What have we learned from the investigations of the first known human COVID-19 cases?
As soon as the first cases of COVID-19 were reported in late December 2019, investigations were conducted to understand the epidemiology of COVID-19 and the original source of the outbreak.
- A large proportion of the initial cases in late December 2019 and early January 2020 had a direct link to the Huanan Wholesale Seafood Market in Wuhan City, where seafood, wild, and farmed animal species were sold.
- Many of the initial patients were either stall owners, market employees, or regular visitors to this market.
- Environmental samples taken from this market in December 2019 tested positive suggesting that the market in Wuhan City was the source of this outbreak or played a role in the initial amplification of the outbreak.
The market was closed on 1 January 2020 and was cleaned and disinfected.
- The virus could have been introduced into the human population from an animal source in the market or an infected human could have introduced the virus to the market and the virus may have then been amplified in the market environment.
- Subsequent investigations into the first human cases have determined that they had onset of symptoms around 1 December 2019.
- However, these cases had no direct link to the Huanan Wholesale Seafood Market and they may therefore have been infected in November through contact with earlier undetected cases (incubation time between date of exposure and date of symptom onset can be up to 14 days).
- Additional studies are ongoing to as whether unrecognized infections in humans may have happened as early as mid-November 2019.
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