2013 Volume 55 Issue 5 Pages 415-421
Background: In industrializing countries, occupational safety and health have been affected by globalization. However, a lack of reliable data prevents evaluation of this situation. Therefore, we examined industrial distributions and risks of severe occupational injuries among workers in Thailand, which is one of the few industrializing countries that compiles nationwide data. Methods: Data on workers who made claims for occupational injuries from 2007 to 2009 were extracted from the Workmen's Compensation Fund records in Thailand. Among 501,334 claimants, we evaluated the industrial distributions of severe occupational injuries (i.e., permanent disability and death). We then examined the associations between industry and those injuries, using proportionate ratios (PRs) between each industrial category and the overall distribution of occupational injuries. Results: The number of workers in manufacturing making claims for severe occupational injuries was the largest among all industrial categories (319,114/501,334 injuries), although the total number of occupational injuries recently declined. Additionally, workers in manufacturing experienced severe occupational injuries more often compared with the overall distribution of occupational injuries. The PRs (95% confidence interval) for manufacturing were 1.17 (1.14-1.20) in men and 1.33 (1.27-1.38) in women. After adjusting for individual characteristics, the results did not substantially change. Conclusions: Manufacturing seems to have the largest burden of occupational injuries in industrializing countries like Thailand.
(J Occup Health 2013; 55: 415-421)
Occupational safety and health (OSH) have been profoundly affected by the processes of globalization1-3). Globalization stimulates intense global competition and mobility. Consequently, many manufacturing industries have shifted production to industrializing countries with lower labor costs and lax regulatory requirements related to OSH1, 2). In addition, in these countries, many workers are still employed in primary and extraction industries that are regarded as hazardous, including agriculture, mining, and construction1). With an increase in the proportion of manufacturing industries (mixed with primary and extraction industries), it is expected that not only workers in primary and extraction industries, but also those in manufacturing are experiencing an increase in occupational injuries. Although the International Labor Office has estimated occupational injuries in 175 countries, including industrializing countries, a lack of reliable data in industrializing countries prevents evaluation of this situation4, 5).
Previous studies in industrializing countries (e.g., Thailand6) and Vietnam7, 8)) have attempted to evaluate what occupation or industry was associated with occupational injuries. However, these studies did not use nationwide data and therefore could not provide individual risks related to the injuries in the countries.
Thailand is an industrializing country that has experienced rapid industrialization over the past 3 decades, which has been accompanied by the transition of industrial structures, and employment opportunities in Thailand are expanding for men and women9, 10). In 2009, it was estimated that 20.8 million men and 17.6 million women of the 63.5 million people in Thailand were employed11). However, unlike other industrializing countries, the Thai government has maintained nationwide recording and notification systems for occupational injuries because of a concern regarding an increase in the incidence of occupational injuries10, 12). Compilation of data is primarily performed by the Workmen's Compensation Fund (WCF). The WCF collects individual data on workers who made claims for occupational injuries, except for commuting injuries. This situation provides a unique opportunity to examine individual risks related to severe occupational injuries in industrializing countries.
Therefore, in the present study, we used claim records and attempted to evaluate demographic characteristics of severe occupational injuries among workers in Thailand. We then examined associations between industries and those injuries among the workers using proportionate ratios (PRs) between the distribution of each industrial category and the overall distribution. Both evaluations were conducted during the period of 2007 to 2009.
The WCF under the Social Security Office (SSO) in the Ministry of Labour is the principal provider of workers' compensation against occupational injuries or diseases. The coverage for workers' compensation, which we calculated from two sources (SSO and WCF), was approximately 21% of all the employed workers in 2009. The WCF covers workers in small-sized enterprises with one to nine workers13), although almost 30% of the covered workers were employed in large-sized enterprises with more than 500 workers. Most agricultural workers, self-employed workers, domestic workers and hourly workers and all civil servants are not covered by the WCF.
ParticipantsWe obtained occupational injury or disease claim records during the study period from the WCF (n=523,472). We excluded a total of 22,138 claimants, including those who made claims for occupational diseases (n=16,453), those whose injuries were categorized as unknown (n=937) and those whose industrial categories were unclassified (n=4,748). Finally, 501,334 claimants were included in both studies.
