- Email: [email protected]
Noncancer mortality (1987–1995) in high background radiation area of Yangjiang, China
International Congress Series 1225 (2002) 277 – 282
Noncancer mortality (1987–1995) in high background radiation area of Yangjiang, China Quanfu Suna,b,*, Jianming Zouc, Suminori Akibab, Jia Lia, Yusheng Liua, Zufan Taoa, Yongru Zhac, Tsutomu Sugaharad, Luxin Weia a
Laboratory of Industrial Hygiene, Ministry of Health, 2 Xinkang Street, Deshengmenwai, Beijing 100088, China b Department of Public Health, Faculty of Medicine, Kagoshima University, Sakuragaoka 8-35-1, Kagoshima 890-8520, Japan c Guangdong Institute of Prevention and Treatment of Occupational Diseases, 165 Xingangxi Road, Guangzhou 510310, China d Health Research Foundation, Pasteur Building 5F, 103-5 Tanaka-Monzen-Cho, Sakyo-Ku, Kyoto 606-8225, Japan
Keywords: Noncancer mortality; High background radiation area; Yangjiang
1. Introduction Extensive epidemiological studies have been carried out in a naturally occurring high background radiation area (HBRA) in Yangjiang of Guangdong Province, China since 1972 [1]. Inhabitants, mainly farmers, in the HBRA receive 6.4 m Sv every year from external and internal radiation exposures [2]. No excess cancer risk was found in the HBRA by a series of mortality analyses including the most recent one for the period 1979 –1995 [3,4]. Though noncancer death was not our primary endpoint of research, analyses were conducted for the periods 1979 –1986 and 1984– 1986. Using all the deaths observed during the period 1979 –1986, a statistically significant excess risk was found in the HBRA when compared to the control areas. Standardized mortality ratio (SMR) was calculated to be 1.07 (95% CI, 1.04 to 1.14) using mortality rates in a neighboring control area as reference [5]. In 1996, overall death rates were re-analyzed using updated mortality * Corresponding author. Research Centre for Radiation Safety, National Institute of Radiological Sciences, 4-9-1, Anagawa, Inaga, Chiba, 263-8555 Japan. Tel.: +81-43-206-3099; fax: +81-43-256-9882 E-mail address: [email protected] (Q. Sun). 0531-5131/02 D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 5 3 1 - 5 1 3 1 ( 0 1 ) 0 0 5 2 9 - 5
278
Q. Sun et al. / International Congress Series 1225 (2002) 277–282
data (1984 – 1986) [6]. Age- and sex-standardized overall death rates were 579.61 10 5 and 543.17 10 5 in the HBRA and its control area, respectively. Subsequent causespecific mortality analysis revealed excess risks of genitourinary diseases (nephritis) and neonatal diseases (tetanus, premature birth). The present paper reports further examinations of noncancer mortality rates among the residents in the HBRA and its control area using the updated mortality data for the period 1987 –1995.
2. Materials and methods The details of our follow-up study were described elsewhere [3]. Briefly, a fixed cohort was established in the HBRA and a nearby control area, and was followed-up by our task group for the period 1987 –1995. Task group visited all the villages once a year to check the demographic information collected and recorded by selected local villagers collaborating to our surveys. Once newly deceased was identified, our research group interviewed family members of the deceased and village doctors to collect information about the cause of death. In addition, the task group routinely visited all county hospitals in the study areas, and major hospitals in the province to retrieve relevant information from medical records. On the basis of information collected in this way, we determined causes of death and coded them according to the ninth revision of the International Classification of Diseases and Injuries (ICD-9) [7]. Risk estimation was based on the tabulated data, cross-classified by gender, age with 5year category, and follow-up period (1987 – 1989, 1990– 1992, 1993– 1995). The Poisson model [8] was used to estimate the relative risk comparing death rates in the HBRA with those in the control group.
