Hong Kong residents experienced an unwelcome blast from the past on Nov. 18. A 59-year-old woman in the city contracted H5N1 avian influenza — the first confirmed case in Hong Kong since 2003. It's not clear how she became sick. She traveled to China Oct. 23 to Nov. 1, visiting several cities — and according to the Hong Kong government, she spent time at a live poultry market in mainland China and ate chicken while she was there. She started showing flu symptoms the day after she returned to Hong Kong, and was admitted to the hospital with a high fever on Nov. 14, and she's in serious condition.
How worried should we be? As a virus, H5N1 is a lot deadlier than the H1N1/A swine flu bug that triggered the flu pandemic of 2009-10. Of the 507 human cases of H5N1 that have been confirmed by the World Health Organization (WHO), 302 have died. At the same time, what's kept H5N1 from creating its own, far deadlier pandemic is the fact that the virus doesn't seem to spread easily between human beings. With the exception of a few, scary cases, nearly every person who has contracted H5N1 has done so directly from a sick bird. That's part of the reason why the disease has only struck in Asia and parts of the Middle East and Africa, where live poultry markets are common and where there is often little separation between a backyard chicken farmer and his birds. (More on Time.com:More Wisdom From a Long-Ago Plague)
While it may have been overshadowed by H1N1/A, the truth is that H5N1 never went away. The virus has still been popping up sporadically in parts of Southeast Asia (especially Indonesia, which has recorded by far the most cases), China and the Middle East, often at the same time that outbreaks had been detected in avian populations. (H5N1 doesn't spread easily among people, but it can burn like wildfire through birds, and infect other animal species, including tigers.) The fact that a Hong Konger contracted the disease is cause for elevated concern, while not panic — the former British colony was the site of the first confirmed human cases of H5N1, back in 1997, which launched a massive global response to head off what could have been deadly flu pandemic. (Read Erik Larson's great TIME story on Hong Kong's bird flu battle.) Six people would die.
After the 1997 outbreak — which was likely stemmed thanks to a massive cull of 1.5 million chickens in the city to wipe out any trace of the disease — Hong Kong tightened sanitary standard for poultry farms and for the live bird markets popular among its Cantonese residents. (The markets are found everywhere in the city — when I lived in Hong Kong a few years ago, there was a live market just a block away from my high-rise apartment. You could pick a live chicken, have it defeathered and be out in a few minutes.) There another brief outbreak in 2003, but since then the city has been clean of avian flu, even as the virus has repeatedly struck China and its other neighbors. (More on Time.com:Is Your Touch-Screen Dirtier than a Toilet Flusher?)
Still, Hong Kong will always be a hotspot for disease hunters. The city sits on the edge of southern China, which is home to a huge population of people and birds living cheek-to-beak. New flu viruses often — but not always, as we saw with H1N1/A, which seems to have begun in Mexico — first evolve in the friendly confines of southern China. Once the new viruses spread to Hong Kong — home to one of the world's busiest airports — it can jump to every corner of the planet in less than a day. (Although as mainland China itself becomes more and more directly connected to the rest of the world, Hong Kong may no longer be the disease incubator it once was.)
Most likely the Hong Kong case will be a one-off — there has been no indication of human-to-human transmission of the virus, and eight close contacts of the patient are showing no symptoms. Officials have begun checking the city's poultry markets, though no sick birds have been found yet. It's entirely possible, likely even, that she contracted the disease in mainland China, not Hong Kong — though given the fact that China has been far less successful in controlling the disease than Hong Kong, that's not much comfort. The reality is that H5N1 remains a threat, possibly just a few genes away from gaining the ability to spread easily among human beings. And as our muddled response to H1N1 showed, an ever-more connected world hasn't gotten much better at dealing with a global disease.