The mystery Wuhan viral ‘pneumonia’ outbreak linked to a wet market has prompted the Hong Kong government to take measures that recall the early days of the Sars emergency in 2003. Amendments to the disease-control law to list the still unidentified virus as a notifiable disease will empower health authorities to isolate patients suspected of having contracted it after visiting Wuhan in central China, and compel doctors to report cases. In the case of Sars, also an unidentified respiratory virus at the time, isolation soon extended to family and close contacts of victims. Health authorities have ruled out Sars (severe acute respiratory syndrome) or other known highly contagious viruses such as bird flu as the threat. But its unknown nature is ample justification for emergency precautions. It also explains why we overcame our usual reluctance to publish a photograph readers might have found confronting. Our page one picture on Monday of a wet market in Wuchang, Wuhan, showed a bloody scene in which a man was cutting up fish in a bowl, near another containing frogs, watched over by a chicken perched nearby. It is not an uncommon scene on the mainland, with birds, fish, animals, frogs and turtles mixed together in wet markets. Amid the spreading outbreak, we published the picture to show how risky it can be. In terms of exposure to viruses and their mutations, it showed a disaster waiting to happen. For example, chickens run free despite the potential danger of deadly bird flu being transmitted. It is no small wonder therefore if a new strain of viral pneumonia has emerged. This is the consensus of experts after ruling out Sars. Thankfully, there is no evidence so far of human-to-human transmission. But while the virus remains a mystery it would be foolish to lower our guard. Vigilance is paramount. The first case was reported only last week but, with the painful experience of Sars not far from the mind, Hong Kong has already stepped up screenings for airport and rail arrivals, and prepared isolation wards for those with symptoms and a travel history to Wuhan. The single most effective step in enhancing such precautions would be greater transparency and more stringent measures on the mainland. That said, there is evidence mainland authorities have learned the lessons of Sars, judging by swifter reaction this time including briefing the World Health Organisation. Less than three weeks ahead of Lunar New Year festivities, transparency and a sense of urgency are critical. Because of the effect of African swine fever on pork production and prices, demand for alternative meat dishes is rising. This can only make hygiene at wet markets complex and challenging. Vigilance is not only the first line of defence, but also it cannot be relaxed.