A 20-year-old woman in Taiwan has achieved the dubious distinction of being the first patient known to have been sickened by a strain of bird flu known as H6N1.
The woman, who became ill in May, appears to have made a full recovery, according to a report published Wednesday by the journal Lancet Respiratory Medicine. But her case raises important questions that investigators are still trying to answer, including: How did she contract the flu? And: Does this make humans more vulnerable to a bird flu pandemic?
Let’s start with what researchers do know.
The unidentified woman was in good health before she came down with a fever and a cough on May 5, according to the journal report. The next day, she went to a hospital emergency room after her fever spiked. She was sent home. The day after that, her high fever prompted a visit to another hospital E.R., and once again she was sent home. Later that evening, she returned to the second E.R. because she was having trouble breathing. She was admitted to the hospital in the early hours of May 8.
X-rays revealed that she had a lower respiratory infection, but throat swabs failed to turn up signs of known influenza strains. Tests were also negative for Legionnaire’s disease and mycoplasma pneumonia. Doctors treated her with oseltamivir (Tamiflu) and levofloxacin (Levaquin) and her symptoms began to improve by May 9. She was discharged from the hospital two days later. A follow-up X-ray taken on May 17 showed that her respiratory infection had cleared up.
The woman may have returned to her normal life, but researchers from Taiwan’s Centers for Disease Control in Taipei and several hospitals and medical schools continued to investigate her case. They used a genetic test called real-time RT-PCR and got a match for H6N1 influenza.
A more detailed genetic analysis of the eight genes that make up the H6N1 virus revealed that seven of the genes were closely related to a flu strain isolated from Taiwanese chickens this year. The eighth gene was most closely related to another strain found in Taiwanese chickens in 2002. Versions of the H6N1 that sickened the woman have been infecting chickens in Taiwan since 1997, according to the report. (Other versions of H6N1 have been “prevalent” in chickens there since 1972, the researchers noted.)
It is still not clear how the virus was able to jump from chickens to the 20-year-old woman. She was a clerk at a deli and didn’t have any contact with chickens, live or dead. She hadn’t been traveling in the three months before she got sick.
The researchers identified 36 of her close contacts, including family members, co-workers and the people who treated her in the two hospitals. Six of these people became ill with fevers or respiratory infections (including one of the doctors who treated several patients with respiratory infections but did not wear a surgical mask or take other standard precautions). But none of them tested positive for influenza.
A family that lived near the woman kept a flock of 60 ducks, chickens and geese. The woman said she hadn’t been in contact with the birds for at least a year, but the researchers tested eight samples of bird stool anyway. All of them were negative for flu.The researchers will keep looking for clues.
“The investigation of the transmission pathways that caused the patient’s infection did not reach a clear conclusion,” they wrote in Lancet Respiratory Medicine. “Because understanding the transmissibility of a novel influenza virus is of major importance to public health, further field and laboratory investigations are warranted.”
Seasonal flus – the kind you can protect against with a flu shot – are of the H1, H2 or H3 varieties. Other flus with H5, H7, H9 and H10 genes have turned up in humans too. Now an H6 strain joins the list.
“Each person infected with an animal influenza virus is judged a threat to public health, because the influenza pandemics of the past 100 years have all emerged from animals,” Marion Koopmans, a virologist at the National Institute for Public Health and the Environment in Bilthoven, Netherlands, wrote in a commentary that accompanies the study. “The question again is what would it take for these viruses to evolve into a pandemic strain?”