It is possible to estimate the effects of a particular disease in a certain population. Records are kept on an international scale by WHO (the World Health Organisation), as well as on a national scale (mainly by those economically developed countries that have sufficient resources for data collection). Outbreaks of disease that rise above a set base-level are termed 'epidemics'. A 'pandemic' is a worldwide epidemic.
The UK Public Health Laboratory keeps records in order to identify potential outbreaks of infectious diseases, especially of influenza strains. When the consultation level for influenza reaches 400/100,000 people per week in a sample of GPs’ surgeries it is said to be at epidemic levels.
In the United States, the epidemic threshold is when 7 percent of the population is infected, although this figure varies seasonally (higher in winter) and between age groups (those over 65 are more vulnerable).
There have been three influenza pandemics: 1918-19 (Spanish flu), 1957-58 (Asian flu) and 1968 (Hong Kong flu). The next one is thought to be overdue. In 1918, 20 million people died. The WHO is making contingency plans, since a worst-case scenario would see 80 percent of a population ill, 20 percent as outpatients, 0.8 percent hospitalised and 0.016 percent dead.
The following activity shows the stages of infection level from epidemic to pandemic and the changing balance between those infected and those who have recovered from the disease. Try to identify the changes.