China links COVID outbreak to man jogging through park; Scientists are skeptical
In the early morning of August 16, a 41-year-old man in southwest central China’s Chongqing municipality got up and went jogging along a lake in a local outdoor park—what should have been a pleasant, if not unsightly, outing. But what really happened during that 35-minute jaunt has now sparked international alarm and debate, with some scientists questioning China’s stunning statement.
According to the Chinese Center for Disease Control and Prevention, an unmasked man infected 33 unmasked park visitors and two unmasked park workers with the omicron subvariant BA.2.76 coronavirus during his short ride. The agency claimed the transmission occurred in brief outdoor encounters as he trotted past people on a four-meter-wide track. Many others are infected without any close encounter. Twenty of the 33 infected park visitors became infected simply by visiting the outside areas of the park that the runner had previously passed through, including the front door. Two infected workers, meanwhile, quickly spread the infection to four other colleagues, bringing the total number of runners in the park to 39.
To support these unusual conclusions, the CCDC cited case interviews, park surveillance footage, and SARS-CoV-2 genetic data, which purportedly link the cases but are not in the report.
The report’s claims, if true, suggest that a significant update is needed to our current understanding of the risk of SARS-CoV-2 transmission. Although outdoor transmission is known to be possible, it is considered far less likely than indoor transmission, where viral particles can float in stagnant air and accumulate over time indoors. Outdoor encounters that are transient in particular are not considered a significant risk, since the huge volumes of moving air quickly disperse infectious doses of viral particles. For the same reason, SARS-CoV-2 is not thought to linger in threatening clouds outdoors after an infected person wakes up.
So far, experts outside China are not revising their opinion on the risks of transmission, citing missing genetic data in the report and other questionable conclusions.
Given China’s strict “zero COVID” strategy, the CCDC directly dismissed the possibility that the infections were part of an undetected outbreak in the wider community, calling exposure to the runner (aka “patient zero”) the “only possible exposure.”
The CCDC claims genetic data ties all the cases together, showing that patient zero was the source of 39 infections. Specifically, they report that 29 of 39 cases had “exactly the same sequenced gene as the null patient; 5 cases had the mutation site added to the null patient’s gene sequence; and the other 5 cases could not be sequenced due to unqualified samples.” But there is no sequencing data included in the report and it is unclear what sequencing was actually done to support their claims.
“If they had sequence data showing that 29 cases had genomes identical to ‘patient zero,’ that would suggest that all the cases came from a single source,” virologist Angela Rasmussen told Ars. Rasmussen is a researcher at the Vaccine and Infectious Diseases Organization at the University of Saskatchewan and an affiliate of Georgetown University’s Center for Global Health Science and Security.
“But,” she said, “it’s not clear whether they did whole-genome sequencing of all cases, what sequencing platform they used (Illumina vs Nanopore), etc.” The report only mentions “gene sequencing”, which may suggest only partial genome sequencing, not “whole genome sequencing” which would definitively indicate a direct link between the cases. Without knowledge of the data and sequencing methods, it is impossible to confirm whether the runner was the source.
The CCDC also offers a puzzling explanation for how the running Patient Zero got infected in the first place.
According to the CCDC, the man became infected due to unclear “exposure to the contaminated environment of the aircraft.” The man traveled from Chongqing to the northern city of Hohhot on August 11 and returned to Chongqing on August 13 – three days before the run. There were no known cases of SARS-CoV-2 on board any flight that could explain the man’s infection. However, the return plane carried four passengers who tested positive for SARS-CoV-2 the day before, on August 12.
On August 12, four passengers from Tibet took a plane from Chongqing to Hohhot and later tested positive in Hohhot. The plane, meanwhile, was not disinfected after their flight, and the man from Chongqing boarded the next day and sat (in seat 33K) near where the three infected passengers sat (seats 34A, 34C, 34H). It is not clear how a person could have been infected in this way – SARS-CoV-2 is not known to linger in the air for that long, and transmission from contaminated surfaces is rare. Moreover, the report does not indicate that other passengers on the flight also became infected, including people who were actually sitting in the same seats as the passengers from Tibet. But patient zero was infected with BA.2.76, which had been circulating in Tibet, prompting the CCDC to conclude the link.
“I think it’s also highly doubtful that ‘patient zero’ was infected on that plane,” Rasmussen said. “I noticed that the previous flight with passengers who were the alleged source of the infection came from Chongqing—this might suggest a cryptic spread of BA.2.76 in Chongqing, not (only) Tibet as the paper claims. In this case, if the whole bunch people in Chongqing has BA.2.76, the sequencing data may only point to a much larger outbreak in Chongqing, but you would need actual sequencing data to really understand what is going on.
“The bottom line: any claims about what the data actually show depend on actually putting the data to work,” she said. – Otherwise, these are just guesses.