An article concludes that there has been human-to-human transmission among close contacts since the middle of December 2019.
On January 31, 2020, the US Department of Health and Human Services (HHS) declared a public health emergency in response to the outbreak of a novel coronavirus (2019-nCoV), while noting that the risk to US residents is still low.
Before the HHS declaration, the World Health Organization announced that 2019-nCoV would be considered a public health emergency of international concern.
2019-nCoV first came to the attention of Chinese public health officials in December as “pneumonia of unknown etiology,” a surveillance category established after the 2003 severe acute respiratory syndrome (SARS) outbreak.
Now, investigators have published details of the first 425 cases in The New England Journal of Medicine. The article includes epidemiologic characteristics and transmission dynamics of the initial 2019-nCoV cases, concluding that there has been human-to-human transmission among close contacts since the middle of December 2019.
Evidence was obtained from local health authorities and the National Institute for Viral Disease Control and Prevention, a division of the Chinese Center for Disease Control and Prevention. Additionally, the Chinese Center for Disease Control and Prevention epidemiology teams acquired data through interviews of infected persons, relatives, health care workers, and close contacts.
Information on dates of illness onset, visits to clinicians, hospitalizations, and clinical outcomes was obtained. The epidemiology teams also investigated exposure to any animals, particularly those said to have been available at the Huanan Seafood Wholesale Market in Wuhan.
Case samples were tested for coronavirus RNA at biosafety level 2 facilities at the provincial Hubei Centers for Disease Control and then at the National Institute for Viral Disease Control.
The epidemiology team found that while the majority of cases reported early on were related to exposure at the Huanan Seafood Wholesale Market, there was an exponential increase in non-linked cases by late December.
The median age of the first 425 cases was 59 years, with a range of 15 to 89 years. The majority of cases, 240 (56%), were documented in men.
Patients from the earliest period of the outbreak were the most likely to be male, younger, and report a visit to the Huanan Seafood Wholesale Market.
In 10 closely examined confirmed cases, the mean incubation period was estimated to be 5.2 days.
The first US case of 2019-nCoV occurred in an individual who had traveled to Wuhan and was asymptomatic when arriving back in the United States.
The mean duration from onset of illness to a medical visit for the 45 patients from before the closure of the Huanan Seafood Market on January 1, 2020, was 5.8 days. For the 207 patients with illness onset between January 1 and January 11, the mean time until a clinical visit was 4.6 days. A sizable minority, 27% of patients, sought medical attention within 2 days after illness onset.
“Our preliminary estimate of the incubation period distribution provides important evidence to support a 14-day medical observation period or quarantine for exposed persons,” the report authors wrote.
The study team estimated that on average, each patient has spread infection to 2.2 other people. While some health care workers have been infected, the investigators report that the proportion has not been as high as in the SARS outbreak.
In order to control the outbreak, the reproductive number (the number of people subsequently infected per patient) will need to drop below 1.0.
Overall, cases were found to be doubling in size every 7.4 days in Wuhan, China, at the time of publication on January 29, 2020.
“Future studies could include forecasts of the epidemic dynamics and special studies of person-to-person transmission in households or other locations, and serosurveys to determine the incidence of the subclinical infections would be valuable,” the authors concluded.