Editor,-

I welcome the publication of recent papers by Cherry and her collaborators.[1] [2] Although they form part of a large number of epidemiological studies, referenced by the authors, based solely on questionnaire data they do add significantly to the understanding of the ill-health of Gulf War Veterans (GWVs). The limitations of such studies are recognised by the authors, for example, the lack of any baseline information prior to the Gulf war, the lack of any exposure data for the period spent in the Gulf, and the absence of many records.

Once again there has been found an excess of the numbers and severity of symptoms amongst GWVs compared with a carefully chosen control group. It has been shown that these important and disturbing findings cannot be attributed to either excessive smoking or drinking amongst the veterans. The analysis of the data also clearly shows that the GWVs are reliable and accurate in their recall of information even in the extensive absence of official records. The abject failure in record keeping/preservation by the Ministry of Defence is again identified. However, 10 years after the Gulf War it is cause for considerable concern that only very limited clinical studies of the health of GWVs have been reported in the UK.

The first major finding identifies an association of severity of symptoms with pesticide handling in a manner that suggests a causal connection with peripheral neuropathies. This is new and accords with individual eyewitness accounts from the field[3] and some longstanding clinical studies. The second major finding confirms the association of symptoms and severity with the numbers of vaccines administered. It does not support the contentious and highly criticised,[4] and subsequently modified,[5] claim that only vaccines given in theatre were associated with excessive symptoms and severity.

The case made by the authors would have been considerably strengthened if they had recognised important clinical studies and investigations already carried out on some GWVs both in this country and the USA. Jamal et al have reported a small clinical study on UK veterans that identified peripheral neuropathy similar to that found in organophosphate-poisoned farmers.[6] [7] Mackness and coworkers have found, across all genotypes, a reduction of approximately 50% in the blood levels of PON 1, an enzyme with a key role in the metabolism organophosphate pesticides.[8] PON 1 plays an important protective role in the cardiovascular system[9] and in the aetiology of diabetes related damage.[10] In the United States Haley, whose epidemiology has been much criticised,[11][12][13] identified three major syndromes[14] [15] two of which, confusion-ataxia and arthro-myo-neuropathy, were associated with adverse reactions to NAPS tablets (pyridostigmine bromide). Arthro-myo-neuropathy syndrome was also strongly associated with the (excessive) use of the insect repellent DEET. Impaired cognition was associated with the wearing of flea collars. All these exposures feature prominently in the analysis carried out by Cherry and her co-workers.[1] [2] Crucially, after his epidemiological survey, Haley investigated the sick veterans clinically. He identified extensive and 'generalised injury to the central, peripheral, and autonomic nervous systems.'[16] More recent papers have shown both functional and structural deficits in the central nervous system including the left basal ganglia, and brain stem.[17] [18] This accords with the 'poor functioning of the central nervous system' associated by Cherry et al with their neurological factor which was not dissected further to explore only central nervous system effects. Haley has also shown significant variations in PON1 enzyme levels, which varied with the genotype.[19] Abou-Donia has shown, in animal studies, that there is synergism between insecticides of different classes, organophosphates and pyrethrins, which is exacerbated with DEET.[20] He has found specific antibodies to neuronal markers in one boy exposed to chlorpyrifos,[21] the major organophosphate used by the Americans in the Gulf. Despite the initial and vehement denial of the use of organophosphates by UK forces it emerged that these had been used extensively,[22] and with very little control.[3] [23] Furthermore the trained operatives were not supplied with effective protective clothing to carry out spraying and dusting with these insecticides.[3] [23]

Although UK authorities have strenuously denied any exposure to nerve agents and other chemical warfare agents,[24] it is clear that the Americans now recognise that a substantial number of their troops were exposed to low levels of nerve agents which produced only transient and in some cases no immediate symptoms.[17] [23] [26] Eye witness accounts support this view.[3] [26][27]

The 'cholinergic triple whammy' of NAPS, organophosphate insecticides, and nerve agents would be expected to exert severe and extensive effects on the central, peripheral, and autonomic nervous system. The use of NAPS has been heavily criticised,[28] and is consistent with the high incidence of side effects reported: approximately 50% in the army.[2]

Recently a tilt table study of the widespread loss of cardiovascular autonomic control among veterans has been announced in the United States.[29] Baumzweiger includes assessment of orthostatic hypotension in his examination and treatment of sick veterans in the United States.[30] All this evidence provides very convincing support for a causal relationship between exposure to NAPS, pesticides, and DEET in the health of the GWVs. The study provides very strong evidence for the reliability and accuracy of the responses by GWVs even in the absence of records-over all only 27.5% of GWVs have any vaccination records.

