2.2.1. Passive surveillance

This is the type of survey where beekeepers voluntarily send in suspect bee samples to a diagnostic laboratory for analysis. Most countries operate such a service and often the samples are of colonies that died suddenly, usually after winter. The survey is ‘passive’ since it only analyses material received from the public. It is analogous in human epidemiology to the entry reports of health care facilities for active disease cases. There is no statistically designed sampling strategy, samples will be biased by beekeeper interest, experience and knowledge and proximity to the diagnostic facilities. Samples will arrive in various states of decomposition making definitive diagnosis problematic (see section 4; ‘Virus Sample Management’), the data will be heavily biased towards diseased colonies with high pathogen prevalence/titre and the results will be more relevant to the management of epidemics rather than to their prevention.