The Prevalence of Gout in Three English Towns

Transcription

1 International Journal of Epidemiology Oxford University Press 82 Vol. 11, No. 1 Printed in Great Britain The Prevalence of Gout in Three English Towns M J GARDNER*. C POWER". D J P BARKER* and R PADDAY* Gardner M J [MRC Environmental Epidemiology Unit, University of Southampton], Power C, Barker D J P and Padday R.The prevalence of in three English towns. International Journal ofepidemiology 82,11: The prevalence of has been measured in three English towns by means of a postal questionnaire. The three towns were selected to give a range of socio-economic conditions. In each town questionnaires were sent to a sample of approximately 5000 men aged 5 to 7 years. The questionnaire elicited a history of and a history of an attack of severe in the great toe. There was a progressive increase in prevalence of from, the town with the most favourable socio-economic status, through to, the town with the least favourable socio-economic status. Within each town there was no difference between the social class distribution of and age-matched. There are marked geographical variations in the prevalence of. For example, surveys in Northern Holland and Bulgaria revealed no patients with the disease; in Leigh, England the five-year period prevalence among men aged and over was per 0; in New Zealand the life-time period prevalence in a population of Caucasian men aged 20 and over was 20 per 0; and in Framingham, America, the life-time period prevalence of men aged to 71 was 28 per 0. 1 In Britain has been traditionally regarded as being less common in Scotland than England; 2 and this belief was supported by a recent survey based on general practitioner consultation rates. Gout is traditionally known as a disease of higher social classes ('the arthritis of the rich'). Given the variations in socio-economic conditions from one part of Britain to another it could be predicted that there would be variations in the prevalence of. This paper describes the results of a survey of in three English towns. The towns were selected to give a range of socio-economic conditions. METHODS The 8 largest county boroughs in England and Wales were classified into three groups having 'better', 'intermediate' and 'worse' social and economic conditions. This classification was effected using a range of intercorrelated social and economic indices, and has been described in detail elsewhere. The towns selected for the * MRC Environmental Epidemiology Unit, University of Southampton. South Academic Block, Southampton General Hospital, Southampton, SO9 XY. survey were, a 'better' town,, an 'intermediate' town and a 'worse' town. These towns comprise three of nine British towns in which morbidity from a range of disorders is being studied. To study in all nine towns would have been prohibitively expensive. A postal questionnaire was designed to elicit a history of. The questions asked the respondent if he or she had ever had, or had had an attack of extremely severe in the big toe the commonest manifestation of acute. This questionnaire was initially tested by interviews with patients attending a rheumatology clinic. Subsequently it was mailed to patients in three general practices in Southampton. In the last of the three mailings, with the wording of the questionnaire in its final form, 5 out of 9 people replied (a response rate of 90) and among the respondents with and the without there were no false positive or false negative responses to the question 'have you ever had?' Although the sample is not large this suggests that the question is a valid method of detecting. The criteria for the diagnosis of in the was a typical history of acute arthritis, usually in the big toe, leading to investigation and diagnosis by the general practitioner or consultant. The prevalence of is higher in men than in women. In order to obtain adequate numbers of without using excessively large samples the survey was therefore restricted to men aged 5-7 years. In each town a sample of men was obtained from the Family Practitioner Committee (FPC) listings of persons registered with general practitioners. One doctor was selected at random from each group practice and a random sample of single-handed practices was taken. 71

