Epidemiology of SARS-CoV-2 infection and COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a new beta-Coronavirus that was first detected in 2019 in Wuhan, China. In the ensuing months it has been transmitted worldwide. Here the authors present the current knowledge on the epidemiology of this virus. SARS-CoV-2 replicates mainly in the upper and lower respiratory tract and is primarily transmitted by droplets from asymptomatic and symptomatic infected subjects. The estimate for the basic reproduction number (R) is currently between 2 and 3, while the incubation period is 6 (median, range 2-14) days. Although most infections are uncomplicated, 5-10% of cases develop pneumonia, which can lead to hospitalization, respiratory failure and multiorgan failure. Risk factors for a complicated disease course include age, hypertension, chronic cardiovascular and pulmonary disease and immunodeficiency. The overall case fatality rate is 1.4%, with the rate rising in the sixth decade of life. Nosocomial and infections in medical personnel have been reported. Drastic reductions in social contact have been implemented in many countries with outbreaks of SARS-CoV-2, leading to rapid reductions in R. Which of the measures have been effective is still unknown.