3. Results During the period between 1987 and 1995, we followed 78,614 subjects and 27,903 subjects, accumulating 684,938 and 241,287 person – years in the HBRA and the control area, respectively. Those lost to follow-up numbered 1306 and 782, consisting 1.7% and 2.8% of the HBRA and the control populations, respectively. Totally, we observed 5161 deaths. Among them, 537 (10.4%) died from injuries and poisoning, 557 (10.8%) from malignancies, and 4067 (78.8%) from noncancer diseases. The relative risk comparing mortality for all causes of death in the HBRA with that in the control area was estimated to be 1.05 (95% CI, 0.99 to 1.11, P = 0.133). The slightly elevated mortality in the HBRA was due to diseases other than cancer. The relative risk of noncancer diseases was 1.09 (95% CI, 1.02 to 1.17, P = 0.014), indicating a statistically significant excess mortality in the HBRA. For cancer and injuries and poisoning, relative risk estimates were calculated to be 0.96 (95% CI, 0.80 to 1.15, P > 0.653), and 0.85 (95% CI, 0.71 to 1.02, P = 0.092), respectively. Table 1 shows the relative risk estimates for nine grand categories of causes of death. Those categories with number of cases less than 50 were not shown in Table 1. The six leading causes of death were
Q. Sun et al. / International Congress Series 1225 (2002) 277–282
279
Table 1 Relative risk of noncancer deaths (1987 – 1995) in high background radiation area, Yangjiang, China Rank
Cause of death
Cases
RR and 95% CI
p-value
1.07 0.96 0.85 1.07 0.81 1.46 1.41 1.74 1.56
0.136 0.636 0.092 0.518 0.036 0.004 0.082 0.070 0.190
(HBRA/control) 1 2 3 4 5 6 7 8 9
Diseases of the circulatory system Neoplasms Injury and poisoning Diseases of the respiratory system Infectious and parasitic diseases Diseases of the digestive system Diseases of the genitourinary system Mental disorders Symptoms, signs and ill-defined conditions
1701/686 395/165 371/166 366/146 283/148 246/70 109/32 52/12 41/10
(0.98 – 1.17) (0.80 – 1.45) (0.71 – 1.02) (0.88 – 1.29) (0.66 – 0.98) (1.12 – 1.90) (0.95 – 2.09) (0.93 – 3.26) (0.78 – 3.13)
accounted for 92% of all the deaths. The mortality of the diseases of digestive system in the HBRA was higher than the control area. Its relative risk was estimated to be 1.46 (95% CI, 1.12 to 1.90, P = 0.004). The difference of noncancer diseases other than the diseases of the digestive system in the HBRA and its control area was not significant (RR = 1.07 (95% CI, 0.99 to 1.14, P = 0.0789). On the other hand, deaths due to infectious and parasitic diseases were less common in the HBRA (RR = 0.81, 95% CI, 0.66 to 0.98, P = 0.036). The two most common diseases in the digestive system were chronic liver diseases and cirrhosis (ICD-9 code: 571, N = 112) and gastric and duodenal ulcer (ICD-9 code: 531 – 533, N = 52). Their relative risk estimates were 1.98 (95% CI, 1.21 to 3.24, P = 0.004) and 1.08 (95% CI, 0.59 to 1.97, P = 0.797), respectively. The mortality of diseases of the digestive system excluding chronic liver diseases and cirrhosis in the HBRA was not significantly different from that in the control area (RR = 1.26, 95% CI: 0.92– 1.73, P = 0.148). Among the infectious and parasitic diseases, pulmonary tuberculosis (ICD-9 code: 011) was the most common cause of death (N = 240), accounting for 55.7% of all deaths in this category. Its relative risk was 0.58 (95% CI, 0.45 to 0.75, P = 0.000). Relative risk of the infectious and parasitic diseases excluding pulmonary tuberculosis was 1.29 (95% CI, 0.93 to 1.80, P = 0.121). We also noted that suicide rate in the HBRA was lower than the control area. The relative risk was estimated to be 0.64 (95% CI, 0.45 to 0.90, P = 0.013).