2 72 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY TABLE 1 Replies to postal questionnaire received after two mailings of men in sample of replies received 92(8) 82(81) 27(82) of completed questionnaires 807(71) 2(8) 109() Figures in brackets are percentages of total sample in each town. All men within the age range on the lists of the selected doctors were included in the final sample of approximately 5000 men in each town. This sample size was based on an estimated prevalence of, a figure derived from the Framingham study. 7 With a response rate of 75 a difference of 1 or more between any two towns would be statistically significant. Each man in the sample was sent a questionnaire together with a reply paid envelope. Those not replying within a month were sent a second questionnaire and an accompanying letter. RESULTS Table 1 shows the number of men in the samples and the numbers of replies received in each town. The return rates after two mailings ranged from 81 to 8. Of the returns 1059 (82) contained completed questionnaires. The reasons for not being completed included 'person not known,' 'gone away', 'no such address' and 'house demolished'. Four per cent of questionnaires sent to were returned with a statement that the house had been demolished. Only a few such returns were received from or. This is the principle reason why the percentage of completed questionnaires from () was lower than that from (71) and (8). In each town the stated age of a small number of men differed from that given in the FPC records and fell outside the range 5 to 7 years. They were excluded from the analysis which is therefore restricted to 10 questionnaires rather than the total completed questionnaires. TABLE 2 Age-specific period prevalence of * among men in the three towns Table 2 shows the answers to the question, 'Have you ever had?' analysed by age in each town. The figures are period prevalences the period being the lifetimes of the men. The overall prevalences increase from.9 in, to.5 in, to.8 in. These figures are not altered by standardisation to allow for differences in age distribution in the towns. The differences between the three towns do not reach the conventional level of statistical significance (X 2 =.07, 2 d.f., p < 0.2). However, the difference between, the 'better' town socio-economically, and, the 'worse' town socio-economically, is statistically significant ( 2 =.9, 1 d.f., p < 0.05). Table shows the answers to the question which sought to elicit a history of podagra by asking, 'Have you ever had an attack of extremely severe in either of your big toes which was not due to injury?' The period prevalence rates are about 70 higher than those in Table 2. The three towns are ranked in the same order with prevalences increasing from.7 in, to 7.7 in and 8. in. Again agestandardisation does not modify the rates. The differences between the three towns are statistically significant ( 2 = 7.09, 2 d.f., p < 0.05). The difference between and is likewise significant (X 2 = 7.01, 1 d.f., p< 0.01). If respondents are defined as of through a positive response to either of the two questions there are a total of 8 (272 from, 7 from, 275 from ). Age-specific prevalences based on these are shown in the Fig. The prevalences rise with age, as is seen in Tables 2 and and as would be Age Group 5^» Overall * From replies to question 'Have you ever had?'

3 THE PREVALENCE OF GOUT IN THREE ENGLISH TOWNS 7 TABLE Age-specific period prevalence of in the big toe* among men in the three towns Age Group Overall * From replies to question 'Have you ever had an attack of extremely severe in either of your big toes which was not due to injury.' expected because the rates are period rather than point prevalences. Within each age group the rates tend to follow the trend of the overall rates, rising from to to. However, at 5 years and over the rates fall. Analysis of three characteristics of in the big toe, as elicited by specific questions, showed little variation between the towns (Table ). About half the attacks of extremely severe in the big toe were said to have lasted for less than one week. About of men who had had attacks stated that there was always very rapid swelling of the toe during an attack. stated that there was peeling of the skin as the attack settled down. Using occupational information given by the respondents the social class distribution of men stating that they had had.was compared with that of. For this purpose two age-matched Prevalence () 10 from the same town were selected at random for each case of under the age of retirement. Occupational data of sufficient detail to enable social class coding were available for 255 of the 0 of this age. Use of matched eliminated the necessity of social class coding all the returned questionnaires. The results are shown in Table 5. There are no marked differences between the social class distributions of the and. Comparison of the duration of residence in the towns between the and revealed no difference. The mean years of residence for and combined were in, 5 in and 9 in. DISCUSSION This postal questionnaire survey has shown an apparent Age (years) FIG Age-specific period prevalence of in the three towns* * Defined by history of or in the toe.

4 7 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY TABLE Duration, occurrence of swelling and peeling of skin in attacks of extremely severe in the big toe Duration of a/lack < 1 week 1 week welling Present Absent Peeling of skin Yes No TOTAL 2 25 inverse relationship between the prevalence of and socio-economic status in three English towns. Gout was detected by answers to two questions a respondent's statement that he had had the disease or a history of extremely severe in the great toe. Answers to the first question could be influenced by the diagnostic practices of general practitioners, the attitudes of patients towards general practitioner consultations and patients' knowledge of the disease. Currie-* examined the clinical features of 9 of recorded by general practitioners throughout Britain and found no marked or systematic variations in diagnostic practice. To explain the findings of the present survey in terms of differences in patients' behaviour or knowledge it would be necessary to postulate either that patients with in a poor town are more willing to seek medical attention than those in a wealthy town, or that they are more willing to diagnose themselves as having without seeking medical advice. Answers to the second question depend on the patients' recollection of an attack of in the great toe. Information was also elicited about three character 1 istics of the whether the duration was less than one week, the occurrence of rapid swelling during the attack, and peeling of the skin during recovery. Initial 8 TABLE testing of the questionnaire suggested that these characteristics would enhance sensitivity and specificity. However, the replies of 78 patients who stated that they had had an attack of showed that only the occurrence of rapid swelling was closely associated with whether or not a patient stated that he had had the relationship being summarised by a sensitivity of 5 and a specificity of 78. Since the frequency of occurrence of the three characteristics is similar in all three towns inclusion or exclusion of patients according to their presence or absence would not alter the ranking of the towns in terms of rates. Neither of the two questions distinguishes primary from secondary but the latter, in the series reported by Currie, accounted for only 10 of. Although there are obvious disadvantages in the use of postal questionnaires to elicit diagnostic information the prevalences are based on a total of 10 reponses. Our finding of life-time period prevalences ranging from.9 to.8 in reply to the question 'have you ever had ' may be compared with the prevalence of 2.8 recorded in the Framingham survey of a similar age group of men. The higher rates in our survey could reflect either a higher incidence or over-reporting of the disease. However, using replies to either or both of the questions there Percentage social class distribution of * patients and age matched Social class 1 IN HIM IV V numbers ' Defined by history of.

