About INoPSU

Methodology of surveillance

The principle of 'active' surveillance is that initiation for notification comes from the unit rather than the clinician. Active surveillance results in considerably higher case ascertainment than passive surveillance and minimises recall bias. The methodology varies slightly between units to suit local conditions. In principle, the surveillance unit sends a monthly report card to the 'mailing list' of paediatricians and asks them simply to indicate whether they have 'nothing to report' or to mark the number of new cases of each condition listed that they have seen in the previous month.

Cards are returned to the unit. The individual or organisation responsible for a study (the 'investigator') is notified of positive case reports and given contact details of the reporting clinician. The investigator is then responsible for obtaining clinical and epidemiological data from reporting doctors by postal questionnaire and is for collation, analysis, presentation and publication of data and feedback to the unit's secretariat. Alternative data sources may be used to validate ascertainment. In most countries data collection is anonymous, investigators using a patient code and having no direct access to information that would allow them to identify or contact patients or their families.

Some units use a reply-paid report card and in Australia e-mail reporting was introduced in 1997. Telephone and facsimile reporting is requested for some studies where a timely report is required e.g. to facilitate obtaining biological specimens. On receipt of a case notification one unit (NZPSU) sends study questionnaires directly to the notifying clinician, rather than sending the notifying doctor's details to the investigator, in an attempt to make receipt of questionnaires more timely. In 2003 the return rate of monthly cards to units ranged from 73 - 98% and of questionnaires from 47 - 100%. . Workload for most clinicians participating in national surveillance of rare diseases is low. In any single year a large proportion of the mailing list do not report a single case and hence are not required to complete a questionnaire requesting further details.