP News that the woman's infection could represent an isolated event. He added that various avian influenza viruses, or antibodies against them, have been detected in humans, including H7, H9, H10, and H11 strains.
He said the epidemiology of low pathogenicity viruses such as H6N1 across Asia is largely unknown, because they aren't as detectable as highly pathogenic H5N1. However, such viruses are likely to be endemic in the same areas. "The burst of human cases of H7N9 infection in a large geographic area would seem to support that belief," he said.
Michael Osterholm, PhD, MPH, director of the University of Minnesota's Center for Infectious Disease Research and Policy (CIDRAP), which publishes CIDRAP News, said the identification of a single H6N1 infection doesn't automatically signal the emergence of a new type of flu. "I think as we begin to look more intensively at influenza-like illness surveillance, we may find other situations where there are just one or two occurrences," he said.
However, the case is a reminder that health officials need to keep a close eye on the viruses that are circulating, Osterholm said.
"The billion dollar question is when are these of real public health importance? I don't think we know yet," he said. "We have to keep our eyes open."
Jun 21 Taiwan CDC statement