Although the Ministry of Defence has insisted that no more than 10 different vaccines were given to the veterans[24] [28] it is noteworthy that 11% reported receiving 10 or more vaccines. The association of ill health with numbers of vaccines administered is consistent with other studies.[31] What is lacking, along with most of the records, is the time frame for these inoculations. Adverse effects are well known when too many vaccines are administered too close together. The theoretical proposal of Rook and Zumla[32] concerning a possibly severe disturbance of the Th1/Th2 ratios is referred to, but not the work of Nicolson[33][34] and Vodjani[35] who have found mycoplasma species, particularly M fermentans incognitus, in about half of American veterans examined. These are also present in other chronic illnesses, myalgic encephalomyelitis, ME, fibromyalgia, and rheumatoid arthritis where a compromised immune system is thought to play an important role in the pathology. Repeat cycles of powerful antibiotics, with appropriate support for the gut, have proved an effective therapy in some of these cases.[36] A major study is presently under way in the States with doxycycline and ciprofloxacin.[37]

An important aspect of the widespread exposure to many and varied toxins in the Gulf is the question of synergy. Can the important data base assembled by these investigators be used to explore this question? Synergy is known for pesticide exposure.[20] The well documented effects of organophosphates on the immune system in man,[38] which were deliberately ignored by the COTS Committee,[39] provide a further example of possible synergistic or at least additive adverse effects. The immune system has suffered from more than the obvious exposure to vaccines.

Exposure to oil and smoke was consistently identified with severity (the best indicator) of symptoms but dropped from further consideration of the respiratory factor after allowing for other exposures. It is not clear what these factors are, but NAPS and organophosphates and vaccines are all known to exert profound effects on the respiratory system and would be expected to exert synergistic or additive adverse effects. Adverse effects from exposure to oil and smoke have been reported and would be expected,[40][41][42][43] although official publications deny any such possibilities.[44]

Although the authors report a study drawing attention to the importance of gastrointestinal symptoms[45] they do not emphasise the association with such symptoms in their own study. Table 6 in Part I shows that the gastrointestinal factor is significant in all veterans ranging from the essentially well (cluster 2) to the most severely affected (cluster 6). Our own preliminary studies have identified the importance of gastrointestinal dysfunction as a major factor, in a small sample of GWVS, which responds to dietary changes.[46]

The arbitrary division of exposures into three factors includes, 'factors reflecting individual susceptibilities'.[2] These encompass 'felt that life was in danger', sought medical attention in Gulf, and experienced side effects from NAPS. A much greater factor in personal susceptibilities is the biochemistry of the individual and his or her capacity for handling external chemical and biological toxic insults. The importance of the varied and extensive cytochrome P-450 enzymes confer remarkable variations in susceptibility to xenobiotics.[47] The association of genetic halotypes with some major chronic autoimmune diseases is well known.[48] This susceptibility could well lead to a range of vaccine induced illnesses. However the conflicting data on PON 1 levels[3][19] illustrates the urgent need for further studies of all these important issues.

The very low reporting of possible exposure to depleted uranium (DU) was understandable at the time the questionnaires were completed. However, recent events, including leaks of official military documents and memos,[24] [49][50] as well as the identification of DU in the urine of GWVs,[51] and people living in Yugoslavia,[52] indicate widespread exposure has occurred in areas where DU munitions have been used. An independent report commissioned by the American veterans surveyed 10 000 veterans and found the 75-80% had been in areas where they could have been exposed to DU.[53] [54]

The data and analysis presented in these papers is consistent with the thesis that the exposure of GWVs to an excessive load of many and varied chemical and biological toxins is responsible for the adverse health effects they are now suffering.[6][7] [14][15][16][17] [28] [54] M Hooper
School Sciences University of Sunderland UK

