HIV AND INJECTING DRUG USERS: THE ROLE OF PROTECTION MOTIVATION
C. Hartgers, P. Krijnen, J. van der Pligt

INTRODUCTION

Sharing of needles and syringes by injecting drug users (IDUs) carries a risk of acquiring or transmitting Human Immunodeficiency Virus (HIV) infection (Friedland, Harris, ButkusSmall et al. 1985, Robertson, Bucknall, Welsby et al., 1986, Chaisson, Moss, Onishi et al. 1987). Studies of "needle sharing" have focused mainly on demographic (e.g., age, sex), social (e.g. homelessness, having an injecting sexual partner) or drug use characteristics of sharers, and less on cognitive and motivational characteristics. For HIV-negative IDUs, aware of their serostatus, the motivation to protect themselves against HIV may contribute to safe behavior, while for HIV-positive IDUs, the motivation to protect others from acquiring HIV, as well as the wish to postpone AIDS by avoiding (re)infection, may contribute to not sharing equipment. In this study we will focus on cognitive and motivational antecedents of "borrowing" (i.e., injecting with a needle and syringe which has been used before by someone else) among IDUs who are not (yet) HIV-infected and who are aware of their serostatus.

Protection Motivation theory (Rogers 1983), the theoretical framework in the present study, has been applied to smoking behavior (Rogers, Deckner & Mewborn 1978), alcohol use (Kleinot & Rogers 1982), exercising (Wurtele & Maddux 1987), dental hygiene (Beck & Lund 1981), breast self-examination (Rippetoe & Rogers 1987) and AIDS (Van der Velde & van der Pligt 1991). The theory holds that information about a health threat evokes two cognitive processes: threat appraisal and coping appraisal (see figure 1).



According to the model, a maladaptive response like borrowing is facilitated by certain rewards (e.g. stopping drug craving while no sterile needle and syringe is available) and inhibited by the perceived severity of HIV infection and one's perceived vulnerability to it. In the model, anxiety has no direct relation with behavioral intention or behavior, but is mediated by perceived vulnerability, which is seen as a cognitive representation of anxiety. Adaptive responses, such as using new, one's own, or properly disinfected needles and syringes, are, according to the model, facilitated by response efficacy and self-efficacy. In the present context, response efficacy refers to the belief that using only new or one's own needles and syringes reduces the risk to acquire HIV. Self-efficacy refers to the perceived ability to perform these behaviors consistently. The costs of safe injecting, like having to buy new equipment, are expected to inhibit adaptive behavior. Figure 1 summarizes the relation between these facilitating and inhibiting factors, protection motivation and behavior. Two major methods of HIV prevention among IDUs are health education and provision of means. Health education provides information about the risk to get HIV-infected through needle sharing. Protection motivation theory holds that perceived vulnerability will inhibit maladaptive behavior. However, it also includes the possibility of interaction between threat and coping appraisal. If the perceived risk or severity is high, while one feels unable to protect oneself (i.e. has low response efficacy and/or self-efficacy), this may result, through feelings of helplessness and lack of control, in an adverse effect on behavior. Rogers (1983, p. 171) suggested: "These feelings may motivate attempts to restore perceived control of one's fate, which can be accomplished by consciously and vigorously choosing to perform the behavior that will lead to the inescapable danger." Increased feelings of vulnerability were indeed found associated with hopelessness (Rippetoe & Rogers 1987). Joseph et al. (1987) found that homosexual men believing to be at high HIV risk were less likely to undertake behavioral risk reduction than homosexual men with a low perceived risk. Furthermore, a high risk perception was associated with psychological and social distress.

