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coronavirus-A pandemic
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On 3 April 2020, the number of cases of confirmed COVID-19 globally surpassed one million 5. COVID-19 has now been diagnosed in 184 territories, in six continents according to an online virus tracker created by the medical journal, The Lancet, and hosted by Johns Hopkins University 5,13. As of 7 April 2020, there are 17 countries with >10,000 confirmed cases and 44 countries with between 1000 and 10 ,000 confirmed cases 5.
NB: Surveillance methods and capacity vary dramatically between countries, and there is reason to suspect that there may be a significant number of carriers in some countries not diagnosed.
The R0 (basic reproduction number) of SARS-CoV-2 has been estimated between 2.2 and 3.28 12,33, that is each infected individual, on average, causes between 2-3 new infections.
The incubation period for COVID-19 was initially calculated to be ~5 days, which was based on 10 patients only 12. An American group performed an epidemiological analysis of 181 cases, for which days of exposure and symptom onset could be estimated accurately. They calculated a median incubation period of 5.1 days, that 97.5% became symptomatic within 11.5 days (CI, 8.2 to 15.6 days) of being infected, and that extending the cohort to the 99th percentile results in almost all cases developing symptoms in 14 days after exposure to SARS-CoV-2 92.
The number of deaths from COVID-19 has been over 53,000 (3 April 2020), with a case fatality rate of 2-3% 5,93. It is speculated that the true case fatality rate is lower than this because many mild cases are not being tested, which thus skews the apparent death rate upwards 93.
A paper published by the Chinese Center for Disease Control and Prevention (CCDC) analyzed all 44,672 cases diagnosed up to 11 February 2020. Of these, ~1% were asymptomatic, and ~80% were classed as "mild" 25.
Another study looked at clinical characteristics in COVID-19 positively tested close contacts of COVID-19 patients 81. Approximately 30% of those COVID-19 positive close contacts never developed any symptoms or changes on chest CT scans. The remainder showed changes on CT, but ~20% reportedly developed symptoms during their hospital course, none of them developed severe disease 81. This suggests that a high percentage of COVID-19 carriers are asymptomatic.
In the Chinese population, 55-60%% of COVID-19 patients were male; the median age has been reported between 47 and 59 years 12,93.
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