Comparing data in different time periods
In order to assess your progress in preventing communicable diseases and other disorders in your community, it is essential to compare the incidence rate (explained above) of each condition at different times (e.g. in the present year compared to the previous year).
Suppose that the incidence rate of typhoid in a community was 10 per 1,000 population in 2009, whereas in 2010 it was 50 per 1,000 population. How has the incidence of typhoid in this community changed?
The incidence of typhoid has increased sharply – it was five times higher in 2010 than it was in 2009, having increased to 50 per 1,000 population from 10 per 1,000.
When the incidence of a disease has increased compared to the previous figure, it may indicate an epidemic, so you should immediately report it to the Health Centre and/or District Health Office. It is also important to describe the distribution of cases by age, sex and place of residence. You will learn more about epidemic surveillance and reporting in Study Sessions 41 and 42.