4. Discussion Using the mortality follow-up data for the period of 1987– 1995, we found that the noncancer mortality among the population in the Yangjiang HBRA, China was increased by 9% compare to that in its control group. Specifically, we found an increased risk of the diseases of the digestive system including chronic liver diseases and cirrhosis. On the other hand, deaths due to infectious and parasitic diseases including pulmonary tuberculosis were less common in the HBRA. However, we have to admit that it is difficult to obtain
280
Q. Sun et al. / International Congress Series 1225 (2002) 277–282
reliable risk estimates of cause-specific diseases for most of the noncancer deaths using the current mortality data. One of our concerns in the analysis is ascertainment of the cause of death. Among 4067 deaths from noncancer diseases, only 23% were diagnosed in county hospitals or more advanced hospitals. Twelve percent of the noncancer diseases were diagnosed in township hospitals. Village doctors made 65% of the diagnoses (most of the cases, 1401/2643, were diseases of the circulatory system). These figures are much lower than those in our cancer mortality data reported elsewhere [3]. Briefly, 27% and 62% of all cancer cases (N = 557) were diagnosed with pathological findings and X-ray/ultrasonic examinations, respectively. Ninety percent of all cancer cases were diagnosed in county hospitals or more advanced hospitals. Of particular concern is the distinction between liver cancer and cirrhosis. Eighty-three percent of chronic liver diseases and cirrhosis were diagnosed in county hospitals or more advanced hospitals. We confirmed those medical diagnoses using medical records obtained from those hospitals. In the local hospitals, ultrasonic examination and alpha fetoprotein (AFP) test were the two most common approaches to differentiate cirrhosis of liver from liver cancer. The current databases did not provide detailed information about the use of AFP in distinguishing cirrhosis from liver cancer. In this mortality study, most cases (144/159) of liver cancer were diagnosed by ultrasonic examination only. When all the liver diseases, i.e. liver cancer, chronic liver diseases and cirrhosis (ICD-9 code: 151 and 557), were combined, the relative risk was 1.06 (95% CI, 0.81– 1.39, P = 0.648). In other words, the mortality of combined liver diseases in the HBRA was only 6% higher than the control area. It is difficult to entirely rule out the possibility that misclassification was at work in the observed increase of chronic liver diseases and liver cirrhosis in the HBRA. Since most of the residents in the HBRA and its control area were farmers, we assumed that the socioeconomic status and lifestyles in the two areas do not differ markedly. To date, surveys have revealed no distinct differences in lifestyles between the HBRA and the control area [9]. In one of such surveys conducted in our study area, we selected 90 and 30 households from the HBRA and the control area, respectively, and obtained information from 385 subjects (302 in the HBRA and 83 in the control area) during the period between October and December in 1993. We examined the daily intake of rice, wheat flour, sweet potatoes, and various vegetables, and found no statistically significant differences between the two areas. Lifestyle, including cigarette smoking and alcohol drinking, did not show significant difference between the two areas, either. Frequency of diagnostic X-ray examinations can be regarded as an index of medical care in countryside in China. Surveys of diagnostic X-ray examinations revealed that the reference population received a little more frequent diagnostic X-ray examinations than the population in the HBRA did [10]. For example, the frequencies of diagnostic X-ray examination in the HBRA for the year of 1977 –1978, 1982 and 1984 were 41.5, 41.0, and 53.3 per 1000 subjects, respectively. The corresponding figures were 34.8, 46.8, and 58.3 in the control area. The differences, however, were reported to be not statistically significant. We found a significant difference between the HBRA and the control area when infant mortality was used as a parameter of socioeconomic development. No infant mortality data were available for the period 1987 –1995. We analyzed infant death rates for the
Q. Sun et al. / International Congress Series 1225 (2002) 277–282
281
period of 1979 –1986 instead. Infant mortality rates in the HBRA in the control area were 30 and 19 per 1000, respectively. The relative risk comparing the infant mortality of the HBRA with that of the control area was 1.55 (95% CI, 1.24 to 1.94, P = 0.001), suggesting that the socioeconomic status including medical care was somewhat lower in the HBRA. Low socioeconomic status and chronic hepatitis, especially type B, are strongly related to liver cirrhosis in the developing countries. Two small pilot studies were carried out in Yangjiang HBRA [11,12]. The first survey, examining 400 subjects, revealed that the proportion of HBsAg positive middle-school students was 17% in the HBRA and 14% in the control area. The differences were not statistically significant, though. In the second survey, we examined HBcAb and HBsAg of 40 subjects, and found that the proportion of HBcAb positive in the HBRA (25%) was higher than the control area (20%). The proportion of HbsAge-positive was 25% in both the HBRA and its