In 2002, an estimated 49 500 individuals in the United Kingdom were living with HIV infection, 31% of whom were undiagnosed . In England, a goal of the National Strategy for Sexual Health and HIV  is to reduce the prevalence of undiagnosed HIV infection by 50% within the next 4 years. The implementation of the strategy has encouraged the promotion of HIV testing at sexually transmitted disease (STD) clinics in addition to well-established antenatal and blood donation screening programmes. A further refinement of the strategy to encourage the uptake of HIV testing, especially among men who have sex with men (MSM) has been identified as a priority by the Chief Medical Officer (England) .
The motivation behind HIV testing is complex, and an individual's decision to be tested may be affected by a range of factors including HIV testing policy, the effectiveness and availability of medication, the availability of testing, and health education messages promoting HIV testing. Studies have shown that HIV testing is common among MSM, ranging from 37–64% in the UK [4–8] to 83–85% in Australia [9,10], 63% in Canada , and 84% in the United States [12,13]. Previous studies, including both general population probability sample and convenience sample studies undertaken in community, STD clinic and HIV testing clinic settings in the United Kingdom, have shown strong associations between HIV testing uptake and high-risk sexual behaviours in both MSM and heterosexual individuals [4,6,7,14,15]. However there are no current estimates of the prevalence of HIV testing in the general population in Britain. In this paper we report population estimates of HIV testing patterns and associated behaviours from the second British National Survey of Sexual Attitudes and Lifestyles (Natsal 2000).
Participants and survey methodology
Natsal 2000 and its additional ethnic minority boost sample is a stratified probability sample survey of the general population of 12110 men and women aged 16–44 years resident in Britain. The study was undertaken between 1999 and 2001, and the response rate was 65.4%. Participants were interviewed using a combination of computer-assisted face-to-face interview and computer-assisted self-interview for collecting more sensitive questions including questions on HIV testing. The methodological details and outcomes related to high-risk behaviours have been reported elsewhere [16–18]. In addition to a range of questions on sexual practices, behaviours and attitudes, we asked all respondents about their HIV testing history (if they had ever had a blood test that involved testing for HIV and when the last test was), the reasons for HIV testing, as well as the self-perception of personal risk of being infected with HIV.
Data from targeted over-sampling of ethnic minorities (the Natsal ethnic minority boost) were combined with the main survey data to increase the numbers of respondents included in this analysis. Natsal 2000 data were weighted to account for differential selection probabilities in the survey, and then post-stratified to British population estimates of the age, sex and region distribution from mid-1999, as previously described [16–18]. Odds ratios were used to measure the association of behavioural, demographic and risk perception factors with reporting a voluntary HIV test in the past 5 years, i.e. excluding HIV testing through blood donation and antenatal screening. Logistic regression analyses were used to calculate adjusted odds ratios (AOR), to identify factors independently associated with HIV testing in this time frame. We performed all analyses using the survey analysis software Stata (version 8.0; Stata Corp., College Station, TX, USA), accounting for stratification, clustering and weighting of the sample.
The study was approved by the University College Hospital and North Thames Multi-Centre Research Ethics Committee and all the Local Ethics Committees in Britain.
Prevalence of and reason for HIV testing
Overall, 32.4% [95% confidence interval (CI) 30.8–34.1] of men and 31.7% (95% CI 30.5–33.0) of women reported ever having had an HIV test (Table 1). Just under a quarter reported an HIV test in the past 5 years: 23.8% (95% CI 22.3–25.2) of men and 23.5% (95% CI 22.3–24.7) of women. The majority of both men and women were tested through blood donation, whereas 16.5% of women who had ever been tested, and 17.0% who had been tested in the past 5 years, reported pregnancy as the main reason for their last HIV test (Table 1). A greater proportion of men reported both a ‘general health check’ and ‘concern of risk to self’ as a reason for their last HIV test than women, both ever and in the past 5 years. These reasons accounted for a quarter of all HIV tests in men, although because men are not routinely screened as a result of pregnancy these differences are expected.
As both antenatal screening for HIV (pregnancy given as the main reason for an HIV test in women) and blood donation constitute screening programmes rather than individuals choosing to be tested for HIV, blood donation and antenatal screening were excluded from further analyses of demographic and behavioural factors associated with voluntary confidential HIV testing (VCT). Table 1 shows the prevalence of VCT in the past 5 years, with adjusted odds ratios (AOR) associated with having an HIV test by demographic, social and behaviour variables. Overall, 9.0% (95% CI 8.1–10.0) of men and a significantly lower proportion of women, 4.6% (95% CI 4.0–5.2), chose to have an HIV test in the past 5 years.
