Epidemics begin in one of three model independent ways.
- Exponential (Incidence accelerates rapidly)
- 1918 Influenza (San Francisco, 1918)
- Plague (Bombay, 1905)
- Smallpox (Khuina, Iran, 1977)
- Power (Incidence increases day by day)
- Measles (London, 1948)
- HIV/AIDS (New York City, 1982 – 2002)
- Linear (Incidence remains constant)
- Heart Disease
COVID-19 in New York City illustrates one such pattern. Tab through and see for yourself.
The first 5 days were unremarkable to many - only a few cases.
Perhaps 4 more cases each day than the day before.
The epidemiologists at the Public Health Department saw a very different progression of cases - an exponential growth of cases.
Day six brought more cases than expected from a simple linear growth pattern.
Perhaps a growth according to a power function (a quadratic equation)?
Perhaps an exponential growth?
Yes - an exponential !
New cases on day seven were definitely on the exponential curve!!
! ! Plague ! !
Remarkably - the first 5 days predicted the course of the COVID-19 epidemic over the next two weeks.
The Mayor was convinced, and within days the Governor was too. The city closed down!
The next month did slow the epidemic to a linear growth pattern - averaging 4,600 new cases a day!
Finally, a pause after two months.