In
epidemiology, an
outbreak is a sudden increase in occurrences of a
disease in a particular time and place. It may affect a small and localized group or impact upon thousands of people across an entire continent. Two linked cases of a rare
infectious disease may be sufficient to constitute an outbreak. Outbreaks may also refer to
epidemics, which affect a region in a country or a group of countries, or
pandemics, which describe global disease outbreaks.