Volume 16: Reference Material
3. Statistics
Incidence by clinical onset

3.5 The number of confirmed cases by date of clinical onset is the most appropriate and accurate way of showing the progress of the BSE epidemic. Compared with the date of notification to MAFF, it is not influenced so much by external factors (although even clinical onset has an observational bias that coincides with the increased regularity with which farmers inspect their cattle during the calving season). As mentioned above, the period of time between dates of clinical onset and notification to MAFF ranged from several weeks to six months (or even more in a small number of cases). A comparison of Figures 3.1 and 3.10 shows how the notification figures lagged behind those for clinical onset until 1996.

3.6 Confirmation could itself be held up by staff shortages, including sickness and holidays, and any technical problems at the processing centre (for example at the CVL, where the vast majority of cases were referred). Efforts to catch up after such slippages in data entry inevitably led to an increase in confirmations, and could even, on occasion, show a rising confirmation rate at the same time as a falling report rate - because the rate of confirmations was not linked to the dynamic of the disease. Thus contemporary figures showing cases by date of confirmation were unable to give a wholly reliable picture of the development of the epidemic. Hence the reliance on revised figures in this volume.

Figure 3.1: Cumulative number of confirmed cases of BSE by year of clinical onset, UK, to 20 March 1996

Figure 3.2: Number of confirmed cases of BSE by year of clinical onset, UK, to 20 March 1996

3.7 The highest annual incidence of BSE was in 1992, when there were 37,545 confirmed cases in the UK (see Figure 3.2). Of these 31,413 were in England, 3,846 were in Wales and 1,892 were in Scotland; Northern Ireland reported 394 confirmed cases in 1992. The number of confirmed cases to the end of 1996 was 7,426. There were 2,164 cases in 1999, and 647 in January-June 2000.

Figure 3.3: Distribution of confirmed cases of BSE in the UK, by country, and by month and year of clinical onset, to 20 March 1996

Figure 3.3: Continued

Figure 3.3: Continued

Figure 3.4: Distribution of confirmed cases of BSE in the UK by month and year of clinical onset, to 20 March 1996

Figure 3.5: Distribution of confirmed cases of BSE in England by month and year of clinical onset

Figure 3.6: Distribution of confirmed cases of BSE in Wales by month and year of clinical onset

Figure 3.7: Distribution of confirmed cases of BSE in Scotland by month and year of clinical onset

Figure 3.8: Distribution of confirmed cases of BSE in Northern Ireland by month and year of clinical onset

Figure 3.9: Number of confirmed cases of BSE by age at clinical onset, and by year of clinical onset, Great Britain