Papers

Analysis of the sociodemography of gonorrhoea in Leeds, 1989-93

BMJ 1997; 314 doi: https://doi.org/10.1136/bmj.314.7096.1715 (Published 14 June 1997) Cite this as: BMJ 1997;314:1715
  1. Charles J N Lacey (c.lacey{at}ic.ac.uk), consultant physiciana,
  2. David W Merrick, statisticianb,
  3. David C Bensley, regional statisticianb,
  4. Ian Fairley, senior registrara
  1. a Department of Genitourinary Medicine, General Infirmary, Leeds LS1 3EX
  2. b Regional Public Health Analysis Unit, Northern and Yorkshire Regional Health Authority, Harrogate HG1 5AH
  1. Correspondence to: Dr C J N Lacey Department of Genitourinary Medicine and Communicable Diseases, Imperial College School of Medicine at St Mary's, London W2 1PG
  • Accepted 22 May 1997

Abstract

Objective: To investigate the epidemiology of gonorrhoea in an urban area in the United Kingdom.

Design: Analysis of all cases of gonorrhoea with regard to age, sex, ethnic group, and socioeconomic group with 1991 census data as a denominator.

Setting: Leeds, a comparatively large urban area (population around 700 000) in the United Kingdom.

Subjects: All residents of Leeds with culture proved cases of gonorrhoea during 1989-93.

Main outcome measure: Relative risk of gonorrhoea.

Results: Sex, age, race, and socioeconomic group and area of residence were all independently predictive of risk of infection. Young black men aged 20-29 were at highest risk, with incidences of 3-4% per year. Black subjects were 10 times more likely than white subjects to acquire infection, and subjects from the most deprived socioeconomic areas were more than four times more likely than those from the most affluent areas to acquire infection.

Conclusions: Different ethnic and socioeconomic groups vary in their risk of infection with gonorrhoea within an urban area. Targeted interventions and screening to reduce the incidence of sexually transmitted disease are now priorities.

Key messages

  • Ethnic group and socioeconomic group or area of residence are independent risk factors for gonorrhoea

  • Ethnic group and factors associated with neighbourhood of residence may modulate sexual risk factors through cultural and behavioural mechanisms

  • Sexual risk reduction and disease screening interventions targeted at groups at greater risk should now be evaluated

Introduction

Sexually transmitted diseases remain a major public health problem worldwide. In England sexual health was one of the key areas in the Health of the Nation strategy,1 and a target was set of reducing the incidence of gonorrhoea in 1990 of 61 new cases per 100 000 population by 20% in 1995.

Gonorrhoea was the first sexually transmitted disease in which the dynamics of transmission were studied in depth using mathematical models.2 3 These studies suggest the existence of core groups in maintaining the endemicity of gonorrhoea; these groups have higher incidences of infection and levels of sexual activity than the general population. The first empirical confirmation of such core group transmission was obtained by analysing the area of residence of people with gonorrhoea in upstate New York, and this showed an intense concentration in the inner city, relative risks for the central core area being 19.8 for men and 15.9 for women.4 Further data from the United States have shown young black men and women to be at increased risk of infection.5 6 In 1991 data on teenagers aged 15 to 19 in different regions of the United States showed that black men had a 73.3-fold increased risk compared with white men and black women a 23.3-fold increased risk compared with white women.6 To our knowledge, no analysis has determined whether these differences in risks are attributable to socioeconomic factors rather than ethnic group or a combination of both.

The 1991 census in the United Kingdom provided detailed information of the population and for the first time included data on ethnic group.7 We therefore studied the epidemiology of gonorrhoea within a defined large urban area, focusing on age, ethnic group, and socioeconomic variables.

Subjects and methods

We recorded details of all people resident within the boundaries of Leeds Health Authority who presented with culture confirmed gonorrhoea from 1 April 1989 to 30 September 1993 at this hospital, which is the only sexually transmitted disease clinic serving the Leeds city population of around 700 000 people. Patient information recorded included sex, age, date of birth, whether the gonorrhoea had been acquired heterosexually or homosexually, clinic number (used to identify people with recurrent episodes), and ethnic group. During the study ethnic group was assigned by reception staff using the Office of Population Censuses and Surveys' classification (this was replaced in 1995 by self assigned ethnic group). For the study analyses this classification was simplified to the categories white, black (includes black Caribbean, black African, black other), Asian (includes Indian, Pakistani, Bangladeshi, Chinese, Asian other), or other. All other microbiology laboratories and sexually transmitted disease clinics within a 20 km radius agreed to provide the same data for culture confirmed cases of gonorrhoea in people who were resident within the Leeds city boundaries and presented to their services.