Industry categoriesIndustry is classified into 16 major industrial categories according to the Thailand Standard Industrial Classification, which is modified from the International Standard Industrial Classification (ISIC) of All Economic Activities. The 16 industrial categories are as follows: mining, manufacturing (manufacture of food and beverages, manufacture of textiles and accessories, forestry and wood products, paper products, printing, chemical products, petroleum, products from nonmetallic minerals, manufacture of basic metal, metal products, manufacture and assembly of vehicles, and other manufacturing industries), public utilities, construction, transport and communication, trade and other services. In the present study, we combined the categories of the 10 manufacturing-related industries into the new category of manufacturing. Subsequently, we had seven industrial categories as follows: mining, manufacturing, public utilities, construction, transport and communication, trade and other services. The trade industry included crops, ores and oil trade, building material trade and department stores.
Severity of injuriesIn the records, compensation claims consist of four categories according to the severity of injuries as defined by the WCF [i.e., death, permanent disability (partial, total), temporary disability with more than 3 working days lost, and temporary disability with less than 3 working days lost]. We classified these four categories into two subcategories: severe injuries, including permanent disability and death, and less-severe injuries, including temporary disability with more than 3 working days lost and temporary disability with 3 or less working days lost. The reasons for categorizing permanent disability and death as severe injuries were based on their irreversibility and serious impacts on workers themselves as well as families and society14).
Other covariatesWe extracted the following variables from the WCF records as other covariate data: age when the injury occurred, sex, size of enterprise, location of enterprise, claim year, and occupation. Size of enterprise was classified into eight categories according to the number of employees following the classification used by the SSO: 1 to 9, 10 to 19, 20 to 49, 50 to 99, 100 to 199, 200 to 499, 500 to 999 and 1,000 or greater. Location of enterprise was categorized into eight regions according to the WCF statistics as follows: Bangkok (the capital of Thailand), vicinity of Bangkok, Central, Western, Eastern, Northern, North-eastern and Southern regions. In the WCF, occupation is classified into nine major occupational categories according to the Thailand Standard Occupational Classification. In the present study, we used this WCF classification and categorized six occupational groups as follows: managers and professionals, clerks, craft and related trade workers, operators and assemblers, unskilled workers and others.
AnalysesIn descriptive analyses, we first compared demographic characteristics (age, sex, size of enterprise, location of enterprise, claim year, occupation and industry) among the four groups of severity of injuries.
The subsequent analyses were stratified by sex. We first calculated a proportion of permanent disability among all severities of injuries in each industrial category. We then calculated PRs for permanent disability, comparing the proportion of each industrial category with that of the total for all categories as a reference. We also calculated the 95% confidence intervals (CIs) for the PRs15). In a similar manner, we calculated PRs and their CIs for death.
As a supplemental analysis, we only used the individual data for claimants and evaluated which industry increased the risk of severe injuries relative to less-severe injuries. We stratified the claimants by sex and estimated the odds ratios with a logistic regression model, adjusting for age, size of enterprise, location of enterprise and claim year. We considered the trade category to be the reference category because occupational injury risks are relatively low in that industry16-18). Occupation was not used for adjustment because of a high correlation between industry and occupation.
All CIs were calculated at the 95% level. STATA statistical software (STATA SE version 12, StataCorp, College Station, TX, USA) was used for all the analyses.
Ethical issueThis study was submitted to and approved by the institutional review board at the Faculty of Medicine, Chulalongkorn University, on January 6, 2011 (No. 469/53 1/2011).
Demographic characteristics of claimants according to the severity of injuries are shown in Table 1. From 2007 to 2009, 398,655 male workers and 102,679 female workers claimed compensation to the WCF. Claims for permanent disability and death tended to be for older workers. Permanent disability and death occurred more frequently in smaller-sized enterprises than in larger-sized enterprises. Permanent disability occurred more frequently in the vicinity of Bangkok compared with other regions, whereas death occurred more frequently in the North-eastern region. During the 3 years, the number of claimants decreased across all severities of injuries.
