Human-to-human transmission of the new coronavirus has occurred since mid-December among close contacts in China, researchers reported today in The New England Journal of Medicine.
The finding was based on data from the first 425 laboratory-confirmed cases of the virus from Wuhan, the city in Hubei province at the center of the outbreak of 2019-nCoV.
The researchers from several institutions in China, including the Chinese CDC, also described some characteristics of infected patients and estimated the epidemic doubling time and the basic reproduction number — or R0 (R naught) — of the infection.
China has reported more than 7,000 confirmed cases and 132 deaths from the coronavirus, in addition to more than 12,000 suspected cases. There also have been at least 68 confirmed cases in 15 other countries, according to WHO, including five in the United States.
According to the new study, the median age of the first 425 patients was 59 years, and 56% of patients were male. Few of the early cases occurred in children — none in children younger than age 15 years — and almost half were in patients aged 60 years or older. The researchers speculated that children may be less likely to be infected or may show milder symptoms.
Most illnesses — 55% — that began prior to Jan. 1 were linked to the Wuhan seafood and animal market where the outbreak is thought to have originated.
The researchers estimated the mean incubation time to be 5.2 days (95% CI, 4.1-7) and the estimated epidemic doubling time early in the outbreak to be 7.4 days. They estimated the mean serial interval to be 7.5 days (95% CI, 5.3-19) and the R0 to be approximately 2.2 (95% CI, 1.4-3.9), “meaning that, on average, each patient has been spreading infection to 2.2 other people,” they wrote. The authors noted that the R0 of SARS was estimated to be around 3, “and SARS outbreaks were successfully controlled by isolation of patients and careful infection control.”
“It’s great to see a peer-reviewed estimation of R0, given the oversized importance that has been placed on this metric by some of the popular press and on social media,” Angela Rasmussen, PhD, an associate research scientist at the Columbia University Mailman School of Public Health Center for Infection and Immunity, told Healio. “R0 is heavily context-dependent and so should be interpreted cautiously. This estimate of R0 2.2 is consistent with a lot of the other figures I’ve seen.”
A WHO emergency committee is meeting for a third time on Thursday to determine if the outbreak constitutes a Public Health Emergency of International Concern (PHEIC). The body was split on declaring a PHEIC last week; WHO Director-General Tedros Adhanom Ghebreyesus, PhD, MSc, opted not to declare one. – by Gerard Gallagher
Disclosures: The researchers report no relevant financial disclosures. Rasmussen reports no relevant financial disclosures.