C. Hartgers, E.J.C. van Ameijden, J.A.R. van den Hoek, R.A. Coutinho
Public Health Reports 1992



A syringe exchange (SE) was set up in Amsterdam in 1984 to reduce the risk of hepatitis B and human immunodeficiency virus (HIV) infection among injecting drug users (IDUs)'. Since then, SEs have been installed in many countries2. The aim of the Amsterdam SE was to promote the one-time use of needles and syringes by making them available without charge and thus increasing their accessibility and by disseminating information about HIV risk. The thinking was that through increased access, sharing of injection equipment (and reuse of one's own equipment) would not be necessary and would become less prevalent. Prior to 1984, IDUs could obtain new injection equipment by buying it. This is still possible at pharmacies, some shops, and on the street in the red light district of the City 3,4.

The sharing of needles and syringes for injecting drugs ("needle sharing") has been found to be related to multiple drug use ,5,6, younger age7,8 homelessness9,10 cocaine use (including injecting)", injecting drug use by a regular partner9 or by peers12, drug craving1 3, little experience with injecting1 3, and frequency of injecting''. Both in Amsterdam and elsewhere, drug users who take advantage of SEs report lower levels of sharing than users who do not avail themselves of SEs2.8.14-16. Can this difference in fact be attributed to having better access to syringes? It also may be due to a better motivation for risk reduction or to other characteristics of those who attend SEs.

Results from another Amsterdam study 3,8 suggest that users who regularly exchange needles and syringes for new ones, when compared with other IDUs, inject more frequently, for a longer period, and are more often in contact with methadone programs. In the United Kingdom, SE clients were found to be especially older, longer-term injectors2. In the State of Washington in the United States,

clients were found more often to be frequent, long-term injectors1 6. These characteristics could act as confounders in the relation between SE participation and needle sharing.

Another important issue is the stability of behavior over time. In the United Kingdom, contrary to expectation, SE participation was found to be highly variable over time". To our knowledge, no studies have examined the stability of needle sharing. With good access to syringes, however, it can be expected that needle sharing is less regular than with bad access.

Our study focussed on one aspect of needle sharing: borrowing, that is injecting with needles or syringes, or both, that have been used by somebody else. Since only HIV seronegative IDUs are at risk of becoming infected through this behavior, this study was conducted among HIV-seronegative IDUs only.

The aim of the study was to determine, among both regular exchange users and others, specific groups at increased risk of borrowing, so further prevention efforts could be directed at them. Three hypotheses that were deemed relevant to this undertaking were examined. 1) Regular SE users, when compared with nonusers or irregular users, inject more frequently and over a longer period and use daily methadone more often, 2) Regular SE users borrow used needles and syringes less often than others, and 3) Regular SE use constitutes stable behavior among current IDUs, while borrowing is variable; borrowing is more variable among regular SE users than among other IDUs.



In 1985, an epidemiological study of HIV infection was implemented among drug users in Amsterdam. This ongoing cohortstudy18 -2 0 involves voluntary and confidential HIV-antibody testing and counselling, combined with an interview conducted by trained professionals using a standard demographic and behavioral questionnaire. Drug users either can participate once in the study or also take part in the follow-up study (in which study-visits are scheduled every 4 months). For follow-up visits, participants receive 25 Dutch guilders (approximately $13). Participants enroll mainly through methadone programs or through a clinic on sexually transmitted diseases for addicted prostitutes, at which methadone is provided by methadone program staff members. The HIV seroprevalence among IDUs in the study cohort appears to be slightly higher than among Amsterdam IDUs recruited "on the street" 2' and in methadone programs 22. Enzyme-linked immunosorbent assays (ELISAs) are used for HIV testing.

Confirmation of a positive specimen is performed by competitive ELISAs and by immuno blotting, following Centers for Disease Control criteria 23.

