An outbreak of COVID-19 caused by a new coronavirus: what we know so far.

Information on the new virus and its impact is being updated constantly. We know that SARS‐CoV‐2 can cause severe disease, although active surveillance of contacts is required to define the milder end of the disease spectrum and to estimate the true hospitalisation and case fatality ratio. The cases reported to date suggest that most are older adults; it is currently unclear whether comorbidities reflect the age group affected or whether they are risk factors for severe disease.4, 5 Early studies using data before the institution of public health interventions in China suggest that SARS‐CoV‐2 is as transmissible as SARS coronavirus and probably more transmissible than influenza viruses.6, 7 The timing of infectiousness relative to symptom onset is a particularly important parameter with implications for public health control. While reports suggest that asymptomatic infection and transmission may result from minimally symptomatic cases, the contribution of this to transmission is not yet known.8 Careful analysis of early data suggests that the mean incubation period is 6 days, with a range of up to 14 days.9 Reports of large outbreaks, particularly associated with hospitals and closed communities, raise the possibility of “superspreading” events, a feature of previous coronavirus outbreaks.10 The importance of infection control is also reinforced by a report that 41% of cases in Wuhan were acquired nosocomially (including 40 health care workers and 17 patients).4