3.2 Active surveillance
Active surveillance is defined by the act of prompting health facilities (or healthcare practitioners) to collect information on a key indicator (for example, disease event) by undertaking some activity that would not have otherwise taken place. Active surveillance usually requires substantially more time and resources (in contrast to passive surveillance) but captures more complete and detailed data. For this reason, it is often used in conjunction with a specific epidemiological investigation or question, such as when investigating a localised outbreak. Due to active surveillance being resource-intensive, it is used less widely for routine forms of surveillance.
Example: One of the important roles of surveillance is gathering data on how fast a known disease in spreading, which populations it affects and if this picture is evolving. The European Union (EU) carries out surveillance for bovine spongiform encephalopathy (BSE), a progressive neurological disease in cattle. Contaminated animal products such as cattle meat can transmit this condition to humans, in whom BSE presents as variant Creutzfeldt-Jakob disease (vCJD).
The EU’s active surveillance for BSE falls under its transmissible spongiform encephalopathies (TSE) surveillance operations (combined surveillance for all types of encephalopathies). Since 1998, EU member states have been carrying out yearly active surveillance, by performing additional testing on over one million cattle per year. This work provides insight into the prevalence of this disease and information on its evolution (such as populations and countries in which it is most widely spread). In contrast to passive surveillance, which involves farms notifying relevant authorities when disease is suspected, active surveillance covers testing of all cattle of at-risk age (generally this is animals > 24 months of age) and sending samples for laboratory testing. Surveillance data is mainly submitted through the EFSA TSE data reporting tool. Surveillance has demonstrated a continual decline in prevalence of BSE since 2001 in EU member states, from over 2000 detected cases of classical BSE per year in 2001–2002 to fewer than five cases per year in each of the past five years (EFSA, 2019). This information is crucial for the EU and helps it focus its efforts in eradicating BSE. If you have time, see more information about this surveillance work [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] (EFSA, 2019).