In univariate analysis having an HIV test in the past 5 years was associated with being aged 25–34 years and being of a higher social class in men, and living in Greater London, not having been married, and being black Caribbean, black African, and of other ethnicity for men and women. Greater numbers of sexual partners, reporting a previous sexually transmitted infection (STI), acquiring new sexual partners from abroad, and increasing numbers of same-sex partners were all associated with HIV testing in the past 5 years for both men and women. Nearly one third of injecting drug users had had an HIV test in the past 5 years.
In multivariable analysis, after adjustment for all demographic and behavioural variables, the demographic variables remaining statistically associated with having had an HIV test in the past 5 years were similar for both men and women. Men aged 25 years and over were more likely to have been tested than men aged under 25 years, whereas there was no difference in testing by age for women. Individuals living in Greater London had a significantly greater AOR of having had an HIV test compared with those resident in the rest of Britain (AOR 1.58 for men and 1.79 for women). The odds of HIV testing varied by ethnicity even after adjustment, with men of black African and ‘other’ ethnicity more likely to be tested compared with white men (AOR 3.45 and 2.51), whereas in women there was no difference, after adjustment (Table 2).
In multivariable analysis, after controlling for demographic and other behaviour variables, the magnitude of the associations of HIV testing with each behavioural variable reduced, but a significant association remained. The likelihood of having had an HIV test in the past 5 years increased with increasing numbers of sexual partners. Women who had had 10 or more sexual partners in the past 5 years, had an AOR of 4.15 of reporting an HIV test, compared with women who had had at most one partner, whereas men with 10 or more sexual partners had an AOR of 2.30. Acquiring new sexual partners abroad was also independently associated with HIV testing in the past 5 years, as well as reported STI in the past 5 years and injecting drug use for both men and women. Men who reported having more than 10 male sexual partners in the past 5 years had an AOR of 5.08 of having an HIV test compared with men who had no male partners.
Time since last HIV test and perception of risk
The prevalence of reported HIV testing varied according to an individual's perception of their self-perceived risk of HIV infection (Table 3). The prevalence of HIV testing was greater in all men who stated that they were ‘not very much at risk’ or ‘greatly or quite a lot at risk’ compared with those who perceived that they were ‘not at risk at all’ after adjustment for age (P < 0.0001). In women, the prevalence of testing by self-perceived risk was also greater in those who perceived themselves to be at a greater risk after adjustment for age. Both men and women who reported that they ‘don’t know’ if they were at risk of HIV infection were more likely to have had an HIV test than those who reported that they were ‘not at risk at all’. There was no difference in the prevalence of HIV testing in MSM by risk perception (P = 0.6385), although one third of men who had same-sex partners had been tested in the past 5 years.
Over half the respondents who reported choosing to have an HIV test in the past 5 years (i.e. excluding blood donation and antenatal screening) tested within the past 2 years; 28.3% (95% CI 23.8–33.3) of men and 25.4% (95% CI 20.2–31.4) of women reported their last HIV test in the past year, and 25.7% (95% CI 21.4–30.5) and 25.9% (95% CI 20.8–31.8), respectively, between one and 2 years ago. Among MSM, two thirds tested within the past 2 years; 37.8% (95% CI 24.7–53.0) in the past year and 28.6% (95% CI 16.5–44.8) between one and 2 years ago.
Place of last HIV test
The most commonly reported place where an HIV test was carried out was at an STD clinic for women (44.0%) and men (34.1%). General practice was also commonly reported for men (28.5%) and women (20.0%) (Table 4). Twenty per cent of men and women had had an HIV test ‘somewhere else’. The majority of MSM (52.0%) had had their HIV test at an STD clinic, whereas 18.4% reported that their last HIV test was at a general practitioner's surgery.
Natsal 2000, a national probability sample survey, provides estimates of the prevalence of HIV testing in the general population, and has found that overall over a third of British men and women have tested for HIV in their lifetime, the majority of whom have been tested through blood donation. When HIV screening through blood donation and pregnancy are excluded, testing for HIV in the past 5 years was associated with high-risk behaviours in both men and women. We also found reported HIV testing to be associated with certain demographic characteristics, including older age, residence in London, and black-African ethnicity. These may reflect both lifetime opportunity for HIV testing, self-perceived risk of HIV infection, and individual attitudes towards HIV testing. With the exception of older age, many of these characteristics are also associated with a greater burden of STI [1,17] and an increased likelihood of attending an STD clinic.