We used the Super Profile classification as an indicator of socioeconomic status8 as this had been used to analyse morbidity and mortality in the population of Yorkshire.9 The Super Profile classification we used is a 10 cluster group classification of enumeration district areas of similar socioeconomic status on the basis of 120 census variables which are transformed using principal component analysis. The 10 socioeconomic categories are subsequently referred to as groups 1 to 10. Deprivation indices such as the Jarman, Townsend, and Carstairs indices are strongly correlated with Super Profiles (r =0.822, 0.867, 0.911 respectively).8 Postcodes were used to derive the socioeconomic group of patients on the basis of the enumeration district in which they lived. Denominators to calculate the incidence were taken from the 1991 census.

Analyses

Crude incidences and their exact asymmetric 95% confidence intervals were obtained by sex, age, race, and socioeconomic group using a method described by Miettinen.10

Logistic regression was used to model the incidence of infection using sex, age, race, and socioeconomic group as independent variables.11 12 Relative risks with 95% confidence intervals were used to measure the likelihood of infection associated with values of the independent variables, with white men aged 15-19 living in enumeration districts classed as socioeconomic group 1 as the reference group.

Results

Time series and number of episodes

Between 1 April 1989 and 30 September 1993, 1416 people presented with a total of 1664 gonococcal infections. Ninety seven per cent of cases were treated at the Leeds General Infirmary. Only 105 cases (6.3%) occurred in homosexual men, and these are included and not distinguished further in the analyses. During the study the incidence of gonorrhoea fell by 50%. This was found equally in men and women and in white and black subjects. The peak incidence of cases was always seen in the third quarter (July to September) of each year. The proportion of subjects with repeat infections was 29% (85/294) for black men, 19% (17/89) for black women, 10% (52/521) for white women, and 7% (32/491) for white men.

Crude incidences

The crude incidences of gonococcal infection by sex, age, ethnic group, and socioeconomic group are shown in table 1). Those under 15 years old, those over 55 years old, and those in socioeconomic group 2 are excluded from table 1) owing to small numbers. Men had a higher rate of infection than women–54.5 per 100 000 (95% confidence interval 50.8 to 58.4) compared with 38.5 per 100 000 (35.5 to 41.7) respectively. Peak incidences across the age distribution occurred in men aged 20-24 years (268.4 per 100 000) and women aged 15-19 (250.3 per 100 000). The most striking result from this preliminary analysis is that the overall incidence in black subjects was 793.4 per 100 000 (716.3 to 876.3). This is 22 times greater than the rate in white subjects and 62 times greater than that in Asians. All of these differences were significant (P<0.05).

Table 1

Incidence of gonorrhoea by sex, age, ethnic group, and socioeconomic group in Leeds, 1989-93

View this table:

Rates of infection varied significantly between socioeconomic groups. People living in areas that fell into the five most prosperous categories of this classification had similar and comparatively low rates of infection, ranging from 23.0 to 32.3 per 100 000 in men and from 17.3 to 21.1 per 100 000 in women. These more affluent areas generally lie outside Leeds city centre. The incidence of infection among people living in areas that were in the five most deprived groups of the socioeconomic classification had comparatively high rates of infection that varied considerably. Those living in areas classed as group 8 and group 10 had the highest rates of infection: 293.0 and 178.8 per 100 000 in men and 208.3 and 125.3 per 100 000 in women respectively. Typically, these neighbourhoods were inner city areas with high proportions of ethnic minority groups; nearly half of all Leeds's black and Asian populations live in group 8 enumeration districts.

