Volume 14, Number 10—October 2008
Dispatch
Automatic Outbreak Detection Algorithm versus Electronic Reporting System
, Doris Altmann, Tim Eckmanns, and Gérard Krause
Table
Outbreaks January 31, 2005–January 28, 2007, reported and identified by detection algorithm*
| Outbreak characteristic | Campylobacter spp., no. (%) | Norovirus, no. (%) |
|---|---|---|
| Total cases | 114,176 | 144,568 |
| Cases as part of a reported outbreak | 3,767 (3.3) | 103,177 (71.4) |
| Reported outbreaks with <4 cases | 1,453 | 5,074 |
| Reported outbreaks with >4 cases | 118 | 4,309† |
| Signal outbreaks generated by detection algorithm |
781 |
2,801 |
| Reported outbreaks with >4 cases identified by detection algorithm signals | 52 (100) | 2,538 (100) |
| Reported outbreaks identified by 1 signal | 49 (94.0) | 1,811 (71.4) |
| Reported outbreaks identified by >1 signal | 3 (6.0) | 727 (28.6) |
| Reported outbreaks identified by 2 signals‡ | 3 (6.0) | 473 (18.6) |
| Reported outbreaks identified by >2 signals‡ |
0 |
254 (10.0) |
| Signal outbreaks corresponding to reported outbreak with >4 cases | 50 (100) | 2,115 (100) |
| Signal outbreaks corresponding to 1 reported outbreak | 46 (92.0) | 1,355 (64.1) |
| Signal outbreaks corresponding to >1 reported outbreak | 4 (8.0) | 760 (35.9) |
| Signal outbreaks corresponding to 2 reported outbreaks§ | 3 (6.0) | 408 (19.3) |
| Signal outbreaks corresponding to >2 reported outbreaks§ | 1 (2.0) | 352 (16.7) |
*Data through June 1, 2007. Sensitivity detection algorithm 44.1% (52/118) for Campylobacter spp., 58.9% (2,538/4,309) for norovirus; no. reported outbreaks with >4 cases also identified by detection algorithm signal/total no. reported outbreaks with >4 cases. Positive predictive value of detection algorithm 6.4% (50/781) for Campylobacter spp., 75.5 (2,115/2,801) for norovirus. No. signal outbreaks identical to reported outbreak/total number of signal outbreaks.
†Excluded are 17 reported norovirus outbreaks of >25 wk and an average of <2 cases/wk because these are likely the result of data entry errors in SurvNet.
‡During the duration of a reported outbreak, the detection algorithm may have triggered multiple signals during several consecutive weeks (Figure 1).
§One signal outbreak may correspond to multiple reported outbreaks if different outbreaks occur in the same municipality during the same period (Figure 2).