Based on a mathematical model of human T-cell leukemia virus type I (HTLV-I) transmission, the non-vanishing condition of HTLV-I was derived, and the effect of changes in breastfeeding patterns on the prevalence of HTLV-I was evaluated. The non-vanishing condition was shown to be a>1/(1+b), where a is the probability of mother-to-child transmission and b is the probability of husband-to-wife transmission. This condition implies that if a is under 0.5, HTLV-I cannot be sustained in populations over a long term. The age-specific prevalences in 1985 were calculated under this model and the assumption of changes in breast-feeding over the period 1925-1985, based on information from many surveys on breast-feeding in Japan. The prevalence increased with age, like the prevalences observed in many populations in Japan. These findings suggest that the probability of mother-to-child transmission had been over 0.5 and was reduced by the spread of compound milk and the shorter duration of breast-feeding in recent years in Japan, and that it has resulted in a decrease in HTLV-I carriers among younger age groups. J Epidemiol, 1991 ; 1 : 1-5.
Self selection bias in mass-screening for gastric cancer was quantified using data from a group consisting of 66, 386 workers. Total observed person-year was 182, 779. Among males self selection bias was thought to exert some influence that made the incidence rate about 1. 13(all ages, 95%CI=0.65-1.97) or 1.23(over 40, 95%CI= 0.69-2.20)-fold higher and the mortality, rate about 1.22(all ages, 95%CI=0.48-3.13) or 1.42(over 40, 95%CI=0.54-3.69)-fold higher in the screening-attending group. Among females self selection bias was thought to exert some influence that made the incidence rate about 0.30(all ages and over 40, 95%CI=0.04-2.47 and 0.04-2.48)-fold lower and the mortality rate about 1.09(all ages, 95%CI=0.18-6.68) or 1.11(over 40, 95%CI=0.18-6.76)-fold higher in the screening-attending group. J Epidemiol, 1991 ; 1 : 7-10.
Three markers of hepatitis B virus (HBV) infection, HBsAg, anti-HBs and anti-HBc, were investigated in the sera from 426 factory workers of both sexes in a coastal city of Yantai in China. The investigation showed that the rate of those positive to HBsAg was 25.4% (25.9% in men and 24.6% in women), and that the rate when two sexes were combined was highest (i.e., 29.5%) at the ages of 20s followed by gradual decrease at higher ages (below 20%). The over-all HBV infection rate as calculated by those positive to any of the three markers studied was 70.4%. Comparison with rates reported in literature indicated that the rate of HBsAgpositive cases in the present study are probably among the highest values in China, whereas over-all rate of HBV infection was almost comparable to the values for other provinces. It should be added that other reports on other parts of Shandong Province describe HBsAg+ prevalence of about 6%. No explanation is currently available for the high HBsAg prevalence among the study population. J Epidemiol, 1991 ; 1 : 11-17.
A nation-wide case-control study was conducted to identify the risk factors and to give clues to the etiology of Buerger's disease. Cases were 153 male patients who were the receivers of national financial aids for the treatment of the disease and were enrolled in public health center. For each case, a control was randomly selected from the list of the examinees of health examinations in the public health center same as the case and was matched to the case by age (± 5 years old) and sex. Self-administered questionnaires were mailed to all study participants. The results of statistical analyses under the condition that the estimated onset age of the case was under 50 years old were as follows ; (1) strong link between tobacco and Buerger's disease was statistically reconfirmed. (2) cases consumed a less amount of milk than controls. (3) cases were engaged in physical works more frequently and under noisier and dustier environments than controls. (4) the past history of allergic rhinitis was found more on the side of cases. J Epidemiol, 1991; 1 : 19-25.
Annual numbers of patiens with the so-called intractable diseases were estimated in the nationwide epidemiological surveys under the assumption that the mean number of patients among “responded” hospitals is equal to that among “non-responded” hospitals. This paper evaluated the validity of this assumption, using the data of idiopathic thrombopenic purpura (ITP) obtained from the nationwide epidemiological survey and the number of ITP patients who are financially subsidized for treatment (FST-patients). The mean numbers of ITP FST-patients among “responded” hospitals in the nationwide survey were compared with the mean numbers among “non-responded” hospitals. The ratio of the mean number among “responded” hospitals to that among all hospitals was found to be between 1.0 and 1.1 ; suggesting that this assumption was sufficiently valid. J Epidemiol, 1991 ; 1 : 27-30.
Anti-HCV was examined in 454 patients on chronic hemodialysis(HD) in Fukuoka in 1990. The anti-HCV positive rate was significantly greater in those with than in those without blood transfusion (40.5% vs 11.7% for males, p<0.01, and 29.4% vs 5.6% for females, p<0.01). The anti-HCV positive rate increased with the duration of HD treatment among all patients except for the non-transfusion female patients. Blood transfusion thus appeared to be a major route of HCV infection in HD patients as had been reported previously. The anti-HCV positive rate was 2.6 times higher in those who had less than 5 years HD treatment but had never received a blood transfusion than found in the blood donors of Kitakyushu Red Cross Blood Center, adjusted by age. These results suggest that HD treatment might increase the exposure to HCV infection apart from blood transfusion. J Epidemiol, 1991 ; 1 : 31-36.