| |
Decline in HIV incidence and injecting, but not in sexual risk behaviour, seen in drug users in Amsterdam: a 19-year prospective cohort study
|
| |
| |
AIDS: Volume 20(13) 22 August 2006 p 1771-1775
Lindenburg, Catharina EAa,*; Krol, Annekea,*; Smit, Colettea; Buster, Marcel CAa; Coutinho, Roel Ab,c; Prins, Mariaa,b
From the aHealth Service of Amsterdam, Cluster Infectious Diseases, Department of Research, Amsterdam
bDepartment of Human Retrovirology, Academic Medical Centre, University of Amsterdam, Amsterdam
cNational Institute for Public Health and the Environment, Center for Infectious Disease Control, Bilthoven, The Netherlands.
The present study investigated trends in HIV incidence and both injecting and sexual risk behaviours among HIV-negative drug users of the Amsterdam Cohort Study (ACS). The long follow-up time of this cohort enabled us to evaluate temporal changes in risk behaviour, in HIV incidence, and in HIV transmission routes since 1985. In addition, we evaluated changes in trends since the widespread use of HAART.
....the HIV incidence among drug users in the ACS has declined since 1985. Accompanied by a reduction in injecting drug use and needle sharing, this decline occurred despite continued sexual risk behaviour. At present, new HIV seroconversions are related mainly to unprotected heterosexual contacts. Therefore, HIV prevention programmes for drug users should pay specific attention to the importance of safe sex practices....
Abstract
Objective: To study temporal changes in HIV incidence, HIV transmission routes, and both injecting and sexual risk behaviour in the open Amsterdam Cohort Study (ACS) among drug users. Initiated in 1985, the ACS enables us to study changes in trends since HAART became widespread in 1996.
Methods: Person-time techniques were used to study the trend in HIV incidence among HIV-negative drug users. HIV transmission routes were determined using detailed standardised questionnaires. Trends in injecting and sexual risk behaviours were evaluated with a logistic regression model adjusted for correlations between visits of the same individual.
Results:
The 1315 HIV-negative individuals, of whom 93 seroconverted for HIV, yielded 6970 HIV-negative person-years of follow-up.
The HIV incidence was seven per 100 person-years in 1986 and varied between 0 and 0.5 per 100 person-years after 1999.
The odds ratio was 15.6 (95% confidence interval, 2.6-94.6) for HIV transmission through unprotected heterosexual contact versus injecting after 1996 compared with the period before.
Reports of both injecting and borrowing needles significantly declined over the period 1985-2004.
Reports of sexual risk behaviour and sexually transmitted infections at follow-up visits decreased before 1996, but not after 1996.
Conclusion: The HIV incidence among drug users in the ACS has declined since 1985. Accompanied by a reduction in injecting drug use and needle sharing, this decline occurred despite continued sexual risk behaviour. At present, new HIV seroconversions are related mainly to unprotected heterosexual contacts. Therefore, HIV prevention programmes for drug users should pay specific attention to the importance of safe sex practices.
Results
Study participants and demographics
Of the 1315 HIV-negative drug users, 63% were male and 77% were of European ethnicity. On ACS entry, the median calendar year was 1991 [interquartile range (IQR), 1987-1998] and the median age was 30 years (IQR, 26-35 years). After 6970 HIV-negative person-years of follow-up, 93 participants seroconverted for HIV and 135 individuals died. Per individual, the median number of visits within 6 months from the preceding visit was 6 (IQR, 1-16). On average, 90% of participants that visited the ACS a given calendar year returned the next year.
HIV incidence and HIV transmission routes
The HIV incidence was 7/100 person-years in 1986 [95% confidence interval (95% CI), 3-16], dropping to 2/100 person-years in 1995 (95% CI, 1-4) (see Fig. 1) and continued to decline thereafter. Since 1999, the HIV incidence has fluctuated between 0 and 0.5/100 person-years.
Due to missing data, 65 out of 93 HIV seroconverters were included in the analysis of HIV transmission routes. Before 1996, 50 were related to injecting risk behaviour and eight were related to unprotected heterosexual contact, whereas after 1996, these figures were two and five, respectively. After 1996, compared with the period before, the unadjusted OR was 15.6 (95% CI, 2.6-94.6) for HIV transmission through unprotected heterosexual contact.
Trends in risk behaviour
The proportion of visits at which injecting was reported declined from 57% in 1986 to 21% in 2004 (Fig. 1). Among injectors only, borrowing needles decreased from 47 to 9%(data not shown). After 1996, the decline in injecting became steeper than before this period (P < 0.05; Table 1). However, among injectors only, the decline in borrowing needles was less pronounced. Interestingly, before 1996, the use of needle exchange units increased significantly, whereas thereafter a significant decrease was found.
