Epidemiological Overview of Intractable Diseases in Japan

This paper shows examples of the results of research projects of the Research Committee of Epidemiology of Intractable Diseases obtained in the fiscal years from 1988 to 1990. The frequency and distribution of patients with intractable diseases were estimated from statistics of financially subsidized patients, national patient surveys and nation-wide hospital surveys. Descriptive epidemiology of some examples of the diseases are shown. Case-control studies for six diseases have been conducted by the Research Committee in three recent years. As an example, results of a casecontrol study of 319 ulcerative colitis cases and controls are shown. Pathologists and epidemiologists are exploring the possibility of applying autopsy registration data to epidemiological studies. An analysis on Creutzfeldt-Jacob disease is shown.

The Committee was first organized in 1976 under the chairmanship of Professor Minoru Uematsu, who was succeeded by Professor Kunio Aoki in 1982.In 1988, the present committee was organized and is continuing with 10 consultants and 42 members.
The paper shows examples of the results of the research projects of the Research Committee of the Epidemiology of Intractable Diseases obtained in the fiscal years from 1988 to 1990.

Descriptive Epidemiology
The Committee has made nation-wide hospital surveys for the patients treated in one year for 43 selected intractable diseases by the end of 1990 fiscal year.These surveys clarified basic epidemiological pictures of the diseases.
The statistics from financially-subsidized patients also give us basic data on descriptive epidemiology.(1,2) The national patient survey is a sampling survey of one-day patients.The surveys give us estimations of the point prevalence of these diseases.The Vital Statistics Report gives us mortality data.A computerized database of autopsy records has been established and a summary report was published in Autopsy Annual every year.
The most frequent diseases in terms of number of cases treated under governmental subsidy was SLE, followed by Parkinson's disease, Ulcerative colitis, ITP, Behcet's disease and so on , comprising 170,000 cases in total in 1988.(Table 1) Among many studies on the epidemiology of intractable diseases, results of the studies on ulcerative colitis (UC) are shown as examples.The number of financially-aided UC patients was 18,449, or 15.2 per 100,000 population in 1988, doubled since 1984.(Table 2) The increase is mainly due to the increase in the number of patients who apply for the benefit of the subsidy.15% of male and 10% of female patients are hospitalized.The proportion of the patients hospitalized is higher for those less than 25 years old.(Fig. 1) Age-specific incidence curves based on newly treated cases with public aid in 1988 show that there is a peak at age 20-24 for male and 25-29 for female with another smaller peak from age 40s to 60s for both male and female.(Fig. 2) Age distribution of period prevalence rates (1 year) of new cases or cases continuously treated from the previous year in 1988 and 1984 were calculated.The second peak was relatively higher for females as compared with the peak in the incidence curve.(Fig. 3) The secondary peaks were higher than the primary peaks in the age-specific prevalence rates obtained from National One-day Patient Survey in 1984 and 1987.Two modal distributions of these three figures suggest that different causal factors may relate to young patients and to middle-aged patients.(Fig. 4).

Analytical Epidemiology
Case-control studies for six diseases have been conducted in recent three years.As an example, results of a case-control study of 319 patients with ulcerative colitis and controls are shown.Cases were collected at health centers when application forms for public aid of medical expenses were submitted.Controls were selected from residents who visited the health center clinics for health examination with sex-and age-matching.
First, risk factors were reviewed.Factors appearing in published papers were smoking, psychological factors, dietary factors and other factors.(Table 3) The odds ratios of continued smokers against non-smokers or non-smokers plus ex-smokers were low, while the ratios of ex-smokers against non-smokers or continued smokers were high.The odds ratios were inversely related to the amount of cigarettes (Fig. 5) Many articles in the literature show the same results as seen in our study.Other factors with high odds ratio were nervous temperament and unfavorable working conditions.We found no dietary factors in this study.(Table 4) The data were collected from 600 hospitals throughout Japan with 10 or more autopsies in a year.Annual number of cases registered is around 40,000, with 510,000 cases registered in the 15 year period from 1974 to 1988.The autopsy rate in Japan is about 5% .
The statistics of the autopsy cases do not reflect the entire picture , because of biases due to low autopsy rate and differences in physician's interest .However, the autopsy cases were morphologically confirmed and examined in detail.Therefore, the findings may be , in principle, useful for certain fields of epidemiological studies.

Figure 1
Figure 1 Proportion of hospitalezed-and out-patients by sex and age (ulcerative colitis)