INCIDENCE OF VARIANT CREUTZFELDT-JAKOB DISEASE ONSETS AND DEATHS IN THE UK

January 1994 – September 2004

N J Andrews, Senior Statistician

Statistics Unit, CDSC, Health Protection Agency

7 October 2004

Summary | Introduction | Background Information | Methods | Results

Summary

Two new cases of vCJD was diagnosed from July to September 2004, bringing the total reported in the UK to 149.  Of these cases, 144 have died, including two in the last quarter.  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 about 2 deaths per quarter.  Extrapolating the best fitting model (the quadratic model) gives an estimate of 6 deaths in the next 12 months (95% prediction interval 1 to 12).

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.

Introduction

Each quarter 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 disease onsets and 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 September 2004.  Since the previous report, which covered the period to the end of June  2004, two further cases of vCJD have been diagnosed giving a total of 149 cases. There have now been a total of 144 deaths reported, with two in the most recent quarter.

Background Information

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 as probable or, when this is not available, the date of confirmation of a definite case.

For these analyses we have included all cases notified to the NCJDSU and classified as definite or probable by the end of  September 2004 (Table 1).

Table 1    Cases of vCJD classified as definite or probable by end of  September 2004

*Deaths including 104 definite, 38 probable (without neuropathological confirmation) and 2 awaiting confirmation.

There have been more deaths in males than females (56% males) but this excess is compatible with random variation (p=0.14).

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	3	15	16	18	28
2004-Q3	2	3	4	5	33
Total	149	149	149	144	28

 

Methods

After grouping deaths by quarter the 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.

 

Results

The quadratic trend model fits the data better than the exponential model (p<0.001) (see figure).

 

 

There was no evidence that the cubic model is an improvement on the quadratic model (p=0.47).  The plateau model did not fit the data as well as the quadratic model with significant evidence of a lack of fit (p=0.01), indicating that a peak has been passed.

From the quadratic model the current incidence is estimated at 2 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 6 deaths in the next 12 months with a 95% prediction interval of 1 to 12.

 

 

Click here to return to Home Page