5 is a progressive increase in the reported prevalence of from, the town of highest socio-economic status, through, to, which has the lowest socio-economic status. Despite reservations about use of the questionnaire to measure the absolute prevalence of we conclude that the differences between the towns do reflect differences in prevalence. These findings conflict with the concept of as a disease of affluence. This concept does not derive from the geographical distribution of the disease, for high prevalences have been recorded in populations in the Pacific Islands and among the Maoris in New Zealand, while there are low prevalences in some European countries, for example Finland and northern Holland. 1 Rather, studies have shown an association between and higher social class. In 2 Popert and Hewitt 8 found that out of 95 patients attending a clinic in Manchester, England, 1 were in social class 1 or 2. More recently a study of 97 patients from general practices scattered throughout Britain showed that a higher proportion were in social classes 1 and 2 than would be expected on the basis of national census data.' In a population study in New Haven, Connecticut, 200 people, comprising a sample stratified by socio-economic status, were interviewed. 5 gave a history of and the frequency with which was reported decreased progressively from 2.9 in social class 1 to 0.8 in social class 5.' However, in a recent study in Copenhagen it was found that 10 patients, identified by examination of a large sample of middle-aged men, had lower social status than 208 age-matched." In the present survey there was no difference between the social class distribution of people stating that they had had and age-matched from the same town (Table 5). Among respondents who gave a history of in the great toe associated with rapid swelling, but who stated that they had not had, there were who were under retirement age and gave sufficient occupational detail to enable social class classification. 5 () of them were in social class or 5 compared with 2 of age-matched. It could be argued that a patient will usually only know he has if he consults a doctor, and that many of these patients did in fact have but had not consulted their doctors. They therefore did not know the diagnosis. The disproportionate number of such people coming from social classes and 5 could suggest that general THE PREVALENCE OF GOUT IN THREE ENGLISH TOWNS 75 practitioner data on may be biased towards its diagnosis in the higher social classes. The magnitude of this possible bias cannot be determined from the findings of this survey. If it is small, and the findings shown in Table 5 reflect the actual social class distribution of, then the lack of any variation in prevalence with social class contrasts sharply with the variation according to the general socio-economic status of the towns. An inference is that there is a factor in the aetiology of which is more prevalent in a poor socio-economic environment but which, within that environment, does not preferentially affect people of lower social class. ACKNOWLEDGEMENTS We are grateful to A Laycock for his help in the design and validation of the questionnaire. We also thank the Family Practitioner Council Committees of Lancashire, Suffolk and, who allowed us access to their records. Mrs Sally Webber helped with the analysis of the data. The Department of Health and Social Security and Merck Sharp and Dohme Ltd gave financial assistance. REFERENCES 'Lawrence JS Rheumatism in populations. London: Heinemann Garrod A B. A treatise on and rheumatic (rheumatoid arthritis). London: Longmans-Green, 7. J Currie W J C. Prevalence and incidence of the diagnosis of in Great Britain. Ann Rheum Dis 79; 8: 101- Brochner-Mortensen K. Heberden oration 57:. Ann Rheum Dis 58; : Gardner M J. Using the environment to explain the predict mortality. Journal of the Royal Statistical Society (series A) 7;1:1^*0 Barker D J P, Gardner M J, Power C, Hutt M S R. Prevalence of gall stones at necropsy in nine British towns: a collaborative study. BrMedJ 79; 2: Hall H P, Barry P E, Dawber T R, McNamara P M. Epidemiology of and hyperuricaemia. AmJ Med 7; : Popert A J, Hewitt J V. Gout and hyperuricaemia in rural and urban populations. Ann Rheum Dis 2:21: - * Currie W J C. The patient in general practice. Rheum Rehab 78;: Acheson R M, O'Brien W M. In population studies of the rheumatic diseases (eds Bennett P H and Wood P H N). Amsterdam: Excerpta, Medica Foundation, 8. " De Muckadell O B S, Gyntelberg F. Occurrence of in Copenhagen males aged -59. Int J Epidemiol 7; 5: -58 (Revised version received 1 July 81)