1.3.1. Point prevalence
Point prevalence is the frequency of ongoing disease in a defined population at a certain point in time (Equation 1.3.1).
The method for calculating the 95% confidence interval for point prevalence is outlined in section 18.104.22.168. Again, it is important to stress that calculating the CI assumes the sample pool is representative of the population as a whole, this is best achieved if the sample was randomly drawn from the population. The estimate of the point prevalence is affected by the likelihood that a disease will be detected during a given inspection. Diseases which occur for only short periods of time are less likely to be observed during an inspection than are diseases that are more chronic (Box 2).
In the summer of 2006 apiary inspectors in Pennsylvania inspected a sub-set of beekeeping operations in the state. In total, 1,706 apiaries were inspected containing 11,285 colonies. Clinical signs of Chalkbrood (CB) disease were found in a total of 384 colonies located in 156 apiaries (vanEngelsdorp, unpublished data).
Thus, assuming that the inspected apiaries were representative of the entire Pennsylvanian population, Chalkbrood was present in 9% of all apiaries (95% CI: 7.6 - 10.4%) while 3.4% (95% CI 3.1 – 3.7%) of all colonies had clinical signs of the disease.