Technical supplement - COVID-19 Australia: Epidemiology reporting Last updated 19 January 2021.

Summary: This supplement to the series of regular Australian coronavirus disease 2019 (COVID-19) epidemiological reports describes the technical background to the surveillance data reported through Communicable Diseases Network Australia (CDNA) as part of the nationally-coordinated response to COVID-19. Background: Coronavirus disease 19 (COVID-19), caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was first identified in humans in Wuhan, China, in December 2019. The disease subsequently spread rapidly, leading to a global pandemic.1 The predominant modes of transmission for COVID-19 are through direct or close contact with an infected person via respiratory droplets, or indirectly via contact with contaminated fomites.2 The median incubation period of COVID-19 is 5-6 days, ranging from 1 to 14 days.3,4 The infectious period remains uncertain; however, it is estimated to be from 48 hours before symptoms develop until two weeks after symptom onset.3,5 The predominant symptoms reported in COVID-19 cases are cough, sore throat, fatigue, runny nose and fever.6 The majority of cases recover from the disease without clinical intervention; however, approximately 20% of global cases result in more severe outcomes, such as shortness of breath and pneumonia, necessitating hospitalisation and the requirement of additional oxygen or ventilation.7,8 Severe or fatal outcomes are generally more common among elderly cases or those with comorbid conditions.8 A visual depiction of the severity spectrum of COVID-19, and of the data sources that we use in this report to measure aspects of severity, is provided in Figure 1. © Commonwealth of Australia CC BY-NC-ND.