[Chronological trend of the incidence rate of Creutzfeldt-Jakob disease in Japan].
OBJECTIVE
The purpose of this study was to find whether the number of incidents of Creutzfeldt-Jakob disease has increased during the last decade in Japan.


METHODS
The chronological trend was observed by examining the data from a nationwide epidemiologic survey conducted by a special committee sponsored by the Ministry of Health and Welfare of Japan in May 1996. The subjects of the survey were patients with Creutzfeldt-Jakob disease who had been diagnosed between January 1985 and May 1996. Although the number of patients reported each year increased continually during the 11-year 5-month period, there were two issues that remained to cast doubt on the accuracy of this apparently obvious chronological trend: (1) the existence of hospitals that did not respond to the survey, and (2) the existence of hospitals where no information was available before a specific time during the observation period. To make up for the incomplete data, the following two methods were proposed: (1) for those hospitals where the precise annual incidence was not known, the average annual incidence for those years when the information was available should be used to make up for the missing data and (2) when a hospital did not have the information for certain years, it would be considered to be a nonrespondent for those years; the response rate should be calculated year-by-year; then the total number of patients should be obtained by the reported number of patients divided by the response rate. The first method underestimates the annual trend if a trend does exist. To evaluate the trend mathematically, linear regression and quadratic regression models were used, in which the independent variable was the calendar year, the dependent variable, the number of patients.


RESULTS
With either method, a trend for increases in incidence was noted. Statistical significance was obtained for the increasing trend in each model. It was found that the quadratic regression model was a better fit than the linear model.


CONCLUSIONS
The incidence of Creutzfeldt-Jakob disease in Japan has increased during the last decade.
Nakamura
Y
Y
Department of Health Science, Jichi Medical School, Tochigi, Japan. nakamuyk@jichi.ac.jp
Oki
I
I
Tanihara
S
S
Ojima
T
T
Yanagawa
H
H
D007562:Creutzfeldt-Jakob Syndrome / Q000453:epidemiology*; D006801:Humans; D015994:Incidence; D007564:Japan / Q000453:epidemiology; D012044:Regression Analysis; D013997:Time Factors