control area. We found that the death rate of pulmonary tuberculosis was lower in the HBRA. Relative risk was 0.58 (95% CI, 0.45 to 0.75, P < 0.001). Here again, accuracy of diagnosis is of concern. Sixty-eight percent of pulmonary tuberculosis was diagnosed in county hospital or more advanced hospitals. Unfortunately, we did not collect detailed information on the method of diagnosis, about pulmonary tuberculosis. Since the two neighboring areas were in the same prefecture, we could not expect a considerable difference of preventive measures taken by health authorities in the two areas. Unfortunately, no data of Bacille Calmette-Guerin (BCG) use was available for us to evaluate the effectiveness of prevention of tuberculosis. We estimated relative risks for several selected diseases for those subjects aged 50 years old or over. These subjects received cumulative doses of 50 years 6.4 m Sv/year = 320 m Sv from exposure to the high background radiation. We found that noncancer deaths excluding external causes were marginally higher in the HBRA than in the control area. The relative risk was 1.06 (95% CI, 0.99 to 1.14, P = 0.105). Relative risks of diseases of the digestive system, chronic liver diseases and cirrhosis, infectious and parasitic diseases, and pulmonary tuberculosis were estimated to be 1.31 (95% CI, 0.99 to 1.73, P = 0.057), 1.95 (95% CI, 1.12 to 3.41, P = 0.012), 0.76 (95% CI, 0.61 to 0.94, P = 0.013), and 0.52 (95% CI, 0.39 to 0.68, P = 0.000), respectively. The above results were similar to those obtained from using the subjects of all ages. In conclusion, analyzing cohort mortality data during the period 1987 –1995, we found that noncancer mortality in Yangjiang HBRA was higher than its control group by a factor of 1.09. Diseases of the digestive system, especially chronic liver diseases and cirrhosis were more common in the HBRA, and pulmonary tuberculosis was less common in the HBRA. Their relative risks were estimated to be 1.98 (95% CI, 1.21 to 3.24, P = 0.004) for chronic liver diseases and 0.58 (95% CI, 0.45 to 0.75, P < 0.001) for pulmonary tuberculosis. Many reasons may be responsible for these differences observed in this analysis, including lifestyle, socioeconomic status, and so on. We admitted that we had no reliable data on these factors though some surveys have been conducted in the investigated areas [9– 12]. At this moment, it is difficult to attribute those excess deaths in the HBRA to chronic radiation exposure since our data have their limitations. We think the most important factors related to the observed difference are the socioeconomic status including medical care and lifestyle-related factors. Future works including clinical follow-up of
282
Q. Sun et al. / International Congress Series 1225 (2002) 277–282
noncancer diseases, radiobiological studies, and confounding factor surveys, will be helpful to further understanding.
References [1] L.X. Wei (HBRRG), Health surveys in High-Background Radiation Areas in China, Science 209 (1980) 877 – 880. [2] L.X. Wei, Y.R. Zha, Z.F. Tao, W.H. He, D.Q. Chen, Y.L. Yuan, General report, in: L. Wei (Ed.), High Background Radiation Research in Yangjiang, China, Atomic Energy Press, Beijing, 1996, pp. 21 – 23. [3] Z.F. Tao, Y.R. Zha, S. Akiba, Q.F. Sun, J.M. Zou, J. Li, Y.S. Liu, H. Kato, T. Sugahara, L.X. Wei, Analysis of data from cancer mortality study in high background radiation area of Yangjiang, China, J. Radiat. Res. Suppl., (2000), 31 – 41. [4] Q.F. Sun, S. Akiba, Z.F. Tao, Y.L. Yuan, J.M. Zou, H. Morishima, H. Kato, Y.R. Zha, T. Sugahara, L.X. Wei, Excess relative risk of solid cancer mortality after prolonged exposure to naturally occurring highbackground radiation in Yangjiang, China, J. Radiat. Res. Suppl., (2000), 43 – 52. [5] Y.D. Pan, S.Y. Zhou, L.X. Wei, Mortality analysis of cancer and all causes of death from high background radiation research, Chin. J. Radiol. Med. Prot. 13 (1) (1993) 16 – 18. [6] R.L. Feng, Analysis of causes of death, in: L. Wei (Ed.), High Background Radiation Research in Yangjiang, China, Atomic Energy Press, Beijing, 1996, pp. 148 – 152. [7] World Health Organization, Manual of the International Statistical Classification of Disease, Injuries, and Cause of Death: Ninth Revision, World Health Organization, Geneva, 1975. [8] D.L. Preston, J.H. Lubin, D.A. Pierce, Epicure User’s Guide, HiroSoft International, Seattle, WA, 1993. [9] Y.R. Zha, J.M. Zou, Z.X. Lin, W.H. He, J.M. Lin, Y.H. Yang, H. Kato, Confounding factors in radiation epidemiology and their comparability between the high background radiation areas and control areas in Guangdong, China, in: L.X. Wei, T. Sugahara, Z.F. Tao (Eds.), High levels of Natural Radiation: Radiation Dose and Health Effects, Elsevier, Amsterdam, 1996, pp. 263 – 269. [10] Z.X. Lin, Comparability between investigated areas, in: L. Wei (Ed.), High Background Radiation Research in Yangjiang, China, Atomic Energy Press, Beijing, 1996, pp. 122 – 127. [11] M.Y. Li, H.W. Liu, Z.X. Lin, J.M. Lin, Y.R. Zha, Detection of hepatitis B surface antigen among the middleschool students in high background radiation area, Guangdong, Chin. J. Radiol. Med. Prot. 8 (2) (1988) 87. [12] J.M. Zou, J. Yao, N.G. Chen, Y.R. Zha, Studies on immune competence and immune response to virus among the inhabitants of high background radiation area, Yangjiang, China, Chin. J. Radiol. Med. Prot. 17 (6) (1997) 399 – 403.
