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How is COVID-19 transmitted and why so many cases are there?

It was initially suggested that the patients of Wuhan China infected by coronavirus (COVID-19) visited the seafood market where they sell live animals and are eaten as a source of food.  However, later investigation revealed that some people were infected even without registering a visit to this market.1

These observations indicate that the human being has the ability or spreading (transmitting) this virus to another human being and that the means of spreading can be possible in viral transference that an animal acts as intermediary host (a living organism that has the disease and that can transmit it and can sicken a human being), although this has not been proven.1


Transmission from human being to human being is produced by close contact with an infected person, by exposure to cough, sneezing, breathing droplets or aerosol.  These aerosols can penetrate into the human body through inhalation by mouth or nose.2


The causes of the rise in cases can be explained by:

  • The virus’ transmission capacity, which represents the average number of new infections generated by an infected person.2
  • The incubation period, which the time between initial exposure and the appearance of symptoms, which explains the high amount of infections.2
  • The series interval, which is the time between the transmission of the disease between an initial case and a case where such exposure hadn’t taken place. The increase of this factor indicates an increase in transmission cases before the beginning of the disease.2

All these factors can explain the increase of cases of the disease.

  1. Shereen MA, Khan S, Kazmi A, Bashir N, Siddique R. COVID-19 infection: Origin, transmission, and characteristics of human coronaviruses. Journal of Advanced Research 2020;24:91–8. doi:10.1016/j.jare.2020.03.005.
  2. Xie M, Chen Q. Insight into 2019 novel coronavirus — an updated intrim review and lessons from SARS-CoV and MERS-CoV. International Journal of Infectious Diseases 2020. doi:10.1016/j.ijid.2020.03.071.