sick in Shenzhen, he commuted home to another city, Heyuan, and sought medical treatment there at the Heyuan City People’s Hospital, where he infected at least six health-care workers before being transferred to a hospital in Guangzhou, about 130 miles to the southwest. One young doctor who rode to Guangzhou in the ambulance with him also became infected.
Not long afterward, during late December and January, other such illnesses started occurring in Zhongshan, sixty miles south of Guangzhou and just west across the Pearl River Delta from Hong Kong. Within the next several weeks, twenty-eight cases were recognized there. Symptoms included headache, high fever, chills, body aches, severe and persistent coughing, coughing up bloody phlegm, and progressive destruction of the lungs, which tended to stiffen and fill with fluid, causing oxygen deprivation that in some cases led to organ failure and death. Thirteen of the Zhongshan patients were health-care workers and at least one was another chef, whose bill of fare included snakes, foxes, civets (smallish mammals, distantly related to mongooses), and rats.
Authorities at Guangdong’s provincial health bureau noticed the Zhongshan cluster and sent teams of “experts” to help with treatment and prevention, but nobody was really an expert, not yet, on this mystifying, unidentified disease. One of those teams prepared an advisory document on the new ailment, labeling it “atypical pneumonia” (feidian in Cantonese). That was the phrase, a common though vague formulation, used weeks later by WHO in its global alert. An atypical pneumonia can be any sort of lung infection not attributable to one of the familiar agents, such as the bacterium Streptococcus pneumoniae. Applying that familiar label tended to minimize, not accentuate, the uniqueness and potential severity of what was occurring in Zhongshan. This “pneumonia” was not just atypical; it was anomalous, fierce, and scary.
The advisory document, which went to health offices and hospitals throughout the province (but was otherwise kept secret), also supplied a list of telltale symptoms and recommended measures for controlling against wider spread. Those recommendations were too little and too late. At the end of the month, a seafood wholesaler who had recently visited Zhongshan checked into a Guangzhou hospital and triggered the chain of infections that would circle the world.
This seafood merchant was a man named Zhou Zuofeng. He holds the distinction of being the first “superspreader” of the SARS epidemic. A superspreader is a patient who, for one reason or another, directly infects far more people than does the typical infected patient. While R0 (that important variable introduced to disease mathematics by George MacDonald) represents the average number of secondary infections caused by each primary infection at the start of an outbreak, a superspreader is someone who dramatically exceeds the average. The presence of a superspreader in the mix, therefore, is a crucial factor in practical terms that might be overlooked by the usual math. “Population estimates of R0 can obscure considerable individual variation in infectiousness,” according to J. O. Lloyd-Smith and several colleagues, writing in the journal Nature, “as highlighted during the global emergence of severe acute respiratory syndrome (SARS) by numerous ‘superspreading events’ in which certain individuals infected unusually large numbers of secondary cases.” Typhoid Mary was a legendary superspreader. The significance of the concept, Lloyd-Smith and his coauthors noted, is that if superspreaders exist and can be identified during a disease outbreak, then control measures should be targeted at isolating those individuals, rather than applied more broadly and diffusely across an entire population. Conversely, if you quarantine forty-nine infectious patients but miss one, and that one is a superspreader, your control efforts have failed and you face an epidemic. But this useful advice was offered from hindsight, in 2005, too late for application to the fishmonger Zhou Zuofeng in early 2003.
No one seems to know where Mr. Zhou picked up his infection, though presumably it wasn’t from seafood. Fish and marine crustaceans have never been implicated among the possible reservoirs for the pathogen causing SARS. Zhou ran a shop in a major fish market, and possibly his sphere of activities intersected with other live markets, including those that offered domestic and wild birds and mammals. Whatever its source, the infection took hold, went to his lungs, caused coughing and fever, and drove him to seek help at a Guangzhou hospital on January 30, 2003. He remained at that hospital only two days, during which he infected at least thirty health-care workers. His condition worsening, he was transferred to a second hospital, a place that specialized in handling cases