Noncancer mortality (1987–1995) in high background radiation area of Yangjiang, China Quanfu Suna,b,*, Jianming Zouc, Suminori Akibab, Jia Lia, Yusheng Liua, Zufan Taoa, Yongru Zhac, Tsutomu Sugaharad, Luxin Weia a
Laboratory of Industrial Hygiene, Ministry of Health, 2 Xinkang Street, Deshengmenwai, Beijing 100088, China b Department of Public Health, Faculty of Medicine, Kagoshima University, Sakuragaoka 8-35-1, Kagoshima 890-8520, Japan c Guangdong Institute of Prevention and Treatment of Occupational Diseases, 165 Xingangxi Road, Guangzhou 510310, China d Health Research Foundation, Pasteur Building 5F, 103-5 Tanaka-Monzen-Cho, Sakyo-Ku, Kyoto 606-8225, Japan
Keywords: Noncancer mortality; High background radiation area; Yangjiang
1. Introduction Extensive epidemiological studies have been carried out in a naturally occurring high background radiation area (HBRA) in Yangjiang of Guangdong Province, China since 1972 [1]. Inhabitants, mainly farmers, in the HBRA receive 6.4 m Sv every year from external and internal radiation exposures [2]. No excess cancer risk was found in the HBRA by a series of mortality analyses including the most recent one for the period 1979 –1995 [3,4]. Though noncancer death was not our primary endpoint of research, analyses were conducted for the periods 1979 –1986 and 1984– 1986. Using all the deaths observed during the period 1979 –1986, a statistically significant excess risk was found in the HBRA when compared to the control areas. Standardized mortality ratio (SMR) was calculated to be 1.07 (95% CI, 1.04 to 1.14) using mortality rates in a neighboring control area as reference [5]. In 1996, overall death rates were re-analyzed using updated mortality * Corresponding author. Research Centre for Radiation Safety, National Institute of Radiological Sciences, 4-9-1, Anagawa, Inaga, Chiba, 263-8555 Japan. Tel.: +81-43-206-3099; fax: +81-43-256-9882 E-mail address: [email protected] (Q. Sun). 0531-5131/02 D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 5 3 1 - 5 1 3 1 ( 0 1 ) 0 0 5 2 9 - 5
278
Q. Sun et al. / International Congress Series 1225 (2002) 277–282
data (1984 – 1986) [6]. Age- and sex-standardized overall death rates were 579.61 10 5 and 543.17 10 5 in the HBRA and its control area, respectively. Subsequent causespecific mortality analysis revealed excess risks of genitourinary diseases (nephritis) and neonatal diseases (tetanus, premature birth). The present paper reports further examinations of noncancer mortality rates among the residents in the HBRA and its control area using the updated mortality data for the period 1987 –1995.
2. Materials and methods The details of our follow-up study were described elsewhere [3]. Briefly, a fixed cohort was established in the HBRA and a nearby control area, and was followed-up by our task group for the period 1987 –1995. Task group visited all the villages once a year to check the demographic information collected and recorded by selected local villagers collaborating to our surveys. Once newly deceased was identified, our research group interviewed family members of the deceased and village doctors to collect information about the cause of death. In addition, the task group routinely visited all county hospitals in the study areas, and major hospitals in the province to retrieve relevant information from medical records. On the basis of information collected in this way, we determined causes of death and coded them according to the ninth revision of the International Classification of Diseases and Injuries (ICD-9) [7]. Risk estimation was based on the tabulated data, cross-classified by gender, age with 5year category, and follow-up period (1987 – 1989, 1990– 1992, 1993– 1995). The Poisson model [8] was used to estimate the relative risk comparing death rates in the HBRA with those in the control group.
