42.1  What is an outbreak and an epidemic?

If there is an increase in cases of a disease compared with the expected number, but it lasts for only a short time, or it occurs only in a limited area (e.g. in a few nearby households), the rise may be referred to as an outbreak. As you will remember from Study Session 1 of this Module, an epidemic is also an excess of cases compared with the number expected. However, an epidemic is more general than an outbreak, the increase in the number of cases continues far longer (possibly months or even years), and the cases are distributed across a wider area.

For example, it may be that during January to March there are normally fewer than 10 cases of tuberculosis (TB) in your kebele. If you found 30 cases of tuberculosis in a particular January, followed by 39 cases in February and 45 cases in March, then you would strongly suspect that there was an epidemic of TB in your community. You would then need to find out why TB had suddenly increased.

  • Which disease often causes epidemics during the months of June, September and October in Ethiopia? Why are these the months when these epidemics most often occur?

  • Malaria is the major vector-borne disease that causes epidemics in the months of June, September and October in Ethiopia. This is when the conditions are humid and warm enough and there are plentiful water collections for the vector mosquitoes to breed in. You learned about malaria in Study Sessions 5–12 of this Module.

Learning Outcomes for Study Session 42

42.2  Types of epidemics