Our study concerned all 131 HIV-seronegative IDUs who were examined in the larger ongoing study between March 1989 and January 1990 (either at intake or at follow-up) and who reported having injected drugs in the 46 months preceding their visit. These visits are indicated as A and concern an intake visit for 47 IDUs (36%) and a follow-up visit (2nd-12th visit) for 84 IDUs (64%), with a mean of 4.4 months (standard deviation (s.d.) 1.3) between visit A and their previous visit. The consecutive return visit for 113 (86%) of these 131 IDUs between June 1989 and December 1990, with a mean of 4.8 months since visit A (s.d. 2.2), is hereafter indicated as visit B.

Variables and analysis

For our purposes, current behavior was defined as behavior in the 6 months preceding an intake visit or, for follow-up visits, in the months since the previous visit.

Hypotheses 1 and 2 were studied crosssectionally at visit A. To study hypothesis 1, it was determined whether "regular exchange use" that is, currently obtaining 90% or more of new needles and syringes at the SE, was associated with current frequency of injecting, duration of injecting, or current daily methadone use. The 90% criterion was chosen because it gave a more clear-cut division between the two subgroups (75 exchangers, mean 99%, median 100% versus 55 non-exchangers, mean 20%, median 0%) than the 100% criterion (65 exchangers, mean/median 100% versus 65 non-exchangers, mean 31%, median 10x6).

To study hypothesis 2, we first examined the relation between regular exchange use and "borrowing", that is, currently having injected at least once with a needle or syringe or both previously used by someone else. Second, we studied social and drug use indicators of borrowing drawn from previous research on determinants of needle sharing. Third, we studied the effect of regular exchange use on borrowing, while controlling for independent and significant indicators of borrowing and other potential confounders, including five demographic variables: sex, age, nationality, number of years living in Amsterdam - previously found as an independent predictor of HIV-serostatus1 8 - and kind of visit (intake versus follow-up) in the larger cohort-study, because less injecting risk behavior was found to be associated with follow-up visits compared with intake visits".

To study hypothesis 3, a longitudinal analysis was conducted by comparing behavior at visits A and B among persons who currently injected at both visits. Statistics include the x2 test of independence, the two-sample t-test, the MannWhitney (M-W) test for two independent samples, the Pearson correlation coefficient, and the Spearman rank order correlation coefficient; p-values less than 0.05 were considered significant. In multivariate analyses, logistic regression modelling was used to determine the independent and significant (with p<0.05) contribution of variables in indicating regular exchange use (hypothesis 1) and borrowing (hypothesis 2). The contribution of these variables in indicating outcome is expressed in odds ratios (ORs) and 95% confidence intervals (Cis).


Characteristics of the sample Because of missing data, the effective sam ple size at visit A per variable varies from 123 to 131. Percentages for variables were calculated based on the number of persons for whom data were available. The sample consisted of 80 male (61%) and 51 female (39%) HIV-seronegative IDUs, who have lived in Amsterdam for a mean of 12.4 years (s.d. 12.5). Their mean age was 31.4 years (s.d. 5.9, range 19-47). Of the 131, 86 (66%) were Dutch, 22 (17%) German and 23 (17%) were of another nationality. Of the total, 114 (87%) study participants had permanent housing, that is, they were not homeless and did not live in a squatted house, and 58 (44%) had a steady sexual partner, 30 of whom were current drug injectors. Currently working as a prostitute (for money) was reported by 41 IDUs (32%).

Table 1 presents duration of drug use. All 131 IDUs reported lifetime use, and 128 (98%) reported current use of heroin or morphine or both. Current daily methadone use was reported by 96 IDUs (73%), with a mean daily dose of 47 milligrams (s.d. 17.6). A history of borrowing needles or syringes was reported by 92 (74%) participants, and a history of being "clean" for at least one month, that is, not being opiate dependent outside an institution after becoming dependent, by 78 (60%), with the longest continuous period of non dependence 12.6 months on average.

