COVID-19 is an infectious disease caused by the SARS-CoV-2 virus (severe acute respiratory syndrome coronavirus 2), a novel coronavirus. Coronaviruses are a large family of viruses that occur in humans and animals, and it is believed that the SARS-CoV-2 virus originated in bats.
The most common symptoms of COVID-19 are fever, tiredness, and dry cough. Other symptoms may include aches and pains, nasal congestion, runny nose, sore throat and diarrhea. Roughly 80% of people with COVID-19 recover without needing special treatment. Around 1 in 6 people becomes seriously ill and develops difficulty breathing. Older people, as well as those with pre-existing medical conditions such as high blood pressure, diabetes or heart problems, are more likely to develop serious symptoms.
To date, research suggests that SARS-CoV-2 is transmitted primarily through respiratory droplets from the nose or mouth of an infected person. It is possible to contract the virus by directly inhaling these droplets, or by touching a surface where droplets have landed and then touching the eyes, nose or mouth.
https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/summary.html#background
The current COVID-19 outbreak began in the city of Wuhan, China — a transportation hub with a population of 11 million. By the end of December 2019, doctors had seen dozens of patients with a form of viral pneumonia that did not respond to treatment. By this point, estimates suggest that as many as 1,000 people were already infected.
In the first 3 weeks of January, before travel was restricted, roughly 7 million people left Wuhan. On January 20th, the first cases outside China appeared in Japan, Thailand and South Korea. On January 21st, the first U.S. case was reported in Washington State. On January 24th, the first European cases were reported in France. By the end of January, when Wuhan was placed under lockdown, outbreaks were growing in 30 cities in 26 countries.
By March 1st, Italy, Iran and South Korea were each reporting thousands of cases. On March 11th, the World Health Organization declared COVID-19 a pandemic. By March 17, all 50 U.S. states were reporting cases.
https://www.nytimes.com/interactive/2020/03/22/world/coronavirus-spread.html
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