On case-fatality rate: review and hypothesis.
The relationship between log cumulative number of patients (X) and that of deaths (Y)  in an epidemic follows the equation logY = klogX - klogN(0), where k is a constant determining the slope  and N(0) is the value of X when Y = 1. Diseases with k = 1 are Ebola hemorrhagic fever, avian influenza H5N1,  cholera, and hand, foot, and mouth disease; those with k > 1 are the influenza H1N1 2009 pandemic in countries  other than Mexico and the SARS epidemic in some countries; and those with k < 1 include the influenza H1N1 2009  pandemic in Mexico. Epidemics with k > 1 can be simulated by postulating two subpopulations (normal population [NP]  and vulnerable population [VP]), where the epidemic proceeds at higher speed and at higher mortality in VP than  in NP. Epidemics with k < 1 can be simulated by postulating coexisting high virulence virus (HVV) and  low virulence virus (LVV), with the former being propagated at slower speed and with a higher mortality rate than  the latter. An epidemic with k > 1 was simulated using parameters that are fractions of subpopulations NP or VP  from the total population (f) and NP- or VP-specific patient multiplication (M) and mortality (D) rates. An  epidemic with k < 1 was simulated using parameters that are fractions of HVV- or LVV-infected human  populations (f), and HVV- or LVV-specific M and D.
National Institute of Infectious Diseases, Tokyo, Japan. yoshikura-hiroshi@mhlw.go.jp
Hiroshi
H
Yoshikura
D058872:Epidemics; D006801:Humans; D007251:Influenza, Human / Q000453:epidemiology; D008800:Mexico / Q000453:epidemiology; D015233:Models, Statistical; D045169:Severe Acute Respiratory Syndrome / Q000453:epidemiology; D013997:Time Factors; D014777:Virus Diseases / Q000453:epidemiology / Q000401:mortality*