1 Medical Science University of Baghyatollah (a.s.), School of Health, Department of Epidemiology and Biostatistics
2 Medical Science University of Tehran, School of Health, Department of Epidemiology and Biostatistics
Correspondence: A Karimi Zarchi, Medical Science University of Baghyatollah (a.s.), PO Box, 1655737316, Tehran, Iran. E-mail: alikarimi_in{at}yahoo.com
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Abstract |
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Methods In a retrospective cohort study of 1337 soldiers with a history of mustard gas exposure, factors such as age, smoking habit, number of exposure episodes, and the use of gas masks were determined, together with an assessment of their relationship to the occurrence of long-term pulmonary complications. All patients residing in the Tehran area were enrolled in the study. Data collection was based on the subjects' medical records and included clinical, spirometric, and in some cases histopathological findings.
Results The cumulative incidence rate of pulmonary complications was 31.6%; the lowest annual incidence rate was noted during the first year of follow-up (0.75/1000), and the highest rate recorded in the seventh year (76.9/1000). Estimated relative risks (RR) for various age groups are as follows: 1.13 (95% CI: 0.88, 1.46) for those aged 2125 years; 1.49 (95% CI: 1.10, 2.01) for ages 2630; 1.70 (95% CI: 1.20, 2.40) for ages 3135; and 2.09 (95% CI: 1.57, 2.77) for subjects aged 36. RR with regard to other factors were: more than one versus single exposure 0.69 (95% CI: 0.42, 1.12); smoking versus non-smoking 1.08 (95% CI: 0.80, 1.45), and unprotected exposure versus protective mask use 3.04 (95% CI: 2.20, 4.20).
Conclusion The estimated risk of pulmonary complications from war exposure to mustard gas increased with age and for soldiers who had not worn masks.
Accepted 6 November 2003
Sulphur mustard (mustard gas), the most widely used chemical agent in the IranIraq war,1 is a brownish yellow liquid with a garlic-like odour that boils at 228°C. It is unclear when this substance was first manufactured, but 1820, 1822, and 1845 have been cited by different authors.2,3 Mustard gas affects many organs including the skin, the gastrointestinal and respiratory tracts, and the central nervous system. The extent of tissue injury depends on the duration and intensity of exposure,46 and mortality is low (23%).7
To our knowledge, this is the first time that the annual incidence rate (AIR) and the cumulative incidence rate (CIR) for pulmonary lesions have being studied in terms of their relationship with factors such as age, exposure frequency, use of gas masks, and the victims' smoking habits.
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Materials and Methods |
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Data analysis
To obtain CIR, we divided the number of those with pulmonary lesions by the number of lesion-free individuals at the beginning of the study.9,10 For AIR, we divided the number of new cases in a year by the total person-years of follow-up in the same year.11 To compute relative risk (RR) for a particular factor, the incidence of lung lesions in the exposed group was divided by the incidence in the non-exposed group.12 We then used this approximative procedure,13 based on the error factor{exp [1.96 1/d0 + 1/d1]} to obtain 95% CI: multiplying and dividing the RR point estimate by this factor will yield the upper and lower confidence limits respectively. Data entry and analyses were made by Epi info (version 6.04) and Stata (version 4.0) software.14,15
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Results |
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Table 1 shows the frequency distribution of different age groups (mean age 25.5 years, SD 9.1 years). Some 1264 patients (94.5%) had been exposed only once, while 73 (5.5%) had experienced more than one exposure. The great majority (96.2%) were wearing gas masks at the time of poisoning, and 15.1% had a history of smoking cigarettes.
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Discussion |
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The histological features listed below are largely based on information from victims of chemical attacks in World War I; however, it should be borne in mind that because of the high prevalence of superimposed infections, it might be difficult to generalize these findings. Generally, light exposures only involve the upper respiratory tract but with more severe inhalation both the upper and lower tracts are affected.16
Clinical features, as summarized by Sohrabpour and Balali, include pulmonary/bronchial wheezing without consolidation, productive cough and, rarely, haemoptysis.17,18 In our study the low mortality rate meant that all patients were observed for the entire study period. The highest AIR of lung complications (76.9 per 1000) occurred in the seventh year, and the lowest (0.75 per 1000) in the first year. The risk appears to increase with age, with statistically significant elevations in all age categories except the 2125 years age group. Use of protective masks was found to decrease the occurrence of lung complications, i.e gas masks exerted a protective effect.
Smoking history and frequency of gas exposure were not associated with a significant rise in the risk of lung injury; this may be explained by ambient gas concentrations and duration of exposure and temperature.4 Thus, smoking history and frequency of gas exposure may not be the only main risk factors, and the role of age and gas mask protection may be more important.
KEY MESSAGES
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Acknowledgments |
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References |
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