1. Cherry N, Creed F, Silman A, et al. Health and exposures of United Kingdom Gulf war veterans. Pt I: the pattern and extent of ill health. Occup Environ Med 2001;58:291-8.
2. Cherry N, Creed F, Silman A, et al. Health and exposures of United Kingdom Gulf war veterans. Pt II: The relation of health to exposure. Occup Environ Med 2001;58:299-306.
3. Worthington AJ. Information supplied to House of Commons Defence Committee, 1994-6. Testimony of Sgt. Worthington AJ, Environmental Health Technician on use of Pesticides. Commendation by Lt. Colonel BK Reece-Russell.
4 Hotopf A, David A, Hull L, et al. Role of vaccinations as risk factors for ill health in veterans of the Gulf war: cross sectional study. BMJ 2000;320:1363-7.
5 Electronic Letters by several authors in response to Hotopf paper available at bmj.com eLetters for Hotopf et al. BMJ 2000;320:1363-7.
6 Jamal GA, Hansen S, Apartopoulos F, et al. The 'Gulf War syndrome'. Is there evidence of dysfunction in the nervous system? J Neurol Neurosurg Psychiatry 1996;60:449-50.
7. Jamal, GA. Gulf War Syndrome-a model for the complexity of biological and environmental interaction with human health. Adverse Drug React Toxicol Rev 1998;17:1-17.
8. Mackness B, Durrington PN, Mackness MI. Low paraoxonase in Persian Gulf War veterans self-reporting Gulf War Syndrome. Biochem Biophys Res Comm 2000;276:729-33.
9. Mackness B, Hunt R, Durrington PN, et al. Increased immunolocalization of paraoxonase, clusterin, and apolipoprotein A-I in the human artery wall with the progression of atherosclerosis. Arterosclerosis thrombosis and Vascular Biology 1997;17:1233-8.
10. Mackness B, Mackness MI, Arrol S, et al. Serum paraoxonase (PON1) 55 and 192 polymorphism and paraoxonase activity and concentration in non- insulin dependent diabetes mellitus. Atherosclerosis 1998;139:341-9.
11. Wadman M. US panel draws blank on Gulf War symptoms. Nature 2000;407:121.
12. Wadman M. Fracas over $5 million Gulf syndrome grant. Nature 2001;410:135.
13. Haley RW. Gulf syndrome research has passed peer review. Nature 2001;410:739.
14. Haley RW, Kurt TL. Self-reported exposure to neurotoxic chemical Combinations in the gulf War: A Cross-sectional Epidemiologic Study. JAMA 1997;277:231-7.
15. Haley RW, Thomas LK, Horn J. Is there a Gulf War Syndrome: searching for syndromes by factor analysis of symptoms. JAMA 1997;277:215-22.
16. Haley RW, Horn J, Roland PS, et al. Evaluation of neurologic function in Gulf War Veterans. JAMA 1997;277:223-30.
17. Haley RW, Fleckenstein JL, Marshall WW, et al. Effect of basal ganglia injury on central dopamine activity in Gulf War Syndrome. Arch Neurol 2000;57:1280-3.
18. Roland PS, Haley RW, Yellin W, et al. Vestibular dysfunction in Gulf War Syndrome. Otolaryngol Head Neck Surg 2000;122:319-30.
19. Haley RW, Billecke S, La Du BN. Association of low PON1 Type Q (Type A) arylesterase activity with neurologic symptom complexes in Gulf War Veterans. Toxicol Appl Pharmacol 1999;157:227-33.
20. Abou-Donia MB, Wilmarth KR, Jensen KF, et al. Neurotoxicity Resulting from coexposure to pyridostigmine bromide, DEET, and permethrin: implications of Gulf War chemical exposures. J Toxicol Environ Health 1996;48:35-56.
21. Abou-donia MB, Garretson LK. Detection of neurofilament autoantibodies in human serum following induced neurologic disorder; a case report. Environmental Epidemiology and Toxicology 2000;2:37-41.
22. Further memorandum concerning the provision of advice to MOD Ministers between 1994 and 1996 on the subject of organophosphate pesticide use during the Gulf War. London: Ministry of Defence, October 1997.
23. Studham C. Information supplied by OP Information Network, Elizabeth Sigmund, to House of Commons Defence Committee, 1994-6. Testimony of a paramedic on use of malathion.
24. http://www.mod.uk/policy/gulfwar/index.htm.
25. Sarin. In: Gulf War and Health Fulco EF, Liverman CT, Sox HC (eds). Institute of Medicine, National Academy Press, 2000;1:5-22.
26. 2nd Report by the Committee on Government Reform and Oversight, Chairman Burton D. Union Calendar No. 228. 105th Congress, 1st Session House Report 105-338, November 1997.
27. Thomas W. Bringing the War Home. Anchorage: Earthpulse Press, 1998.
