This article documents the chronology and epidemiology of SARS-CoV-2 in 2019, the virus that causes coronavirus disease 2019 (COVID-19) and is responsible for the COVID-19 pandemic. The first human cases of COVID-19 known to have been identified were in Wuhan, Hubei, China, in December 2019. It marked the beginning of the 2019–2020 COVID-19 outbreak in mainland China.
Unconfirmed reports of early cases
A September 2020 review noted the hypothetical possibility that the COVID-19 infection had already spread to Europe in 2019 by presumptive evidences including pneumonia case numbers and radiology in France and Italy in November and December. However, a subsequent retrospective surveillance report determined there was no evidence of SARS-CoV-2 circulation in Rome (Italy) during this period.
Some medical and environmental analyses in Italy, France, and the US found results which suggested the virus was circulating prior to December 2019 by several weeks. A WHO report states: "the study findings were not confirmed, methods used were not standardized, and serological assays may suffer from non-specific signals". It urges further investigation of these potential early events.
October and November
According to an ABC news report, the American National Center for Medical Intelligence shared intelligence in late November, based on analysis of wire and computer intercepts and satellite images, regarding a potential respiratory disease in Wuhan. This was denied by the Pentagon. On 13 March 2020, the South China Morning Post reported that Chinese government records suggest that the first case of infection with COVID-19 could be traced back to a 55-year-old Hubei resident on 17 November.
On 23 May 2021, The Wall Street Journal reported that newly disclosed U.S. intelligence obtained that three researchers working at the BSL-4 laboratory of the Wuhan Institute of Virology were hospitalized with COVID-like symptoms. The report added weight to calls for a broader probe into the theory that the COVID-19 virus could have escaped from a laboratory. However, a WHO report states "introduction through a laboratory incident was considered to be an extremely unlikely pathway". Since then, the head of the WHO COVID-19 origins investigative team, Peter Ben Embarek, has stated that the Chinese authorities exerted pressure on the WHO report conclusions, and that he in fact considers an infection via a researcher's field samples to be a "likely" scenario.
1 December
Symptoms of the index case, or patient zero, began on 1 December. The man had not been to the Huanan Seafood Wholesale Market. His family was unaffected, and no epidemiological link was found between him and the other laboratory-confirmed cases as of 2 January.
8 December
First hospitalizations
This was the onset of the first 41 people who were tested and later confirmed positive for COVID-19, as reported by the Wuhan City Health Committee and the WHO in 2020.
10 December
Symptoms of three more cases began on 10 December, which were later confirmed by laboratories. These patients are known because they became hospitalized on 16 December and thus sampled. Their results were confirmed two of these three had no direct exposure to the Huanan Seafood Wholesale Market, while the other did.
15 December
The fifth and sixth cases that were later confirmed by laboratories first felt symptoms on 15 December. Both patients had direct exposure to the Huanan Market.
16 December
, the first documented COVID-19 hospital admissions worldwide were dated to 16 December 2019 in Wuhan.
24 December
An unresolved clinical case sparks off the first scientific involvement: a bronchoalveolar lavage fluid (BAL) sample was sent from Wuhan Central Hospital to Vision Medicals (广州微远基因科技) in Guangzhou, a private company specializing in metagenomic massive parallel sequencing analysis. According to the GenBank record, the sample was obtained 23 December, whereas sets the date to 24 December 2019.
27 December
First novel disease report
According to news reports in February 2020—Workers Daily, Global Times—at the Hubei Provincial Hospital of Integrated Chinese and Western Medicine and following the report from Doctor Zhang Jixian, the hospital immediately alerted the local CDC, Wuhan Jianghan Disease Prevention and Control Center, however, the report of 22 January 2020 from the Chinese CDC seems to claim this contact falling on 29 December.