Page 91 - Timeliness of Infectious Disease Notification & Response Systems - Corien Swaan

Quantifying reporting timeliness to improve outbreak control 89
Introduction
Timely reporting of infectious diseases cases enables public health authorities (PHAs) to take effective action to prevent outbreaks by reducing disease trans- mission in the population. Therefore, many countries have notification systems for reporting infectious diseases to local PHAs. However, delays in the chain of reporting are inevitable. Fig. 1 shows a schematic notification delay chain with its various delay links. The cause and duration of these links have diverse origins that must be individually analyzed to find possible ways of reducing them but only if reducing the total reporting delay (DOR in Fig. 1) proves worthwhile. Alt- hough any reduction of reporting delay provides individual benefit, aiming for overall reduction of the reporting delay makes sense at population level only if a given goal for improving outbreak control can be achieved. Therefore, the question arises as to whether PHAs should spend time, money and efforts to achieve effective improvement of the total reporting delay.
Previous studies have found that for most diseases, the reporting delays are too long to prevent directly infected contacts from spreading the disease (1–3). Few studies have taken into account the full-time distribution in time of events in the reporting chain (4,5) and there has been no quantitative assess- ment of the effect of reporting delays on outbreak control. Moreover, assessing reporting timeliness by considering only time delay does not enable a compa- rison among different diseases because they generally develop over different timescales.
In this manuscript, we show how to quantify reporting timeliness for out- break control by calculating the proportion of infections expected to be caused by index cases and by their corresponding secondary cases (6), until the mo- ment the index case is reported to a PHA. This approach enables not only quan- titative assessment of the effect of reporting delay reduction for a particular disease, but also comparison of reporting timeliness among different diseases. Our models take into account reporting delay distributions, generation (serial) interval distributions, and distributions of symptom-onset period. We used no- tification data of 6 infectious diseases reported to the Netherlands notification system to evaluate the current reporting timeliness and reporting delay reduc- tions needed to substantially affect outbreak control. The effect of a reporting delay on new infections acquired from an index case (and subsequent seconda- ry cases) indicates to public health officials the potential value of attempting to reduce the total reporting delay and the extent to which it may need to be done.
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