The notion of a single patient zero is both theatrical and real: In any new epidemic, some unlucky soul seeds the first infection, several links of which are fated to seed chains of their own and spark a viral Big Bang.
By analyzing the genetic material of people who test positive, scientists can trace the lineage of each virus back to a common ancestor, and often to an individual carrier. The first confirmed coronavirus case in the United States was a man who landed at Seattle-Tacoma Airport on Jan. 15, from China. Other introductions came in February, and scientists are now closing in on who, exactly, sparked the outbreak in Washington State.
New York confirmed its first case on March 1, and by that time there were already thousands of infected people walking around, for a week or more. Scientist have found genetic signatures on the viruses studied so far that link them to Europe, likely brought in by some of the millions of people arriving in New York in February, and it is likely that there were multiple introductions that spread widely: patients zero, plural.
The first infected arrivals in a community are not necessarily the ones who light the fuse. In a report published last week, genetic scientists argued that infected people were among both Americans and Europeans in January, but that most of those viruses fizzled out. And French doctors recently reported that a respiratory sample from a man hospitalized near Paris, in late December, tested positive. That virus, too, likely died out. France’s outbreak did not start until many weeks later.
The world’s patient zero, in China, began infecting others in the late fall of last year, the evidence thus far suggests. An analysis of the first 41 confirmed cases, all in people who had visited the same seafood market in Wuhan, indicates that the first hospital admission was on Dec. 16, 2019. The patient first noticed symptoms on Dec. 1, so the infection dates back earlier. Several scientists have estimated that the first outbreak began in late or mid-November, and have inferred a probable common viral ancestor, though additional virus samples could change the picture.