3. Results During the period between 1987 and 1995, we followed 78,614 subjects and 27,903 subjects, accumulating 684,938 and 241,287 person – years in the HBRA and the control area, respectively. Those lost to follow-up numbered 1306 and 782, consisting 1.7% and 2.8% of the HBRA and the control populations, respectively. Totally, we observed 5161 deaths. Among them, 537 (10.4%) died from injuries and poisoning, 557 (10.8%) from malignancies, and 4067 (78.8%) from noncancer diseases. The relative risk comparing mortality for all causes of death in the HBRA with that in the control area was estimated to be 1.05 (95% CI, 0.99 to 1.11, P = 0.133). The slightly elevated mortality in the HBRA was due to diseases other than cancer. The relative risk of noncancer diseases was 1.09 (95% CI, 1.02 to 1.17, P = 0.014), indicating a statistically significant excess mortality in the HBRA. For cancer and injuries and poisoning, relative risk estimates were calculated to be 0.96 (95% CI, 0.80 to 1.15, P > 0.653), and 0.85 (95% CI, 0.71 to 1.02, P = 0.092), respectively. Table 1 shows the relative risk estimates for nine grand categories of causes of death. Those categories with number of cases less than 50 were not shown in Table 1. The six leading causes of death were
Q. Sun et al. / International Congress Series 1225 (2002) 277–282
279
Table 1 Relative risk of noncancer deaths (1987 – 1995) in high background radiation area, Yangjiang, China Rank
Cause of death
Cases
RR and 95% CI
p-value
1.07 0.96 0.85 1.07 0.81 1.46 1.41 1.74 1.56
0.136 0.636 0.092 0.518 0.036 0.004 0.082 0.070 0.190
(HBRA/control) 1 2 3 4 5 6 7 8 9
Diseases of the circulatory system Neoplasms Injury and poisoning Diseases of the respiratory system Infectious and parasitic diseases Diseases of the digestive system Diseases of the genitourinary system Mental disorders Symptoms, signs and ill-defined conditions
1701/686 395/165 371/166 366/146 283/148 246/70 109/32 52/12 41/10
(0.98 – 1.17) (0.80 – 1.45) (0.71 – 1.02) (0.88 – 1.29) (0.66 – 0.98) (1.12 – 1.90) (0.95 – 2.09) (0.93 – 3.26) (0.78 – 3.13)
accounted for 92% of all the deaths. The mortality of the diseases of digestive system in the HBRA was higher than the control area. Its relative risk was estimated to be 1.46 (95% CI, 1.12 to 1.90, P = 0.004). The difference of noncancer diseases other than the diseases of the digestive system in the HBRA and its control area was not significant (RR = 1.07 (95% CI, 0.99 to 1.14, P = 0.0789). On the other hand, deaths due to infectious and parasitic diseases were less common in the HBRA (RR = 0.81, 95% CI, 0.66 to 0.98, P = 0.036). The two most common diseases in the digestive system were chronic liver diseases and cirrhosis (ICD-9 code: 571, N = 112) and gastric and duodenal ulcer (ICD-9 code: 531 – 533, N = 52). Their relative risk estimates were 1.98 (95% CI, 1.21 to 3.24, P = 0.004) and 1.08 (95% CI, 0.59 to 1.97, P = 0.797), respectively. The mortality of diseases of the digestive system excluding chronic liver diseases and cirrhosis in the HBRA was not significantly different from that in the control area (RR = 1.26, 95% CI: 0.92– 1.73, P = 0.148). Among the infectious and parasitic diseases, pulmonary tuberculosis (ICD-9 code: 011) was the most common cause of death (N = 240), accounting for 55.7% of all deaths in this category. Its relative risk was 0.58 (95% CI, 0.45 to 0.75, P = 0.000). Relative risk of the infectious and parasitic diseases excluding pulmonary tuberculosis was 1.29 (95% CI, 0.93 to 1.80, P = 0.121). We also noted that suicide rate in the HBRA was lower than the control area. The relative risk was estimated to be 0.64 (95% CI, 0.45 to 0.90, P = 0.013).