28. Hooper M. The Most Toxic War in Western Military History. Evidence submitted to the House of Commons Select Defence Committee, December 1999. Published in 7th Report of Defence Select Committee. Gulf Veterans' Illnesses. Report and proceedings of the Committee with Minutes of Evidence and Appendices, April 19th 2000.
29. Gulf War Study, John Hopkins University details at http://www.med.jhu.edu/gws/
30. Baumzweiger, W. Brainstem-Limbic Immune Dysregulation in 111 Gulf War Veterans: A Clinical Evaluation of its Etiology, Diagnosis and Response to Headache. International Journal of Medicine 1998;1:129-43.
31. Unwin C, Blatchley N, Coker W, et al. Health of UK servicemen who served in the Persian Gulf War. Lancet 1999;353,:169-78.
32. Rook G, Zumla A. Gulf War Syndrome: is it due to a systemic shift in cytokine balance towards a Th2 Profile? Lancet 1997;349:1831-3.
33. Nicolson GL, Nicolson, NL, Nasralla M. Mycoplasmal Infections and Fibromyalgia/Chronic Fatigue Illness (Gulf War Illness) Associated with Deployment to Operation Desert Storm. International Journal of Medicine 1997;1:80-92.
34. Nicolson GL. Chronic Infections as a Common Aetiology for many Patients with Chronic Fatigue Syndrome, Fibromyalgia Syndrome and Gulf War Illnesses. International Journal Medicine 1997;1:42-6.
35. Vojdani A, Franco AL. Multiplex PCR for the Detection of Mycoplasma fermentans, M. Hominis and M. penetrans in Patients with Chronic Fatigue Syndrome, Fibromyalgia, Rheumatoid Athritis, and Gulf War Syndrome. 1999;5:187-97.
36. Nicolson GL, Nasralla MY, Haier J, et al. Mycoplasmal Infections in Chronic Illnesses: Fibromyalgia and Chronic Fatigue Syndromes, Gulf War Illness, HIV-AIDS and Rheumatoid Arthritis. Medical Sentinel 1999;4:172-6.
37. Operations Manual Veterans Administration Cooperative Study #475 Antibiotic Treatment of Gulf War Veterans' Illnesses.
38. Repetto R, Baglia S. Pesticides and the Immune system: The Public Health Risks London: Earthscan Publications, 1996.
39. COTS Report. Organophosphates. Committee on the Toxicity of Chemicals in food, Consumer Products and the Environment, Woods HF Chairman, Crown copyright, 1999.
40. Petrucelli BP, Goldenbaum M, Scott B et al. Health effects of the 1991 Kuwait oil fires: a survey on the US Army troops. J Occup Environ Med 1999;41:433-9.
41. Stead CF. Oil Fires Petroleum and Gulf War Illness. Testimony to House SubCommmittee on Human Resources and Intergovernmental Relations, Chairman Shays C. June 26 1997. Stead CF. see also, http://www.ngwrc.org/OilSmoke/kuwait oil fire information.htm.
42. Testimony to the Presidential Advisory Committee on Gulf War Veterans Illnesses, March 26 1996.
43. Van Steenis D Incineration, Co-incineration and Health Memorandum to the House of Lords, Hansard 27 July 1999.
44. Gulf War Veterans' Illnesses: VA, DOD Continue to Resist Strong Evidence Linking Toxic Causes to Chronic Health Effects, in reference 26. See also http://www.gulflink.osd.mil?owf_ii/ the official Pentagon web site.
45. Ishoy T, Suadicani P, Guldanger B, et al. Risk factors for gastrointestinal symptoms. the Danish Gulf war study. Dan Med Bull 1999;46:420-3.
46. Hooper M. Guts, Brains and Gulf War Veterans. Conference Proceedings of Autism: Perspectives on Progress. Durham 5-7 April 2000. Sunderland: Autism Research Unit, University of Sunderland, UK, 2000.
47. Bland JS, Costarella L, Levin B, et al. Clinical Nutrition: A Functional Approach. Washington USA: The Institute for Functional Medicine, Gig Harbor, 1999:255ff.
48. Kuby J Immunology. 3rd Ed, New York: Freeman, 1997. 49. Memorandum for Headquarters, US Army Chemical School, 16 August 1993. This is just one example of several leaked documents. some now appear at the the web site in reference 24 above.
50. Fahey D. Case Narrative: Depleted Uranium (DU) Exposures, 1998. Available at National Gulf War Resource Center, Inc. 1224 M St, NW Washington, DC 20005, USA. http://www.gulfweb.org/ngwrc.
51. Durakoviæ A, Dietz KA, Horan P. Quantitative analysis of uranium isotopes in Canadian, US, and British Gulf War Veterans. Eur J Nucl Med 2000;27:5-75.
52. Civilians Contaminated by Depleted Uranium BBC 2 Scotland, Thursday 12 April 2001 19.30. Transcript http://www.bbc.co.uk/scotland/alba/programan/eorpa/transcripteng.shtml.
53. http://www.gulfweb.org/ngwrc.
54. Durakoviae A. On Depleted Uranium: Gulf War and Balkan Syndrome. Croatian Medical Journal 2001;42:130-4.