Robust prevalence estimates of HIV testing uptake in the general population are not available in many countries. In the USA, the general population prevalence of HIV testing was greater at 45.6%, whereas this excluded blood donors, it included testing through other screening programmes such as military service, immigration, marriage licence and occupational exposure, which together accounted for 45.2% of all HIV tests in men and 27.8% in women . Canadian estimates of general population voluntary HIV testing are also greater than the UK, at 17.8% of men and 15.6% of women . Convenience samples of MSM in the UK have reported greater rates of HIV testing, ranging between 53–64% ever tested [5,21] and 32% in the past year . However, of the MSM in our study who reported that they had had an HIV test in the past 5 years, a similar proportion reported an HIV test in the past year (36%). MSM recruited through Natsal include both MSM at higher and lower behavioural risk, as Natsal is a probability survey of the general population. In contrast, convenience sample surveys may be sampling men with higher risk behaviours. Nonetheless, the proportion of those MSM from Natsal 2000 who had attended an STD clinic in the past 5 years and had also had an HIV test has been found to be similar to other studies at 74% . Geographical differences in the prevalence of voluntary HIV testing in both MSM and the general population have been reported in the USA , Canada , and Australia . These have been associated with the differential availability of testing and service provision, and community attachment among MSM [10,11]. Unprotected anal intercourse, and HIV-positive partners were also found to be associated with HIV testing in MSM, and those who were at greatest risk were more likely to have been tested .
Our study has some limitations, as non-respondents may be different from those who chose to participate; however, the direction of this bias is unknown. Probability sample surveys, by their nature, do not achieve large samples of high-risk populations, although this was addressed in this survey through oversampling in London, and the focussed enumeration of ethnic minorities to achieve larger sample sizes in these groups, which were then weighted to correct for unequal selection probabilities. As both HIV testing and sexual behaviours were self-reported in Natsal 2000, this may lead to bias because of individual's reluctance to disclose sensitive behaviours. However, the cognitive interviews carried out to validate the methodology for Natsal 2000 concluded that individuals were happy to report their HIV testing behaviours, and as the respondent's HIV status was not requested, this subject was not considered to be too intrusive . Improved data collection methodology in 2000 with the use of computer-assisted self-interview (CASI) may have further facilitated the reporting of sensitive behaviours, including HIV testing. Comparisons of age-related cohorts between the 1990 and 2000 surveys indicated that it is possible that there has been a change in the willingness to report some experiences, perhaps in particular for those that are most socially sensitive . Because HIV status was not collected in our survey, the reported self-perception of risk could be informed by an individual's knowledge of his or her own HIV status. This appears to be more important in MSM as there was no evidence of a difference in the likelihood of reporting an HIV test in the past 5 years in those who did not perceive themselves to be at risk of HIV infection. However, in all men and women, the probability of reporting an HIV test in the past 5 years was greater in those who perceived themselves to be at risk or did not know if they were at risk.
HIV testing was associated with higher risk behaviours and numbers of sexual partners, and the numbers of same-sex partners for men. This suggests that HIV testing largely remains part of a reasoned decision-making process both on the part of the individual and their health service providers. Although HIV testing was associated with risk behaviours, and reporting STI diagnoses, the opportunities to offer and recommend HIV testing to those at increased risk of infection should be encouraged. A substantial number of HIV tests were reported to have taken place outside the STD clinic setting. If barriers to HIV testing exist, further research is needed to understand what they are and if they are with the provider or the individual. Voluntary confidential HIV testing is an important strategy for facilitating the management of HIV infection in the individual and reducing the likelihood of onward transmission through behavioural change and decreased viral load through antiretroviral treatment. National standards for HIV testing have been set in the National Strategy for Sexual Health and HIV , including an increase in the offer and uptake of HIV and STI testing. In order to decrease undiagnosed HIV infections, care should also be taken to ensure that HIV testing is available to all.
The study was supported by a grant from the Medical Research Council with funds from the Department of Health, the Scottish Executive and the National Assembly for Wales.
The authors would like to thank all the study participants, the team of interviewers and the operations and computing staff from the National Centre for Social Research who carried out the interviews.
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