Page 25 - Timeliness of Infectious Disease Notification & Response Systems - Corien Swaan

General introduction 23
public health surveillance system (1). Timeliness is also one of the indicators for evaluation the quality of a surveillance system (46). Timeliness of a surveillance system is firstly essential for early detection of infectious disease threats and initiating control. Delayed disease identification for example led to a secondary case of Lassa fever in Germany in 2017 due to incomplete personal protection equipment among contacts (47). Secondly, real-time surveillance facilitates monitoring the effect of outbreak control and preventive measures. Delayed patient identification hampers this process, as was experienced after the recall of contaminated salmon in the S. Thompson outbreak. Instead of a decrease in incidence, the recall first lead to a ‘catch up’ of already infected patients consult- ing their physician, masking a reduction of newly infected patients (28).
In an indicator based surveillance system (IBS), ideally, notifications of indi- vidual cases at local level are notified in time to prevent secondary and further cases. Obviously, timely notification is disease specific as infectious diseases have different incubation periods and periods of infectiousness. Furthermore, control measures vary widely, from eliminating a common food or environmental source, to post-exposure prophylaxes for individual contacts, or a group vaccination cam- paign. Timeliness of notifications is commonly evaluated according to the legal timeframe of a notification system or timeframes chosen for the evaluation, but these timeframes are usually not disease specific (37). Early exceptions are stud- ies by Jajosky et al. and Kite-Powell et al., who chose the incubation period of a disease as indicator for timeliness, and Moore et al., who choose a timeframe re- lated to the period of post-exposure prophylaxis against hepatitis A (31, 48, 49).
Indicators for evaluation of the capacity of a surveillance system are devel- oped by the WHO for its self-assessment (SPAR) and Joint External Evaluation (JEE) tools. An indicator for the surveillance capacity in the SPAR is ‘early warning function: indicator- and event based surveillance’ in which an optimum score is given when ‘the surveillance system is regularly evaluated and updated’ (19). In the JEE, the sustained capacity for surveillance is defined as ‘the performance of the surveillance system is regularly evaluated and updated at all levels in the country and has the capacity to support other countries in developing surveil- lance systems and/or contributes to regional or international surveillance net- works’. However, measurable indicators of performance, such as timeliness, are limited; in the JEE tool, a country is expected to have data on completeness and timeliness of reporting from at least 80% of its reporting units (10). Performance thresholds for timeliness, as maximum delay of notification time, or minimum percentage of notifications in time, are only mentioned at Points of Entry (airports, harbors): thresholds for timely action should be according to national standards.
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