4. Discussion Using the mortality follow-up data for the period of 1987– 1995, we found that the noncancer mortality among the population in the Yangjiang HBRA, China was increased by 9% compare to that in its control group. Specifically, we found an increased risk of the diseases of the digestive system including chronic liver diseases and cirrhosis. On the other hand, deaths due to infectious and parasitic diseases including pulmonary tuberculosis were less common in the HBRA. However, we have to admit that it is difficult to obtain
280
Q. Sun et al. / International Congress Series 1225 (2002) 277–282
reliable risk estimates of cause-specific diseases for most of the noncancer deaths using the current mortality data. One of our concerns in the analysis is ascertainment of the cause of death. Among 4067 deaths from noncancer diseases, only 23% were diagnosed in county hospitals or more advanced hospitals. Twelve percent of the noncancer diseases were diagnosed in township hospitals. Village doctors made 65% of the diagnoses (most of the cases, 1401/2643, were diseases of the circulatory system). These figures are much lower than those in our cancer mortality data reported elsewhere [3]. Briefly, 27% and 62% of all cancer cases (N = 557) were diagnosed with pathological findings and X-ray/ultrasonic examinations, respectively. Ninety percent of all cancer cases were diagnosed in county hospitals or more advanced hospitals. Of particular concern is the distinction between liver cancer and cirrhosis. Eighty-three percent of chronic liver diseases and cirrhosis were diagnosed in county hospitals or more advanced hospitals. We confirmed those medical diagnoses using medical records obtained from those hospitals. In the local hospitals, ultrasonic examination and alpha fetoprotein (AFP) test were the two most common approaches to differentiate cirrhosis of liver from liver cancer. The current databases did not provide detailed information about the use of AFP in distinguishing cirrhosis from liver cancer. In this mortality study, most cases (144/159) of liver cancer were diagnosed by ultrasonic examination only. When all the liver diseases, i.e. liver cancer, chronic liver diseases and cirrhosis (ICD-9 code: 151 and 557), were combined, the relative risk was 1.06 (95% CI, 0.81– 1.39, P = 0.648). In other words, the mortality of combined liver diseases in the HBRA was only 6% higher than the control area. It is difficult to entirely rule out the possibility that misclassification was at work in the observed increase of chronic liver diseases and liver cirrhosis in the HBRA. Since most of the residents in the HBRA and its control area were farmers, we assumed that the socioeconomic status and lifestyles in the two areas do not differ markedly. To date, surveys have revealed no distinct differences in lifestyles between the HBRA and the control area [9]. In one of such surveys conducted in our study area, we selected 90 and 30 households from the HBRA and the control area, respectively, and obtained information from 385 subjects (302 in the HBRA and 83 in the control area) during the period between October and December in 1993. We examined the daily intake of rice, wheat flour, sweet potatoes, and various vegetables, and found no statistically significant differences between the two areas. Lifestyle, including cigarette smoking and alcohol drinking, did not show significant difference between the two areas, either. Frequency of diagnostic X-ray examinations can be regarded as an index of medical care in countryside in China. Surveys of diagnostic X-ray examinations revealed that the reference population received a little more frequent diagnostic X-ray examinations than the population in the HBRA did [10]. For example, the frequencies of diagnostic X-ray examination in the HBRA for the year of 1977 –1978, 1982 and 1984 were 41.5, 41.0, and 53.3 per 1000 subjects, respectively. The corresponding figures were 34.8, 46.8, and 58.3 in the control area. The differences, however, were reported to be not statistically significant. We found a significant difference between the HBRA and the control area when infant mortality was used as a parameter of socioeconomic development. No infant mortality data were available for the period 1987 –1995. We analyzed infant death rates for the
Q. Sun et al. / International Congress Series 1225 (2002) 277–282
281
period of 1979 –1986 instead. Infant mortality rates in the HBRA in the control area were 30 and 19 per 1000, respectively. The relative risk comparing the infant mortality of the HBRA with that of the control area was 1.55 (95% CI, 1.24 to 1.94, P = 0.001), suggesting that the socioeconomic status including medical care was somewhat lower in the HBRA. Low socioeconomic status and chronic hepatitis, especially type B, are strongly related to liver cirrhosis in the developing countries. Two small pilot studies were carried out in Yangjiang HBRA [11,12]. The first survey, examining 400 subjects, revealed that the proportion of HBsAg positive middle-school students was 17% in the HBRA and 14% in the control area. The differences were not statistically significant, though. In the second survey, we examined HBcAb and HBsAg of 40 subjects, and found that the proportion of HBcAb positive in the HBRA (25%) was higher than the control area (20%). The proportion of HbsAge-positive was 25% in both the HBRA and its