INCIDENCE
OF VARIANT CREUTZFELDT-JAKOB DISEASE DEATHS
January 1994 – June 2006
N J Andrews, Senior Statistician
Statistics Unit
18 July 2006
Summary | Introduction | vCJD data | Methods | Results
Two new cases of vCJD were diagnosed from January to June 2006, bringing the total number of cases reported in the UK to 161. Of these cases, 156 have died, including 3 in the last 6 months. Five diagnosed cases are still alive.
Results from modelling the underlying incidence of deaths indicate that the epidemic reached a peak at about 6 deaths per quarter in mid 2000 and has since declined to a current incidence of under one death per quarter. Extrapolating the best fitting model (the quadratic model) gives an estimate of one or 2 deaths in the next 12 months (95% prediction interval 0 to 3), however with 5 cases currently alive a prediction of one or 2 deaths is likely to be a slight underestimate.
It is important to note that although a peak has been passed, it is possible that there will be future peaks, possibly in other genetic groups. There is also the possibility of ongoing person to person spread.
Each quarter (now every 2 quarters) data on diagnosed cases of variant Creutzfeldt-Jakob disease (vCJD) in the UK are reviewed in order to investigate trends in the underlying rate at which deaths are occurring. The present report reviews the data for all individuals who had been classified as definite or probable cases by the end of June 2006. Since the previous report, which covered the period to the end of December 2005, 2 further cases of vCJD have been diagnosed giving a total of 161 cases. There have now been a total of 156 deaths reported with 3 in the last 6 months.
For these analyses we have included all cases notified to the National CJD Surveillance Unit (NCJDSU) and classified as definite or probable by the end of June 2006 (Table 1).
Table 1 Cases of vCJD classified as definite or probable by end of June 2006
| Dead* | Alive | Total | |
| Male | 88 | 2 | 90 |
| Female | 68 | 3 | 71 |
| Total | 156 | 5 | 161 |
*Deaths including 111 definite, 44 probable (without neuropathological confirmation) and one case awaiting confirmation.
Definite cases are those confirmed neuropathologically. To date all probable cases for which neuropathological data have become available have subsequently been confirmed as definite. The date of diagnosis is taken as the date when diagnosed probable or, when this is not available, the date of confirmation of a definite case. There have been more deaths in males than females (56% males) but this excess is compatible with random variation (p=0.13).
Numbers of cases by onset, notification, diagnosis and death are given below by year along with the median age at death by year of death (Table 2).
Table 2 Annual cases by onset, notification, diagnosis and death (including median age at death by year of death)
|
Year |
Onset |
Notified |
Diagnosis |
Death |
Median age at death |
|
1994 |
8 |
0 |
0 |
0 |
- |
|
1995 |
10 |
8 |
7 |
3 |
- |
|
1996 |
11 |
9 |
8 |
10 |
30 |
|
1997 |
14 |
13 |
12 |
10 |
26 |
|
1998 |
17 |
20 |
17 |
18 |
25.5 |
|
1999 |
29 |
16 |
17 |
15 |
29 |
|
2000 |
24 |
29 |
27 |
28 |
25.5 |
|
2001 |
17 |
21 |
25 |
20 |
28 |
| 2002 |
14 |
15 |
16 |
17 |
29 |
| 2003 | 5 | 16 | 16 | 18 |
28 |
| 2004 | 9 | 6 | 8 | 9 |
26 |
| 2005 | 3 | 7 | 6 | 5 |
34 |
| 2006 | 0 | 1 | 2 | 3 |
30 |
| Total | 161 | 161 | 161 | 156 |
28.5 |
The median delay from onset to diagnosis is 11 months and onset to death is 13.5 months.
After grouping deaths by quarter the underlying incidence of deaths were modelled by Poisson regression using polynomials (exponential, quadratic-exponential, cubic-exponential) and also a model with a rise to a plateau. Most deaths are reported quickly so an adjustment for reporting delay is not necessary.
The quadratic trend model (figure) fits the data better than the exponential model (p<0.001). There was no evidence that the cubic model is an improvement on the quadratic model (p=0.40). The plateau model did not fit the data as well as the quadratic model (figure), indicating that a peak has been passed.
From the quadratic model the current incidence is estimated at 0.6 deaths per quarter. If the quadratic model is assumed to be correct, then the peak is estimated to have occurred in mid 2000.
Prediction for deaths in the next 12 months
The model with the quadratic term predicts a total of 1.4 deaths in the next 12 months with a 95% prediction interval of 0 to 3. Note that 5 cases are currently alive so a prediction of one or 2 deaths in the next 12 months is likely to be an under-estimate.