Cholera can spread very easily from person to person, because even a few bacteria are enough to cause the disease if the person is already vulnerable, e.g. due to malnutrition or other infections. Although about 75% of people infected with the bacteria do not develop any symptoms, they can still pass on the infection in their faeces for up to two weeks, so epidemics can develop very quickly.
Do you remember the definition of an epidemic? (Think back to Study Session 1 in Part 1 of this Module.)
An epidemic is defined as a sudden rise in the number of cases of a condition, which go on increasing for weeks or months before being brought under control; sometimes the numbers affected in an epidemic can continue rising for years (e.g. HIV/AIDS).
There have been epidemics of cholera in Ethiopia; in 1970, several thousand deaths occurred in the eastern, central and southern regions of the country. Conditions leading to epidemics include the consumption of unsafe water, poor hygiene, poor sanitation and crowded living conditions. Cholera often follows after natural disasters involving flooding, and when large numbers of refugees live in camps (Figure 33.2). Consideration of these factors is important for the prevention and control of epidemics of cholera. In Section 35.2 of this study session, we mention the actions that should be taken to prevent a single case from leading to an epidemic. The details of epidemic investigations and management more generally are the subject of Study Session 42.