control area. We found that the death rate of pulmonary tuberculosis was lower in the HBRA. Relative risk was 0.58 (95% CI, 0.45 to 0.75, P < 0.001). Here again, accuracy of diagnosis is of concern. Sixty-eight percent of pulmonary tuberculosis was diagnosed in county hospital or more advanced hospitals. Unfortunately, we did not collect detailed information on the method of diagnosis, about pulmonary tuberculosis. Since the two neighboring areas were in the same prefecture, we could not expect a considerable difference of preventive measures taken by health authorities in the two areas. Unfortunately, no data of Bacille Calmette-Guerin (BCG) use was available for us to evaluate the effectiveness of prevention of tuberculosis. We estimated relative risks for several selected diseases for those subjects aged 50 years old or over. These subjects received cumulative doses of 50 years 6.4 m Sv/year = 320 m Sv from exposure to the high background radiation. We found that noncancer deaths excluding external causes were marginally higher in the HBRA than in the control area. The relative risk was 1.06 (95% CI, 0.99 to 1.14, P = 0.105). Relative risks of diseases of the digestive system, chronic liver diseases and cirrhosis, infectious and parasitic diseases, and pulmonary tuberculosis were estimated to be 1.31 (95% CI, 0.99 to 1.73, P = 0.057), 1.95 (95% CI, 1.12 to 3.41, P = 0.012), 0.76 (95% CI, 0.61 to 0.94, P = 0.013), and 0.52 (95% CI, 0.39 to 0.68, P = 0.000), respectively. The above results were similar to those obtained from using the subjects of all ages. In conclusion, analyzing cohort mortality data during the period 1987 –1995, we found that noncancer mortality in Yangjiang HBRA was higher than its control group by a factor of 1.09. Diseases of the digestive system, especially chronic liver diseases and cirrhosis were more common in the HBRA, and pulmonary tuberculosis was less common in the HBRA. Their relative risks were estimated to be 1.98 (95% CI, 1.21 to 3.24, P = 0.004) for chronic liver diseases and 0.58 (95% CI, 0.45 to 0.75, P < 0.001) for pulmonary tuberculosis. Many reasons may be responsible for these differences observed in this analysis, including lifestyle, socioeconomic status, and so on. We admitted that we had no reliable data on these factors though some surveys have been conducted in the investigated areas [9– 12]. At this moment, it is difficult to attribute those excess deaths in the HBRA to chronic radiation exposure since our data have their limitations. We think the most important factors related to the observed difference are the socioeconomic status including medical care and lifestyle-related factors. Future works including clinical follow-up of
282
Q. Sun et al. / International Congress Series 1225 (2002) 277–282
noncancer diseases, radiobiological studies, and confounding factor surveys, will be helpful to further understanding.
References [1] L.X. Wei (HBRRG), Health surveys in High-Background Radiation Areas in China, Science 209 (1980) 877 – 880. [2] L.X. Wei, Y.R. Zha, Z.F. Tao, W.H. He, D.Q. Chen, Y.L. Yuan, General report, in: L. Wei (Ed.), High Background Radiation Research in Yangjiang, China, Atomic Energy Press, Beijing, 1996, pp. 21 – 23. [3] Z.F. Tao, Y.R. Zha, S. Akiba, Q.F. Sun, J.M. Zou, J. Li, Y.S. Liu, H. Kato, T. Sugahara, L.X. Wei, Analysis of data from cancer mortality study in high background radiation area of Yangjiang, China, J. Radiat. Res. Suppl., (2000), 31 – 41. [4] Q.F. Sun, S. Akiba, Z.F. Tao, Y.L. Yuan, J.M. Zou, H. Morishima, H. Kato, Y.R. Zha, T. Sugahara, L.X. Wei, Excess relative risk of solid cancer mortality after prolonged exposure to naturally occurring highbackground radiation in Yangjiang, China, J. Radiat. Res. Suppl., (2000), 43 – 52. [5] Y.D. Pan, S.Y. Zhou, L.X. Wei, Mortality analysis of cancer and all causes of death from high background radiation research, Chin. J. Radiol. Med. Prot. 13 (1) (1993) 16 – 18. [6] R.L. Feng, Analysis of causes of death, in: L. Wei (Ed.), High Background Radiation Research in Yangjiang, China, Atomic Energy Press, Beijing, 1996, pp. 148 – 152. [7] World Health Organization, Manual of the International Statistical Classification of Disease, Injuries, and Cause of Death: Ninth Revision, World Health Organization, Geneva, 1975. [8] D.L. Preston, J.H. Lubin, D.A. Pierce, Epicure User’s Guide, HiroSoft International, Seattle, WA, 1993. [9] Y.R. Zha, J.M. Zou, Z.X. Lin, W.H. He, J.M. Lin, Y.H. Yang, H. Kato, Confounding factors in radiation epidemiology and their comparability between the high background radiation areas and control areas in Guangdong, China, in: L.X. Wei, T. Sugahara, Z.F. Tao (Eds.), High levels of Natural Radiation: Radiation Dose and Health Effects, Elsevier, Amsterdam, 1996, pp. 263 – 269. [10] Z.X. Lin, Comparability between investigated areas, in: L. Wei (Ed.), High Background Radiation Research in Yangjiang, China, Atomic Energy Press, Beijing, 1996, pp. 122 – 127. [11] M.Y. Li, H.W. Liu, Z.X. Lin, J.M. Lin, Y.R. Zha, Detection of hepatitis B surface antigen among the middleschool students in high background radiation area, Guangdong, Chin. J. Radiol. Med. Prot. 8 (2) (1988) 87. [12] J.M. Zou, J. Yao, N.G. Chen, Y.R. Zha, Studies on immune competence and immune response to virus among the inhabitants of high background radiation area, Yangjiang, China, Chin. J. Radiol. Med. Prot. 17 (6) (1997) 399 – 403.