| Temporary ≤3 d (n=355,901) | Temporary >3 d (n=125,795) | Permanent disability (n=17,759) | Death (n=1,879) | Total (n=501,334) | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Age (years), mean (SD) | 31.5 | (9.1) | 32.9 | (9.9) | 32.9 | (9.9) | 33.7 | (9.9) | 31.9 | (9.4) |
| Sex, n (row %) | ||||||||||
| Men | 283,222 | (71.0) | 100,291 | (25.2) | 13,405 | (3.4) | 1,737 | (0.4) | 398,655 | |
| Women | 72,679 | (70.8) | 25,504 | (24.8) | 4,354 | (4.2) | 142 | (0.1) | 102,679 | |
| Size of enterprise*, n. (row %) | ||||||||||
| <10 workers | 26,718 | (65.3) | 12,279 | (30.0) | 1,630 | (4.0) | 315 | (0.8) | 40,942 | |
| 10-19 workers | 27,376 | (67.3) | 11,662 | (28.7) | 1,394 | (3.4) | 253 | (0.6) | 40,685 | |
| 20-49 workers | 52,730 | (69.1) | 20,365 | (26.7) | 2,825 | (3.7) | 364 | (0.5) | 76,284 | |
| 50-99 workers | 45,797 | (70.6) | 16,413 | (25.3) | 2,410 | (3.7) | 229 | (0.4) | 64,849 | |
| 100-199 workers | 53,849 | (71.8) | 18,166 | (24.2) | 2,788 | (3.7) | 230 | (0.3) | 75,033 | |
| 200-499 workers | 67,450 | (72.8) | 21,751 | (23.5) | 3,266 | (3.5) | 236 | (0.3) | 92,703 | |
| 500-999 workers | 36,605 | (73.9) | 11,101 | (22.4) | 1,747 | (3.5) | 103 | (0.2) | 49,556 | |
| ≥1,000 workers | 45,376 | (74.0) | 14,058 | (22.9) | 1,699 | (2.8) | 149 | (0.2) | 61,282 | |
| Location of enterprise, n. (row %) | ||||||||||
| Bangkok | 106,259 | (73.3) | 35,082 | (24.2) | 3,103 | (2.1) | 546 | (0.4) | 144,990 | |
| Vicinity of Bangkok | 121,123 | (70.2) | 41,642 | (24.1) | 9,379 | (5.4) | 337 | (0.2) | 172,481 | |
| Central region | 32,032 | (71.1) | 11,396 | (25.3) | 1,433 | (3.2) | 170 | (0.4) | 45,031 | |
| Western region | 10,716 | (67.6) | 4,544 | (28.7) | 506 | (3.2) | 83 | (0.5) | 15,849 | |
| Eastern region | 41,538 | (77.8) | 10,269 | (19.2) | 1,429 | (2.7) | 148 | (0.3) | 53,384 | |
| Northern region | 16,279 | (68.3) | 6,789 | (28.5) | 570 | (2.4) | 193 | (0.8) | 23,831 | |
| North-eastern region | 14,451 | (67.8) | 5,842 | (27.4) | 798 | (3.7) | 218 | (1.0) | 21,309 | |
| Southern region | 13,503 | (55.2) | 10,231 | (41.8) | 541 | (2.2) | 184 | (0.8) | 24,459 | |
| Claim year, n. (row %) | ||||||||||
| 2007 | 134,348 | (71.5) | 46,049 | (24.5) | 6,870 | (3.7) | 696 | (0.4) | 187,963 | |
| 2008 | 121,145 | (71.0) | 42,271 | (24.8) | 6,516 | (3.8) | 611 | (0.4) | 170,543 | |
| 2009 | 100,408 | (70.3) | 37,475 | (26.2) | 4,373 | (3.1) | 572 | (0.4) | 142,828 | |
| Occupation, n. (row %) | ||||||||||
| Clerks | 8,524 | (65.8) | 4,028 | (31.1) | 275 | (2.1) | 138 | (1.1) | 12,965 | |
| Managers and professionals | 10,944 | (72.1) | 3,838 | (25.3) | 283 | (1.9) | 125 | (0.8) | 15,190 | |
| Craft and related trade workers | 111,157 | (73.9) | 34,180 | (22.7) | 4,708 | (3.1) | 419 | (0.3) | 150,464 | |
| Operators and assemblers | 142,136 | (69.0) | 52,802 | (25.7) | 10,326 | (5.0) | 631 | (0.3) | 205,895 | |
| Unskilled workers | 44,495 | (70.9) | 16,596 | (26.5) | 1,298 | (2.1) | 354 | (0.6) | 62,743 | |
| Others | 38,645 | (71.5) | 14,351 | (26.5) | 869 | (1.6) | 212 | (0.4) | 54,077 | |
| Industry, n. (row %) | ||||||||||
| Trade | 42,484 | (70.6) | 16,251 | (27.0) | 1,099 | (1.8) | 311 | (0.5) | 60,145 | |
| Mining | 1,317 | (55.1) | 959 | (40.1) | 83 | (3.5) | 32 | (1.3) | 2,391 | |
| Manufacturing | 225,103 | (70.5) | 78,925 | (24.7) | 14,512 | (4.6) | 574 | (0.2) | 319,114 | |
| Public utilities | 882 | (58.1) | 524 | (34.5) | 56 | (3.7) | 55 | (3.6) | 1,517 | |
| Construction | 39,058 | (76.1) | 11,037 | (21.5) | 945 | (1.8) | 303 | (0.6) | 51,343 | |
| Transport and communication | 10,206 | (62.2) | 5,447 | (33.2) | 433 | (2.6) | 335 | (2.0) | 16,421 | |
| Other services | 36,851 | (73.1) | 12,652 | (25.1) | 631 | (1.3) | 269 | (0.5) | 50,403 | |
n: number. Temporary ≤3 d: temporary disability with 3 or less working days lost. Temporary >3 d: temporary disability with more than 3 working days lost. Mining: survey and mining.
