Early information on 2019-nCoV infections as at 12 January
On 9 January 2020, a novel coronavirus, 2019-nCoV, was officially identified as the cause of the outbreak of pneumonia in Wuhan. Following the official announcement of the genetic sequence of the virus, on 11 January, 41 laboratory-confirmed cases of 2019-nCov infection with pneumonia were reported in Wuhan [15]. While the case definition for laboratory-confirmed cases has not been officially published, our understanding is that the initial case definition required (i) fever, (ii) x-ray evidence of pneumonia, (iii) white blood cell count normal or low or low lymphocyte count, (iv) antibiotic treatment for 3 days without improvement, in addition to (v) one or more recent visits to Wuhan or direct or indirect exposure to a wet market in Wuhan, and (vi) a respiratory specimen positive for 2019-nCoV and confirmed as 2019-nCoV by whole genome sequencing. The earliest known case had illness onset on 8 December 2019.
Between 10 and 12 January when there were no new cases reported, the Wuhan Municipal Health Commission announced that no new cases of 2019-nCoV infection were identified with illness onset after 3 January. As at 11 January, more than 700 close contacts were under medical surveillance, more than half being healthcare workers (HCWs), with no infections being identified [15]. Among the first 41 confirmed cases, approximately 70% reported exposure to the Southern China Seafood Wholesale Market [16]. Using the method described by Cauchemez et al. [17], assuming that the market was the only source of zoonotic infections, we estimated R 0 to be 0.3 (95% confidence interval (95% CI): 0.17–0.44).