One of the key questions in the fast-growing novel coronavirus (2019-nCoV) outbreak has been the possibility that asymptomatic people transmit the virus to others, and German researchers yesterday who described a workplace illness cluster suggest that it probably played a role in virus spread.
The report involves Germany's first patient, whose illness was announced on Jan 28. German researchers detailed their investigation findings in a letter to the New England Journal of Medicine.
Earlier this month, Chinese health officials said they suspected a role for transmission in the outbreak when a patient has no obvious symptoms, but experts have said they are waiting for more evidence. Asymptomatic transmission is known to occur with other respiratory viruses, but it isn't thought to be a major driver of disease spread.
Reassessment of transmission dynamics?
The man had attended work meetings with a Chinese colleague who became ill on the plane as she returned home to Shanghai, where she was diagnosed as having 2019-nCoV.
On the day after she tested positive, she reached out to the German company, and contact tracing began. The man—who had been sick a few days before with fever and cough—was now fever-free and well, yet he tested positive for the virus. He had not been out of Germany in the 14 days before his symptoms began.
Two days later, three company employees tested positive for 2019-nCoV, but only one had contact with the Chinese woman, who is considered the index patient. The other two had contact only with their German coworker, the first to get sick.
All of them are hospitalized in isolation, and none have severe infections. Germany reported three more cases linked to the workplace cluster today, involving two employees who had contact with the earlier patients and a child of one of the employees.
The authors wrote that the first patient's clinical course is notable, not only because it signifies local transmission, but also because the Chinese woman apparently transmitted the virus during the incubation period.
"The fact that asymptomatic persons are potential sources of 2019-nCoV infection may warrant a reassessment of transmission dynamics of the current outbreak," they wrote.
Also, the German man who was infected first had a high sputum viral load, even though he was recovering, which they said raises concerns about prolonged 2019-nCoV shedding after recovery.
Asymptomatic…or subclinical?
Isaac Bogoch, MD, an infectious disease physician and researcher at the University of Toronto, said on Twitter today that the clinical spectrum can range from asymptomatic to subclinical to clinical, and the question is who is more likely to spread the virus to a greater number of people? People with subclinical infections may be shedding the virus and passing it to others, but might not be sick enough to seek medical care, he said.
He noted that the index patient reported to be asymptomatic later went on to become ill, a pattern seen with other respiratory infections.
He said typically it's symptomatic people who spread respiratory viruses by coughing, but it appears that asymptomatic people can transmit disease, as well. "But in general, when it comes to respiratory infections, those with symptoms transmit more," Bogoch said.
Quickly identifying symptomatic people can help prevent transmission to others, but the process depends on public education, public health, and healthcare capacity, he added.
Learning about 2019-nCoV requires being humble and open-minded, Bogoch said. "We do not have all the answers. We are learning more about the biology of this virus, its transmission dynamics, and clinical spectrum every day."
See also:
Jan 30 N Engl J Med letter
Jan 28 CIDRAP News story "WHO seeks to answer nCoV unknowns as more local spread noted outside of China"
Jan 31 Isaac Bogoch Twitter thread
