Current cholera outbreaks in Haiti and Pakistan emphasise the importance of a seemingly simple task: counting. How many people have suffered and died from cholera in these countries? Based on these numbers public health officials make decisions about how best to use limited resources to fight these outbreaks. In the case of cholera, this could be to introduce a cholera vaccine which costs as little as $3.70 per person, providing clean drinking water or filtration systems since cholera is typically transmitted through consuming contaminated water and food.
The official statistics for these emerging outbreaks report the number of confirmed cases. A case is confirmed when the bacterium that causes cholera is isolated from a patient showing cholera symptoms. This means a sample from that individual needs to be collected, this sample needs to be sent to a lab, and the lab needs to analyse the sample for this particular bacterium. There are a lot of steps in this process that could slow down the collection of a sample in the first place. Therefore confirmed cases are a lower limit for the number of actual cases and is therefore an undercounting of the actual number of cases.
One approach to solving this problem is to make sure that everybody who is showing cholera symptoms has a sample taken and analysed by a lab. Unfortunately there are just not enough public health officials nor laboratories to handle every sample that this would generate.
An alternative approach is to understand the under-reporting bias by sampling the population. The idea is to randomly choose a relatively small number of individuals and determine how many of these individuals have cholera and how many of these cases have been confirmed through the traditional route. The ratio of cholera cases to confirmed cases then allows an estimation of the total population who have cholera. One estimate of this ratio is 4:1 which would make the number of cholera cases greater than 30,000.
Now that cholera has reached Haiti's over-crowded capital of Port-au-Prince, the need for effective public health response is even more pressing. But public health officials cannot do their job properly unless they have accurate data concerning the number of people affected.