Editor

with regard to the limit of detection and to the data in table 5 and figure 5, the level of benzene in blood has given in µg/l. I believe that the correct indication should be in ng/l. As matter of fact, with a personal exposure to benzene of 9.3-3.8 µg/m3, it is impossible to have a blood benzene level of 213-195 µg/l which should be corresponding to an environmental exposure to benzene of more than 20 ppm (65 mg/m3). Francesco Brugnone

Editor-

Meredith et al,[1] performed a case referent study to investigate asthma caused by isocyanates. They claimed that the results indicated that isocyanate asthma occurs at low 8h average exposure (around 1.5 ppb); for exposures above 1.125 ppb there was about a three fold increased risk, however this was of limited statistical significance (OR=3.2, 95% CI 0.96- 10.6; p=0.06). They also concluded that their study, in contrast with other studies, showed a higher risk of isocyanate asthma in smokers and persons with atopy.

The study design is original as cases were recruited from a register of occupational asthma cases. A case reference study based on a register of cases with both the disease and the exposure of interest is new. I think the design requires some discussion as it may introduce severe bias.

A typical case-referent study selects cases with a certain disease- for example, asthma from a hospital register or in a population survey.[2] The referents should be selected in to give an unbiased estimate of exposure frequency in the study base.[3] The study base of a register, including occupational asthma cases, is the population that in the case of having asthma would be reported to the register. Therefore, the authors of this study matched the referents to the cases by reporting doctor and factory/production area. Then they measured/estimated the exposure level for both cases and referents and found that the average 8h exposure was higher among cases. This design has certain weaknesses illustrated by the following hypothetical situations:

1. Assume that the exposure in the production area is homogenous. Then both cases and referents would have the same exposure and the conclusion would be that the risk was independent of exposure level.

2. Assume that the reporting doctor only knows a proportion of incident cases, a reasonable assumption. If seeing the doctor is dependent on exposure level, a bias is obvious.

3. Assume that there was no increased risk at all in the workplaces at the current exposure but that there was exposure to irritants, which varied within the production area. Then cases with asthma would probably be more likely to report problems with their asthma to the occupational health physician. There would also be an association with all substances whose concentration was correlated to the irritant.

4. Assume that there was no causal association between the exposure and the occurrence of asthma at the current levels. As asthma is common among persons with atopy, the study would certainly indicate that atopy was a risk factor in combination with the exposure.

Some of these biases could be avoided if there was some specific test that with certainty established the causal association between asthma and the exposure among the cases. Asthma caused by isocyanates can with some certainty be established by provocation, but the study by Meredith included no routine provocation test.

