3.3 Syndromic surveillance
Syndromic surveillance can be passive or active and involves gathering routinely collected data on signs, symptoms or clinical diagnoses of disease in human or animal health, when laboratory confirmation of disease is either unavailable or not timely. This methodology is employed in situations where an early warning system is needed, including to identify emerging syndromes and diseases; for example, it can be set up in busy Emergency Departments in hospitals across a country to rapidly detect spikes in seasonal influenza, based on number of people presenting to the Department with symptoms suggestive of possible influenza (for example, report of fever or measured high temperature). Information gleaned from this form of surveillance serves as an early warning flag for the health system, allowing for prompt interventions to mitigate disease spread and adjust health service capacity.
Syndromic surveillance also triggered the alarm bell which later led to the identification of BSE, when the number of neurological syndromes in cattle surged above the ‘usual’ incidence. This methodology is often cheap to implement, in part due to its lack of dependability on laboratory confirmation processes. The focus on signs and symptom data does make systems employing this methodology less accurate for pinpointing the cause of disease. For example, a ‘rash’ could be a sign of anything from dermatitis (i.e. skin inflammation) to a haemorrhagic fever (a rare but life-threatening condition), so this might be a poor choice of a syndromic indicator. Giving more specific details, such as a description of the rash, may improve specificity.
Example: Acute flaccid paralysis (AFP) is a complex clinical syndrome characterised by rapid onset of weakness and difficulty in breathing and swallowing, among other symptoms. Signs and symptoms of AFP are a key red flag in diagnosing polio. In Ireland, since 2012, all clinicians working in health facilities (hospitals, community practices) are requested to report when a child has a diagnosis of AFP to the Health Protection Surveillance Centre (HPSC). This report is used to trigger an immediate investigation by the HPSC to understand if the AFP symptoms are linked to polio disease. This has proved the best manner of surveillance – as in the early stages of the polio, the symptoms of AFP mirror those exhibited by other diseases and because polio is extremely rare in Ireland, clinicians may not immediately consider or investigate for polio. This delay might result in more people being exposed to the disease. To ensure no case of polio goes undetected and to ensure that investigations start as soon as possible, polio surveillance targets the symptom rather than the disease. Similar forms of AFP syndromic surveillance is part of a global effort to eradicate polio and is spearheaded by the World Health Organisation (WHO). If you have time, read more about acute flaccid paralysis surveillance [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] (HPSC, 2019).
