News reports speak of a mysterious respiratory illness; scientists investigate; the anxious don face masks; and patients are ushered into quarantine: It's a scenario all too familiar to Hongkongers.
The outbreak of Middle East respiratory syndrome (Mers) is bringing back bitter memories of the 2003 Sars outbreak that claimed 299 lives in Hong Kong and changed the city forever.
But what do Hongkongers needs to know about Mers? And should they fear a devastating outbreak here?
As of Friday, Mers had infected 313 people worldwide and killed 92.
The disease came to international attention in September 2012, when a British-based Qatari who had travelled to the Middle East was discovered to have an acute respiratory infection.
At first, it was feared that Sars had returned, but research by a British team revealed that the two were distinct, but closely related, coronaviruses.
Professor Yuen Kwok-yung, a University of Hong Kong microbiologist and expert on coronaviruses, found at the time that the new virus shared 90 per cent of its genetic sequence with two viruses found in bats in Hong Kong. He believed the new virus had an ancestor in common with the bat diseases.
Back then, Hong Kong authorities said the chances of Mers spreading here were small.
But facts about the virus that have come to light since have done little to ease concerns. In March last year, Dutch researchers worked out how the virus was able to infect human cells and cause severe, potentially fatal damage to the lungs.
The same month, further research by Yuen led him to conclude that the mysterious new virus had the potential to be more deadly and "promiscuous" than Sars and could cause a deadly pandemic if it mutated further.
By August, it emerged that the new coronavirus had developed a year before the first known case, but had circulated unnoticed.
Mers was back in the headlines this week when the World Health Organisation said that the number of cases was on the rise. While the exact source of the disease remained unclear, the WHO found that 75 per cent of the cases had been spread from human to human.
The WHO also expressed concern that two significant outbreaks had occurred in health facilities and infected medical staff.
No human cases have been recorded so far in Hong Kong, the mainland, Taiwan or Macau. But Mers offers a timely reminder of the need for vigilance against deadly diseases in our densely packed city.
Mers is now a statutorily notifiable infectious disease. That means doctors must immediately report any suspected case of the illness to authorities.
But there is still reason to be concerned because the city's public hospitals, suffering with staff shortages and limited resources, may be unable to cope with another crisis.
The fact many of Hong Kong's estimated 250,000 Muslims may visit Saudi Arabia for the holy month of Ramadan in July or join the haj pilgrimage in October has heightened concerns.
Health Minister Dr Ko Wing-man, who was famously forced to take the helm of the Hospitals Authority when its director was struck down with Sars in 2003, believes early quarantine is the way to stop an outbreak.
He is confident surveillance mechanisms are in place. But he also believes the city must remain vigilant. Hongkongers will surely agree.