Logistic regression

As the univariate analyses had suggested that sex, age, ethnic group, and socioeconomic group were all related to incidence these variables were used as predictors of incidence in a regression model. The best fitting model contained eight significant effects: all four variables of the first model plus the interactions of sex by age, age by socioeconomic status, age by ethnic group, and sex by ethnic group. The results of this model are shown in figure 1), which shows the relative risks of gonococcal infection by sex, age, and ethnic group for socioeconomic groups 1, 6, and 8. The sex by age by race patterns of risk that emerge for these three socioeconomic groups are similar, although the relative risks are different, with a greater than fourfold increased risk between the most affluent and most deprived socioeconomic groups. Indeed, results from a model not fully presented here suggest that, on average, after controlling for sex, age, and socioeconomic group, black subjects in Leeds were more than 10 times likely than white subjects and about 50 times more likely than Asian subjects to have had one or more episodes of gonorrhoea during the study.

Fig 1
Fig 1

Relative risks of gonococcal infection (with 95% confidence intervals) by sex, age, and ethnic group in socioeconomic groups 1,6, and 8 (ln scale)

In most age groups in all socioeconomic groups the risk of infection for Asian women was significantly lower than that for white women. Similarly, although not significantly, Asian men generally had lower rates of infection than white men. On average, after controlling for sex, age, and socioeconomic group, white subjects in Leeds were nearly five times more likely than Asians to have had one or more episodes of gonorrhoea during the four and a half years of the study.

Discussion

Risk factors for gonorrhoea

We found large variations in the incidence of gonorrhoea among different groups of subjects within a large city in the United Kingdom. We believe that the discrete urban area and the open access services to sexually transmitted disease clinics in the United Kingdom will have made our degree of case ascertainment high. Previous data from the United Kingdom have shown variations in the incidence of gonorrhoea with age, sex, and geography.13 14 15

We found extremely high rates of gonorrhoea among young black subjects, with black men aged 20-29 at the highest risk. Underenumeration in the 1991 census preferentially occurred among those aged 20-29 and also to a degree among black compared with white subjects. However, this is likely to reduce the relative risk for black compared with white people aged 20-29 by a factor of only 0.97-0.95.16 Observer assigned ethnic group may have misclassified people of mixed or other racial groups as black. Nevertheless, the incidences we found for black and white subjects and their respective differences are similar to published data from the United States.5 6

We looked for any independent contribution of socioeconomic group to risk of gonorrhoea–that is, independent of race and other factors. We used a validated method based on socioeconomic variables associated with small defined areas of residence. Although we clearly found that socioeconomic group as thus defined was an independent risk factor, this variable could represent an effect of social characteristics and networks within certain neighbourhoods.17 18 The free confidential services of sexually transmitted disease clinics in the United Kingdom mean that it is unlikely to be related to the availability of treatment. Figure 1) shows that differences in risk by ethnic group persist across all socioeconomic or residential groups and that the size of increased risk between least and most affluent is far smaller than for that of people from different ethnic groups. The final geographical outcome of these contributor risk factors (mapping studies not shown) show a more complex pattern than reported from the United States.4 5 17 Our use of small geographical units defined various areas with high and medium incidence of gonorrhoea across the city.

Cultural and behavioural mechanisms

Our analyses have allowed us to conclude that socioeconomic status is not the primary cause of variations in incidence associated with ethnic group. The national survey of sexual lifestyles in the United Kingdom showed that black men were significantly more likely than white or Asian men to report having their first sexual intercourse before the age of 16, but there was no significant difference between white, black, and Asian women.19 Univariate analysis in the same survey suggested that black men reported having a greater number of sexual partners than did white men (median 8 v 4 respectively), but the number of observations was small and multivariate analysis was not performed (A M Johnson, personal communication). Such differences were not observed between white and black women. Ethnic influences probably affect sexual behaviour through cultural or contextual mechan- isms,20 although there is a dearth of research on this subject. However, we suggest that the beliefs and sexual behaviour of young black men as a group mediate high levels of risk activity and gonococcal acquisition and transmission within defined communities.

Future research should focus on effective interventions to reduce risk behaviour and gonococcal transmission. Knowledge of the geographical distribution of infection within urban areas can enable targeted programmes and screening to be developed. Culturally appropriate interventions that decrease sexual activity risk behaviours in inner city populations have been described.21 22 Implementation of such programmes with evaluation of their medium term effects should now become a research priority.

Acknowledgments

We thank Drs Michael Waugh, Eric Monteiro, and Janet Wilson for permission to study their patients, and Drs Emile Morgan and Janette Clarke for providing data.

Funding: No external funding.

Conflict of interest: None.

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