With regard to current daily use of non injected drugs, those used most often were methadone (73%), benzodiazepines (23%), 5 or more glasses of alcohol daily (22%), and heroin (11%). On current daily use of injected drugs, 36 (27%) reported injecting heroin, 21 (16%) injected cocaine, 44 (34%) injected heroin together with cocaine ("speedball"), and 7 (5%) injected amphetamines. Frequent injecting, defined as more than once daily on average, was reported by 66 (50%); 35 (27%) reported injecting once daily on average, and 30 (23%) less than once daily. A total of 67 (51%) reported regular injecting, that is, every week. Regular injecting was positively related with frequent injecting (X 2=23.55, df=2, p=0.0001). The 117 IDUs (89%) who injected in the previous month reported a mean of 3.7 injections on injecting days in that previous month (s.d. 2.9, median 3, range 1-15), with the same needle used a mean of 1.8 times in general (s.d. 1.3, median 1, range 1-8).

Hypothesis 1: determinants of regular exchange use

Among 130 respondents, 75 (58%) were regu lar users of the syringe exchange. The number of years since first injection was not significantly different for regular exchange users (mean 10.8, s.d. 6.2) and other IDUs (mean 10.5, s.d. 6.5). The number of years injecting regularly was slightly different, however. Regular users of the exchange reported a mean of 8.8 years of injecting regularly (s.d. 6.2) versus 6.9 years (s.d. 5.6) among other IDUs (M-W test, p=0.10). Frequent injecting was reported by 48 (64%) of the regular exchange users, compared with 18 (33%) among the other IDUs (X 2 =19.5, df=2, p<0.0001). Daily methadone use was reported by 54 (72%) of the regular exchange users, versus 41 (75%) among the other IDUs (not significant).

In multivariate analysis, frequency of injection was the strongest indicator of regular exchange use, while duration of regular injecting contributed at a marginal level and daily methadone use not at all. With the first two variables in the model, the odds ratios of currently injecting more than once daily and of once daily, as compared to less than once daily, were 8.65 (CI=3.05-24.54) and 4.47 (CI=1.46-13.69), respectively. The odds ratio for number of years regularly injected (per year) was 1.07 (CI=1.00-1.14). Daily methadone use was not a confounder

Hypothesis 2: the effect of regular exchange use on borrowing

Of 125 respondents, 36 (29%) reported borrowing previously used needles or syringes or both. Of 30 borrowers about whom more data were available, 5 had borrowed exclusively from their steady sexual partner. Only one of these IDUs reported that this steady partner recently tested HIV-negative.

Of the 75 regular exchange users, 18 (24%) reported borrowing, while 18 (33%) of the other 55 IDUs did so (OR=0.63, CI=0.29-1.38). This difference is not statistically significant (X2=1.35, df=1, p=0.24). The figure shows this difference between regular exchange users and other IDUs corrected for frequency of injecting. There is no confounding or interaction. For 30 borrowers (15 regular exchange users, 15 other IDUs) more data on borrowing were known. Regular exchange users reported a median of 2 times borrowed (range 1-180), as compared with a median of 1 (range 1-10) among other IDUs (M-W test, p=0.52). Four regular exchange users (27%) reported disinfecting borrowed equipment (either with bleach or by boiling), as compared with 5 other IDUs (33%) (Fisher's exact test, p=1.0). Thus, with regard to borrowing and disinfecting, no significant differences between regular exchange users and other IDUs were found.

Reuse of one's own needle and syringe was different: 48 (66%) of the regular exchange users reported using the same needle only once, compared with 21 (38%) of the other IDUs (x 2=9.6, df=1, p=0.002).

Table 2 lists (next to five demographic variables) the examined social and drug use variables and their bivariate associations with borrowing. In multivariate analysis, the following three variables were independent and significant indicators of borrowing: (a) number of years with moderate-to- heavy alcohol use, (b) permanent housing, and (c) frequency of cocaine injecting. The model that resulted when regular exchange use was entered is shown in table 3. As can be seen, the adjusted OR for regular exchanging is 0.60, which is not statistically significant, and not different from the bivariate relation.