Occupational and industrial characteristics are also shown in Table 1. With regard to occupation, operators and assemblers suffered from permanent disability most frequently. With regard to industry, permanent disability occurred most frequently in workers in manufacturing, although death occurred most frequently in workers in public utilities. A large proportion of operators and assemblers (91% in men and 99% in women) were involved in the industrial category of manufacturing in the present data set.
The distribution of industries among the severity of injuries is shown in Table 2. In both sexes, PRs of severe occupational injuries, including permanent disability and death, were significantly elevated in the manufacturing category. The PRs (95% CIs) were 1.17 (1.14-1.20) in men and 1.33 (1.27-1.38) in women. In men, the PRs were also significantly elevated in public utilities, mining and transport and communication categories.
| All injuries | Severe injuries* | Pr | PR† | 95% CI | Permanent disability | Pr | PR† | 95% CI | Death | Pr | PR† | 95% CI | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| [n] | [n] | [%] | [-] | [n] | [%] | [-] | [n] | [%] | [-] | ||||
| Men | |||||||||||||
| Total | 398,655 | 15,142 | 3.80 | 1 (ref.) | 13,405 | 3.36 | 1 (ref.) | 1,737 | 0.44 | 1 (ref.) | |||
| Industry | |||||||||||||
| Trade | 50,186 | 1,223 | 2.44 | 0.64 | (0.61-0.68) | 936 | 1.87 | 0.56 | (0.52-0.59) | 287 | 0.57 | 1.30 | (1.14-1.47) |
| Mining | 2,163 | 105 | 4.85 | 1.28 | (1.06-1.54) | 77 | 3.56 | 1.06 | (0.85-1.32) | 28 | 1.29 | 2.93 | (2.02-4.25) |
| Manufacturing | 250,675 | 11,113 | 4.43 | 1.17 | (1.14-1.20) | 10,586 | 4.22 | 1.26 | (1.22-1.29) | 527 | 0.21 | 0.48 | (0.43-0.53) |
| Public utilities | 1,475 | 108 | 7.32 | 1.93 | (1.61-2.31) | 53 | 3.59 | 1.07 | (0.82-1.39) | 55 | 3.73 | 8.48 | (6.51-11.03) |
| Construction | 44,234 | 1,125 | 2.54 | 0.67 | (0.63-0.71) | 844 | 1.91 | 0.57 | (0.53-0.61) | 281 | 0.64 | 1.45 | (1.28-1.65) |
| Transport and communication | 14,883 | 711 | 4.78 | 1.26 | (1.17-1.35) | 392 | 2.63 | 0.78 | (0.71-0.86) | 319 | 2.14 | 4.86 | (4.32-5.47) |
| Other services | 35,039 | 757 | 2.16 | 0.57 | (0.53-0.61) | 517 | 1.48 | 0.44 | (0.40-0.48) | 240 | 0.68 | 1.55 | (1.35-1.77) |
| Women | |||||||||||||
| Total | 102,679 | 4,496 | 4.38 | 1 (ref.) | 4,354 | 4.24 | 1 (ref.) | 142 | 0.14 | 1 (ref.) | |||
| Industry | |||||||||||||
| Trade | 9,959 | 187 | 1.88 | 0.43 | (0.37-0.50) | 163 | 1.64 | 0.39 | (0.33-0.45) | 24 | 0.24 | 1.71 | (1.11-2.64) |
| Mining | 228 | 10 | 4.39 | 1.00 | (0.55-1.84) | 6 | 2.63 | 0.62 | (0.28-1.37) | 4 | 1.75 | 12.50 | (4.67-33.48) |
| Manufacturing | 68,439 | 3,973 | 5.81 | 1.33 | (1.27-1.38) | 3,926 | 5.74 | 1.35 | (1.30-1.41) | 47 | 0.07 | 0.50 | (0.36-0.70) |
| Public utilities | 42 | 3 | 7.14 | 1.63 | (0.55-4.86) | 3 | 7.14 | 1.68 | (0.57-5.01) | 0 | 0 | (-) | (-) |
| Construction | 7,109 | 123 | 1.73 | 0.40 | (0.33-0.47) | 101 | 1.42 | 0.33 | (0.28-0.41) | 22 | 0.31 | 2.21 | (1.41-3.47) |
