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

January 1994 – March 2005

N J Andrews, Senior Statistician

Statistics Unit, CDSC, Health Protection Agency

14th April 2005

Summary | Introduction | vCJD data | Methods | Results

Summary

Two new cases of vCJD were diagnosed from January to March 2005, bringing the total reported in the UK to 155.   Of these cases, 149 have died, including one in the last quarter.  Six 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 1.5 deaths per quarter.  Extrapolating the best fitting model (the quadratic model) gives an estimate of 5 deaths in the next 12 months (95% prediction interval 1 to 11). 

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 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 March 2005.  Since the previous report, which covered the period to the end of December 2004, two further cases of vCJD have been diagnosed giving a total of 155 cases.  There have now been a total of 149 deaths reported, with one in the most recent quarter. 

vCJD data

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  March 2005 (Table 1).

Table 1    Cases of vCJD classified as definite or probable by end of March 2005

*Deaths including 107 definite and 42 probable (without neuropathological 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 as 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=0.15).

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)

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 (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=0.68).  The plateau model did not fit the data as well as the quadratic model with 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 1.5 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 5 deaths in the next 12 months with a 95% prediction interval of 1 to 11.  

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