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COVID-19: some unanswered questions
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  1. Philip D Welsby
  1. Retired, Edinburgh, UK
  1. Correspondence to Dr Philip D Welsby, Retired, Edinburgh EH12 8UB, UK; philipwelsby{at}aol.com

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In 2003, severe acute respiratory syndrome (SARS) spread through 26 countries, infecting at least 8098 and causing at least 774 deaths (a case fatality rate of 9.6%). Middle East respiratory syndrome (MERS) by January 2020 caused 2519 cases and 866 deaths (a case fatality rate of 34%). SARS and MERS are coronaviruses and both are not as easily transmitted as COVID-19 because they require close contact with those infected (or also with camels in the case of MERS), and infected humans tend not to transmit before they have symptoms. Transmission of both mostly occurred within healthcare settings and could be controlled by improving infection control in hospitals.

In 2015, Bill Gates in a TED lecture warned that we were more at risk of a global pandemic (he thought it would be influenza) than we were from nuclear war.

COVID-19 probably first entered the human population in China in November 2019 in Wuhan and was first identified as such in December 2019. It spreads easily with a R0 (basic reproduction number) that represents the average number of people the average infected person would infect being between 1.5 and 3.5, depending on the surrounding circumstances. While a large proportion of infections are asymptomatic, there is a significant mortality rate (about 3.4% worldwide). Survival rates are worse in the elderly, in men and in those with comorbidities. There are no suitable mammal models to study.

Because there is a significant proportion of asymptomatic infectious people, monitoring of epidemics necessitates screening to determine (1) the proportion of the population that is actively infected and or (2) the total number of those who have been infected. Both require screening. To gain significant data, then whole populations or representative samples have to be tested. In many circumstances, only those with high probability are tested.

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