In fact, the term “patient zero” comes from a folk misinformation. In 1980, Dr. Darrow of the Centers for Disease Control and Prevention of the United States labeled a man related to multiple AIDS cases in Los Angeles as “patient O” in his investigation report (“O” is “Out-of-california” Means, it represents cases outside of California).
However, a well-known reporter mistakenly wrote “O” as “0 (zero)”. Since then, the word “patient zero” has spread, and its corresponding professional term should be “primary case” (referring to It is the first infected person to bring the infectious disease into a certain population in the epidemiological investigation of an infectious disease that has spread in a large area and is spread from person to person).
The determination of patient zero is mainly through DNA analysis. In zoonotic diseases, pathogens jump from animals to human hosts. With every jump from host animal to intermediate animal to human, the virus undergoes random mutations.
These mutations can cause changes in the structure of the virus. For example, every time a coronavirus jumps from one organism to another, a new spinous process is formed. With the formation of new spines, the arrangement of viral nucleotides has also changed. Therefore, even the same virus that jumps from bats to cats and then to humans has different nucleotide arrangements, and the more similar the arrangement, the closer the relationship between them.
Scientists can track the path of the virus jumping in all these animals based on the difference in nucleotide arrangement, and build a phylogenetic tree, so that they can determine who is the host animal, who is the intermediate animal, and who infects the virus to humans.
However, to determine patient zero, scientists also need to determine the earliest human patients infected, and compare the DNA of the virus in these human patients with the DNA of the virus in the animal closest to humans on the phylogenetic tree, screen out patient zero.
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