Public health officials attempting to contain the new coronavirus are trying to figure out how easily it spreads. One key question is whether people who are infected but show no symptoms can infect other people.
A new study from an international team of researchers, posted on a medical preprint site, estimates that two-thirds of the coronavirus infections in Wuhan, China, before the imposition of travel restrictions Jan. 23 were transmitted by people who were not documented as infected.
A report in the New England Journal of Medicine in the past week suggested that the disease reaches peak infectiousness shortly after people start to feel sick, spreading in the manner of the flu. A study published in JAMA on Friday chronicled the case of a 20-year-old Wuhan woman who infected five relatives, even though she never showed signs of illness.
“What we find is that this virus is going to be very difficult to contain,” said Jeffrey Shaman, an infectious disease researcher at Columbia University and co-author of the study posted Monday. “Personally, I don’t think we can do it.”
Experts estimate it takes about a week for the number of infections in a given community to double. Based on that, it probably would take several weeks for a new infection cluster to be picked up by a local health department, said Trevor Bedford, a computational biologist at Fred Hutchinson Cancer Research Center in Seattle. By mid-March, he estimated, officials should know whether there is community transmission and a true pandemic.
Likewise, it’s hard to know what’s up with the novel coronavirus. Scientists in Germany reported a case in the New England Journal of Medicine on Jan. 30 in which a visitor from China without symptoms passed the disease along to a colleague in Munich. But, as Science magazine first reported, that was wrong. The woman actually did have symptoms.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, had cited that case last week at a White House meeting in which health officials announced a quarantine for people returning from the disease’s hotspot in China. He says the errant letter in the journal doesn’t alter his view.
Fauci says he’s been talking to trusted colleagues in China about this issue, and “they told me without a doubt there is some degree of asymptomatic transmission.”
But he says to the extent it’s happening; it doesn’t explain the apparently explosive spread of this disease within China.
The history of respiratory disease is that “asymptomatic transmission is not the main driver of [any] outbreak.”
Even so, Maria van Kerkhove at the World Health Organization says this question is subject of intense scrutiny right now.
The bigger risk could well be from people who have symptoms, but whose illness is mild enough that they don’t stay home in bed. The German man who caught the coronavirus from his Chinese colleague had a brief fever, but went back to work quickly – and spread his infection to other colleagues.
This pattern of infection is similar to that of the flu. “It’s looking more like a really bad influenza than it is a SARS-like disease,” Fauci says.