| Transport and communication | 1,538 | 57 | 3.71 | 0.85 | (0.66-1.09) | 41 | 2.67 | 0.63 | (0.46-0.85) | 16 | 1.04 | 7.43 | (4.44-12.43) |
| Other services | 15,364 | 143 | 0.93 | 0.21 | (0.18-0.25) | 114 | 0.74 | 0.17 | (0.15-0.21) | 29 | 0.19 | 1.36 | (0.91-2.02) |
n: number. Pr: proportion. PR: proportionate ratio. CI: confidence interval. Mining: survey and mining. *Severe injuries (severe occupational injuries) included permanent disability and death. †The PR represented the ratio of permanent disability and death, which was calculated by comparing the proportion of each industrial category with that of the total for all categories as a reference.
In the supplementary analysis, odds ratios (ORs) for associations of industry with severe injuries relative to less-severe injuries were estimated (Table 3). In men, the adjusted OR (aOR) was the highest in public utilities category (aOR: 3.09; 95% CI: 2.52-3.79), followed by transport and communication and mining categories. In women, the aOR was the highest in public utilities category (aOR: 4.20; 95% CI: 1.27-13.85), followed by manufacturing and mining categories.
| Industry | Men | Women | ||||||
|---|---|---|---|---|---|---|---|---|
| cOR | 95% CI | aOR* | 95% CI | cOR | 95% CI | aOR* | 95% CI | |
| Trade† | 1 (ref.) | 1 (ref.) | 1 (ref.) | 1 (ref.) | ||||
| Mining | 2.04 | (1.67-2.51) | 1.90 | (1.54-2.33) | 2.40 | (1.25-4.59) | 2.55 | (1.32-4.90) |
| Manufacturing | 1.86 | (1.75-1.97) | 1.78 | (1.67-1.89) | 3.22 | (2.78-3.73) | 3.68 | (3.16-4.28) |
| Public utilities | 3.16 | (2.58-3.88) | 3.09 | (2.52-3.79) | 4.02 | (1.23-13.12) | 4.20 | (1.27-13.85) |
| Construction | 1.04 | (0.96-1.13) | 1.10 | (1.01-1.20) | 0.92 | (0.73-1.16) | 1.26 | (1.00-1.59) |
| Transport and communication | 2.01 | (1.83-2.21) | 1.96 | (1.79-2.16) | 2.01 | (1.49-2.72) | 2.10 | (1.55-2.84) |
| Other services | 0.88 | (0.81-0.97) | 0.97 | (0.88-1.06) | 0.49 | (0.39-0.61) | 0.61 | (0.49-0.76) |
cOR: crude odds ratio. aOR: adjusted odds ratio. CI: confidence interval. Ref.: reference. *Age, size of enterprise, location of enterprise and claim year were adjusted for. †Reference category.
We used individual data from claim records maintained by the WCF in Thailand and evaluated the industrial distributions of severe occupational injuries. As expected, the number of workers making claims for permanent disability and death in the manufacturing category was the largest among the industrial categories, although the total number of occupational injuries declined from 2007 to 2009. Moreover, these workers made claims for severe occupational injuries more often compared with the overall distribution of occupational injuries. Even after adjusting for individual characteristics, the results did not substantially change. This is the first nationwide report to examine the industrial distributions and risks of severe occupational injuries among workers in Thailand.