Duration of injecting, daily methadone use, and demographic variables were no confounders for the effect of regular exchange use on borrowing. Frequency of injecting was found to be a slight confounder. When entered into the model in table 3, the adjusted OR for regular exchange use became 0.49 (CI=0.18-1.31). The interaction term of frequency of injecting and regular exchange use did not improve the model.



Hypothesis 3: is regular exchange use a stable habit and borrowing not?

Among the 113 IDUs seen at visit B, 5 had seroconverted since visit A. This corresponds to a seroconversion rate of 11.0 per 100 person-years (CI=0.62-19.18).

Among the 113 IDUs, 101 reported current injecting. Borrowing since A was reported by 22 of these 101 current injectors (22%), and regular exchange use by 69 (68%). In a longitudinal analysis, among the 101 who were current injectors at both visits A and B, regular exchange use at A was related to regular exchange use at B (Pearson's r=+0.45, p<0.001, n=100): of regular exchange users at A, 84% is again a regular exchange user at B.

Borrowing at A is related to borrowing at B (r= +0.32), p<0.01, n=93): of borrowers at A, 42% report borrowing at B, while among non borrowers at A only 13% report borrowing at B. The relation between borrowing at A and at B was different for regular exchange users and other IDUs, although contrary to our hypothesis. Among regular exchange users at A, a strong relation between borrowing at A and B was found (r= +0.63, p<0.001): of the IDUs who reported borrowing at A, 62% also reported borrowing at B, compared with 4% among those not reporting borrowing at A. No significant relation was found among the IDUs who did not regularly exchange: r=-0.11 (23% of borrowers at A and 33% of non borrowers at A reported borrowing at B). The strong positive relation between borrowing at A and B among regular exchange users, and the absence of such a relation among other IDUs, was also found after controlling for frequency of injecting.


One of the main findings of our study was that regular exchange use may be attributable to differences in drug use. Similar to earlier finding8, the Amsterdam SE seems most attractive to frequent, long-term injectors. In our sample, no indications were found that daily methadone users were regular SE clients more often than other IDUs.

Before further discussion of our findings, we would like to reiterate that the sample consisted of HIV-seronegative IDUs only, that is, IDUs at risk of HIV infection. Many studies of determinants of needle sharing concern IDUs with unknown serostatuss 5, 12. Comparisons of results, therefore, need to be made cautiously. The self-reported data may be biased by memory loss or a tendency to give socially desirable answers. Also, the sample consisted of volunteers for an HIV test that was combined with an epidemiological study of HIV. Therefore, one should be careful in generalizing findings to the population of HIV-negative IDUs in Amsterdam.

Although 74% of the IDUs in the sample had a history of borrowing, they remained seronegative so far. Nevertheless, it is not a "safe" group, as indicated by the seroconversion rate found at follow-up. Groups at increased risk of borrowing were long-term moderate-to-heavy alcohol users, current cocaine injectors, and persons without permanent housing. When examining the interrelations between the long-term drug use variables, the numbers of years of alcohol use is most strongly related to years of tranquillize use (Spearman's r- +0.48). The alcohol variable thus reflects a history of alcoholism or polydrug use or both in addition to the primary opiate addiction. Polydrug use has been found related to needle sharing 5 ,6 as have homelessness 9,10 and cocaine use (including cocaine injecting)',' 11,24,25. Regular exchange users were found to borrow less often than other IDUs for each category of frequency of injecting. This relation was not statistically significant, however, even after controlling for other potential confounders.

Regular exchange use was a rather consistent behavioral characteristic over an average period of 5 months. This suggests that client turnover is a smaller problem than in the United Kingdom". It is difficult to compare findings, however, because of differences in study design and measures. Contrary to our hypothesis, borrowing seems to be especially regular among the group of regular exchange users, while it is more variable over time among other IDUs. This finding could not be explained by differences in frequency of injecting. Thus, another group at increased risk of borrowing are previous borrowers, especially among regular exchange users.

