Читать книгу Principles of Virology, Volume 2 - Jane Flint, S. Jane Flint - Страница 38

Three other measures used in epidemiology can cause confusion because of the similarity of their definitions: mortality, morbidity, and case fatality ratios (Box 1.5). The mortality rate is expressed as a percentage of deaths in a known population of infected individuals normalized to the whole population in a period of time. The morbidity rate is similar but refers to the number of infected individuals in a given population who show symptoms of infection. The morbidity percentage will always be higher than the mortality percentage, of course, because not all sick individuals will die of the infection.

In contrast, a case fatality ratio is a measure of the number of deaths among clinical cases of the disease, expressed as a percentage. As an example, if 200 people are diagnosed with a respiratory tract infection and 16 of them die, the case fatality ratio would be 16/200, or 8%. In a technical sense, the use of the word “ratio” is incorrect; a case fatality ratio is more a measure of relative risk than a comparison between two numbers.