Trends in sexual risk behaviour differed in general profile from trends in injecting risk behaviour. Visits at which any unprotected sex was reported declined from 52% in 1990 to 40% in 1996, and remained stable thereafter. Over the period 1990-2004, unprotected sex with steady partners moderately declined from around 35 to 24% (data not shown). Evaluation of time trends before and after 1996 for unprotected sex with casual partners and while exchanging sex for money found them similar to trends for any unprotected sex; that is, no significant decline in risk behaviour occurred after 1996 (Table 1).
The proportion of follow-up visits at which STI were reported decreased from 17% in 1986 to 3% in 2004 (Fig. 1). A significant decline was found before 1996, after which STIs tended to increase slightly over time (Table 1). For STIs reported at study entry, the decline was only significant after 1996.
In order to investigate the role of selective loss to follow-up and changes in inclusion criteria over time, all analyses were repeated with exclusion of those who died during follow-up, those who visited the ACS only once and drug users under 30, leaving 721 participants available for this analysis. In addition, analyses were repeated including 2516 visits more than 6 months from the preceding visit (16% of 16 128 visits). Results were comparable with those above for all outcome variables (data not shown).
Discussion
We found a steep decline in HIV incidence in the drug user cohort in Amsterdam. After peaking at 7/100 person-years in 1986, the incidence varied between 0 and 0.5 per 100 person-years since 1999. This is comparable with the rate found by others in some West European countries [7,19-21] and The Netherlands [22], but lower than was recently observed in London [23]. Factors related to drug use that could explain this steep decline in HIV incidence in the ACS include a strong decline in injecting, which became even stronger after the introduction of HAART in 1996. Borrowing needles likewise declined in the whole study period, although this decline became less pronounced in the HAART era.
A declining trend in the use of needle exchange units was observed in our drug user cohort after 1996. This observation was accompanied by a reduction in the absolute number of exchanged needles per calendar year in Amsterdam, which peaked in 1992 with 1 100 000 whereas in 2002 approximately 350 000 needles were exchanged [24]. Since accessibility of needle exchange units remained similar over the years (personal communication, G. van Brussel) these findings confirm that injecting drug use in Amsterdam has become less popular over time. Moreover, in 1986, 54% of ACS participants reported any non-injecting use of hard drugs whereas this proportion was 83% in 2004 (data not shown). This could indicate a shift from injecting to non-injecting drug use. All these observations suggest that harm reduction models such as those implemented in Amsterdam do not have a stimulatory effect on injecting in drug users in Amsterdam. This is also supported by other studies that found acute hepatitis B (HBV) infections reduced among injecting drug users in Amsterdam over the period 1992-2003 [25]. Hepatitis C prevalence, among young drug users in our cohort, has likewise dropped between the periods 1985-1989 (83%) and 2000-2004 (14%) [26].
Cross-sectional studies from the 1990s found a potentially important role for sexual risk behaviour in HIV transmission among drug users [27] as did recent prospective studies [28]. Although numbers were small, our study confirms this role. The stable trends in sexual risk behaviour and a possible increase in STI after 1996 raises concern for continued sexual HIV transmission among drug users, underscoring the need for prevention measures that focus on sexual risk reduction in this group.
Other factors might have affected the HIV incidence as well. Even though HIV-positive drug users may have less access to HAART than MSM, a virological response in those who do receive it will leave them less infectious. On the other hand, HAART might increase the pool of HIV-infected drug users because of their prolonged survival. In contrast, now more than 20 years into the HIV epidemic, the majority of those with high-risk behaviour who became infected with HIV early in the epidemic have died.
Selection bias prevents generalizations of our study results to the whole Amsterdam drug-user population and we cannot exclude that a cohort effect might partially explain the observed decrease in HIV incidence and injecting behaviour. Another limitation is that data on risk behaviour were self-reported, and bias toward socially desirable answers could cause underestimation of the proportion engaged in risk behaviour.
Although the decline in injecting and sexual risk behaviour in our cohort started before 1996, that year was chosen as the change point for the trends as we were interested in evaluating risk behaviour since the introduction of HAART. Whether this introduction has a causal relationship to the observed trends in risk behaviour or whether they reflect more general trends could not be determined. Among HIV-positive drug users in the ACS, no causal relationship was found between the use of HAART and the observed decline in injecting risk behaviour [15]. In addition, a small decrease in sexual risk behaviour was demonstrated among those on HAART.
In conclusion, the HIV incidence among drug users in the ACS has declined since 1985. Accompanied by a reduction in injecting drug use and needle sharing, this decline occurred despite continued sexual risk behaviour. At present, new HIV seroconversions are related mainly to unprotected heterosexual contacts. Therefore, HIV prevention programmes for drug users should pay specific attention to the importance of safe sex practices.
|
|
| |
| |
|
|
|