In the present study, workers in manufacturing experienced severe injuries (i.e., permanent disability and death) more frequently compared with the overall distribution of occupational injuries (Table 2). Similarly, elevated rates were observed for manufacturing in previous studies in Vietnam8) and other industrializing countries1, 17, 19).
Caution is warranted in interpreting the results from the supplementary analysis shown in Table 3. The aORs show the extent of discrepancy in the distribution of severe injuries relative to that of less-severe injuries. As mentioned above, Thailand has experienced a transition of industrial structures (i.e., a mix of primary, extraction, manufacturing, and service industries) similar to other industrializing countries. In Thailand, workers in manufacturing also suffered from a higher risk of severe injuries even if we accounted for the distribution of less-severe injuries (i.e., elevated PRs of permanent disability in manufacturing as shown in Table 2).
In addition to manufacturing, several industries, such as mining, public utilities and transport and communication, had elevated proportions of severe injuries compared with the overall distribution of occupational injuries, but only in men. Thepaksorn et al.6) found that electrical current was the biggest mechanism of fatal occupational injuries using a hospital-based surveillance system in Thailand, which may be consistent with the present findings in public utilities. Although some of our results are comparable with the results of studies in industrialized countries16-18, 20, 21), China22) and Taiwan23), it should be noted that the numbers of injuries in mining, public utilities and transport and communication were small (Table 1). Future studies using the exact number of workers in these industries as denominators could provide further insights.
An important limitation in the present study is that the coverage of employees by the WCF in Thailand is limited (i.e., only 21%). In particular, the WCF does not cover most agricultural workers, self-employed workers, domestic workers and hourly workers and does not cover any civil servants. In particular, agricultural workers account for 40% of the employed workers in Thailand11). Although workers in manufacturing are reported to suffer from occupational injuries more often than those in agriculture in Vietnam8), agriculture is well known as one of the most hazardous types of work in industrializing1) and industrialized countries16-18, 21). Moreover, WCF records do not fully capture migrant workers within Thailand and those from neighboring countries. These workers tend to temporarily or seasonally engage in unskilled work or work in specific industries, such as mining, construction, and fish processing or garment manufacturing24). Therefore, this limited coverage would affect the external validity of the present findings with respect to all workers in Thailand.
Underreporting of occupational injuries is likely4), as suggested by low statistics in the present study, such as 142,828 total injuries per 38.4 million workers in 2009 (only 3 per 1,000 covered workers). This underreporting might be different across industries. Furthermore, reporting of occupational injuries could be influenced by sex25, 26). Therefore, these factors would also affect external validity. However, underreporting would not change the present results substantially considering the similar findings in previous studies as mentioned above.
Residual confounding cannot be ruled out. In some cases, the location of the enterprise, which we used as a potential confounder, indicated the location of the headquarters rather than the location where the injuries occurred. However, this residual confounding is not large enough to change the present results.
Finally, we could not differentiate the first and subsequent claims of some individuals in the WCF records because no codes to identify claimants were included in the records. However, repeated injuries may be rare in Thailand. Thus, we can assume that all of the claims were independent.
In conclusion, in spite of the limitation of external validity due to the limited study population, we found that the number of workers in manufacturing making claims for severe occupational injuries was the largest among all industrial categories in Thailand (319,114/501,334 injuries). Furthermore, workers in manufacturing experienced severe injuries more often than those in other industries. Future studies to address factors related to elevated risks of severe injuries for manufacturing among the total insured workers are warranted.
Competing interests: None declared.
Funding: This study was supported by a grant for the purpose of overseas study from the Konosuke Matsushita Memorial Foundation (Grant No. 08-008).
Acknowledgment: The authors would like to thank the Secretary General of the Social Security Office, the Director and the concerned staff, including Anchana Phonghiruncharoen, of the Workmen's Compensation Fund. We thank Dr. Vitool Lohsoonthorn for his technical advice. We also thank all personnel in the Department of Preventive and Social Medicine, Faculty of Medicine, Chulalongkorn University. Finally, we express our thanks to Panadda Roongruangratanakul, Nophapat Padermwong and Jaturong Thammajinda for helping us conduct the study in Thailand and to Tomoko Kobayashi and Akiko Tokinobu for helping us collect materials.