What are the implications of our findings for further prevention efforts? The absence of "hard" indications for a lower level of borrowing among regular exchange users is in line with the results of other studies among IDUs participating in the cohort-study 19,20,26 In our view, however, this does not necessarily lead to the conclusion that the Amsterdam SE has no preventive effect.

First, if IDUs with a relatively high risk level participate in the cohort- study 21,22 this may obscure the differences between regular exchange users and other IDUs with regard to borrowing. Also, the differences in borrowing between regular exchange users and other IDUs may reflect a real difference in the population that may not have reached statistical significance in our study because of the small sample size. Second, we found that regular exchange users reuse their own needles and syringes less often than other IDUs, which may indicate better access to syringes. Third, we found that borrowing - as well as not borrowing - is particularly consistent among regular users of the exchange. At the outset, we assumed that regularity of borrowing is indicative of the degree of access to syringes. This finding would thus lead to the unlikely conclusion that regular exchange users have less access to syringes than other IDUs. A better explanation may be that borrowing (and not borrowing) among regular exchange users is dependent on certain individual characteristics, while for other IDUs - among whom borrowing behavior was not consistent over time - it is more situationally determined. Since regular exchange users more often are frequent, long-term injectors, they may possess other individual characteristics, such as psychopathology", presently not measured, that may confound the effect of regular exchanging on borrowing. Fourth, there may be a time effect. A study in the United Kingdom , compared sharing behavior of users and nonusers of SEs from 1987 to 1990. Sharing declined in both groups, but it did so most strongly among nonusers of SEs. While nonusers of SEs had higher levels of sharing than SE-users in 1987, this difference had almost disappeared in 1990. There are indications of a similar development in Amsterdam26 Thus, in 198485, the SE may have attracted risk reduction motivated IDUs, while five years later, a motivation for risk reduction may be equally present among regular exchange users and other IDUs. Our findings suggest that IDUs with different injecting behavior find different ways to supply themselves with new syringes according to their needs. Financial motives, for example, may induce infrequent injectors to buy syringes and frequent injectors to exchange them. If the degree of access to syringes, according to one's needs, and the degree of motivation for risk reduction is similar among regular exchange users and others, then regular SE participation, compared with irregular participation or none at all, should not be expected to have a direct effect on borrowing. Therefore, factors like degree of access to new syringes (in relation to the amount needed) and motivation for risk reduction should be take into account in studies of SE users and nonusers and in studies of seroconversion-rates among these groups. Furthermore, results from studies of SEs in countries where new syringes can be purchased relatively easily (like the United Kingdom and the Netherlands) and access is relatively good cannot be generalized to countries (like the United States) where buying injection equipment is illegal and access is relatively bad.

With these caveats in mind, the question is which prevention efforts might help to reduce the risk behavior we have found. In our view, it seems more important to direct additional preventive measures at IDUs with an increased risk of borrowing than at IDUs participating in the SE irregularly or not at all. Three groups at increased risk of borrowing (cocaine injectors, long-term alcohol users, and IDUs without permanent housing) may have in common difficulties with advance planning and with keeping adequate supplies of new syringes. In that case, increased access to syringes, through extending opening hours at locations where syringes can be bought or exchanged, and through increasing the number of such locations, may be helpful. If the major obstacle is the carrying of new syringes, however, then provision of small bottles of bleach seems an adequate measure, provided that IDUs do not have the same objections against carrying bleach.


This study was supported by the Netherlands foundation for Preventive Medicine (grant no. 28-1258).

The authors are grateful to B. Frdlich, B. Scheeringa-Troost, and R. Lopes Diaz for interviewing and collecting blood samples, to Dr. J. Goudsmit and M. Bakker for performing the laboratory tests, and to H.J.A. van Haastrecht for data management.


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