A carrier is a person who is infected with an organism but shows no evidence of disease, although disease may have been present earlier. Chronic infection refers to a 'long-standing' condition during which the pathogen continually replicates and the patient may be persistently infectious to others, e.g., hepatitis B infection. Latent infection refers to a persistent infection with the possibility of intermittent shedding of pathogens, e.g., varicella zoster virus causing shingles or herpes simplex virus causing cold sores or genital herpes. Infection in Populations Endemic infection refers to infection or disease that occurs regularly at low or moderate frequency. Epidemics occur when there are sudden increases in frequency above endemic levels.
Pandemics are global epidemics.
The size of 'outbreaks is dependant upon factors such as the ratio of susceptible to immune subjects, period of infectivity, population density, etc. The prevalence of infection describes the number of acses in a population at a point in time, whereas the incidence refers to the number of cases arising over a defined period of time. Secular trend refers to a change in the prevalence of infection over years. This relates to better living conditions, better hygiene, and vaccination. An example of a secular trend is the decrease in tuberculosis in the United Kingdom.