If it is presumed that all the reported cases really are caused by isocyanates, a rather improbable assumption according to the case definition, the conclusion by the authors that isocyanate asthma occurs also at very low exposures without any threshold could be made without doing any case-referent analysis. They could just simply measure the exposure of the cases and conclude that the lowest measured exposure obviously caused isocyanate asthma. It is obviously impossible to determine any other threshold.

Is there a proper design of a case-referent study based on cases identified through a register where the association between exposure and outcome is already established? If the disease is caused by short term high exposure a case-crossover design seems possible.[3] However, that design requires a very accurate determination of when the disease started, which rarely is possible for asthma. Another possibility is to estimate the study base from which the cases are recruited-for example, in the study by Meredith et al[1] the number of person years in the different production areas where the cases were detected should have been estimated. This requires that all or most incident cases from that area is known or there should at least not be any differential reporting of cases between the areas.

Thus, the design of this study is interesting but includes many possibly bias of which a just a few were discussed in the paper. The conclusions that the risk of isocyanate asthma is increased at levels around 125 ppb, and is more common among persons with atopy and smokers are questionable.

Bengt Jarvholm, Department of Public Health and Clinical Medicine Umea University SE-901 85 Umea Sweden

1. Meredith SK, Bugler J, Clark RL. Isocyanate exposure and occupational asthma: a case referent study. Occup Environ Med 2000;57:830- 836.

2. Toren K, Jarvholm H, Hrisman J, et al. Adult onset asthma and occupational exposures. Scand J Work Environ Health 1999;25:430-5

3. Rothman KJ, Greenland S. Modern Epidemiology. (2nd ed) Philadelphia: Lippincott-Raven, 1998.

We read with interest the report by Desrosiers et al of the association between maternal occupational exposure to organic solvents and some birth defects [1]. Their case-control study examined occupational exposure to three classes of solvents (chlorinated, aromatic and Stoddard) and found one association -- between neural tube defects (mainly spinal bifida) and maternal occupational exposure to chlorinated solvents, but no association with the other solvent classes or with oral clefts. In their discussion, the authors noted that previous findings of maternal occupational exposure to solvents and oral clefts were from European, mainly French, populations and hypothesized that the inconsistency between their results and these previous studies might be due to different exposure profiles (e.g., intensity, solvent formulation). Although this explanation is plausible, another must be discussed: differences in the definition of exposure. Our research team conducted four of the five studies with positive results cited by Desrosiers et al[2][3][4][5]. All four were population based and included, in addition to the solvent classes considered by Desrosiers et al, oxygenated solvents, for example alcohols or glycol ethers. Exposure limited to only oxygenated solvents appears to be very frequent among working women: more than half of the solvent exposure group in Chevrier et al [4] were exposed only to that solvent class. Because previous studies found the increased risk of oral clefts to be associated principally with that specific exposure, the failure to consider this association could explain the negative findings for oral clefts. Moreover, women who were exposed only to oxygenated solvents are included in the reference ('non-exposed') group here, which would result in underestimating associations with chlorinated and petroleum solvents. For both these reasons, we think that the failure to consider oxygenated solvents led to underestimating the risk estimates for oral clefts.

1. Desrosiers, T.A., et al., Maternal occupational exposure to organic solvents during early pregnancy and risks of neural tube defects and orofacial clefts. Occup Environ Med 2012;69:7 493-499 Published Online First: 23 March 2012 doi:10.1136/oemed-2011-100245. 2. Cordier, S., et al., Maternal occupational exposure and congenital malformations. Scand J Work Environ Health, 1992. 18(1): p. 11-7. 3. Lorente, C., et al., Maternal occupational risk factors for oral clefts. Occupational Exposure and Congenital Malformation Working Group. Scand J Work Environ Health, 2000. 26(2): p. 137-45. 4. Chevrier, C., et al., Occupational exposure to organic solvent mixtures during pregnancy and the risk of non-syndromic oral clefts. Occup Environ Med, 2006. 63(9): p. 617-23. 5. Garlantezec, R., et al., Maternal occupational exposure to solvents and congenital malformations: a prospective study in the general population. Occup Environ Med, 2009. 66(7): p. 456-63.

Conflict of Interest:

None declared