Weinstein (1989) suggests that not only the perception of one's own risk (i.e., perceived vulnerability) is important in predicting behavior, but also comparative risk judgments. He used the term "unrealistic optimism" to describe biased perceptions of personal vulnerability to a health threat: people tend to think that they run less risk than others, while this is in fact not the case (Weinstein 1980, 1982, 1984). Unrealistic optimism may lead to the belief that additional precautions are unnecessary. It is unknown to which extent an optimistic bias is present among IDUs, and, if present, whether it contributes to unsafe behavior. Unrealistic optimism has been related to a variety of possible causes, both cognitive and motivational (see for a review van der Pligt et al, in press). One cognitive explanation sees optimism as the result of over reliance on past experience to predict the future and may be of relevance for HIV-negative injectors. Most HIV negative injectors have engaged in unsafe injecting during their life as an addict (Hartgers et al. in press), and have not yet become infected, while many of their peers have. This may lead to an optimistic judgment of risk and a low perceived vulnerability. Another cognitive explanation sees optimism as a function of perceived behavioral control: the higher the control, the more optimism. A motivational explanation sees exaggerated perceptions of control and unrealistic optimism both as defensive coping strategies, employed to protect oneself - through denial - against the anxiety raised by severe health threats. Thus, a higher perceived severity would be associated with more optimism, and optimists would experience less anxiety. Van der Pligt et al. (in press) suggest that defensive coping as origin of optimism may play a role especially among high risk groups.

The second major method of HIV prevention among IDUs is the provision of means. Programs include the provision of needles and syringes through exchange schemes (mainly in Europe), or the provision of bleach through outreach-workers to disinfect equipment before sharing (mainly in the U.S.). Participation in the needle and syringe exchange program will be considered as a potential behavioral determinant of borrowing in the present study. The Amsterdam syringe exchange, which started in 1984, aims to promote one time use of injection equipment by increasing (free) access to needles and syringes and by providing information about HIV risk. In 1991, one million new needles and syringes were handed out (personal communication, A.D. Verster, Municipal Health Service), while the population of current injectors in Amsterdam is estimated at around 2500 (Buning 1990). Before 1984, IDUs could legally buy new injection equipment. This option is still available: through pharmacies and certain shops (Hartgers et al. 1988, Van Santen 1990). Reasons for participation in the exchange program may vary. Next to a motivation to reduce risks, financial motives may be important (Hartgers et al., in press). Also, it seems likely that the exchange program does not appeal to IDUs who are in a stopping or starting phase of injecting (Hartgers et al. 1989). Since financial barriers fall away for participants of the exchange program, we expect that participation in this program decreases response costs, and thereby improves actual behavioral control (Ajzen 1991) and facilitates adaptive behavior. Both in Amsterdam and elsewhere, syringe exchange attenders have reported lower levels of sharing than non-attenders (Stimson 1989, Hartgers et al. 1989, Watters et al. 1991, Brettle 1991 and Hagan et al 1991).

In addition to actual behavioral control, it is important whether a person perceives to be in control of his or her behavior. The concept of "perceived behavioral control", which is related to self-efficacy (Bandura 1977), was added by Ajzen & Madden (1986) to the theory of "reasoned action" (Fishbein &Ajzen 1975). In protection motivation theory, self efficacy is only related to intention, while according to Ajzen & Madden (1986), "perceived behavioral control" is related to both intention and behavior. Since 1977, many studies have linked self-efficacy to health promoting and health-impairing behavior (Bandura 1986, Strecher et al. 1986). A cross sectional study among IDUs (Paulussen et al. 1990) confirms this: self-efficacy was found strongly related to both behavior and intention.

Finally, we will consider previous behavior as a potential determinant of borrowing. Previous behavior has been found related to future behavior independent of the regulating effects of behavioral intention (Bentley & Speckart 1979, Van der Velde, Hooykaas & van der Pligt, in press, Cleary et al. 1991). This effect may partly be attributable to method variance shared by the measures of prior and later behavior. However, if past behavior has a significant residual effect on later behavior, next to cognitive factors, this would indicate that an important factor (for example, habit) is missing in the tested model (see Ajzen 1991). Habit may be of importance as the investigated behavior - borrowing - is closely related to addictive behavior, which is in general characterized by compulsiveness and a long history.

The purpose of the present study is to investigate whether it is meaningful to study Protection Motivation in the prediction of needle sharing by IDUs. Other factors which will be considered are unrealistic optimism, participation in the syringe exchange program and previous behavior. As mentioned before, the present study concerns only IDUs who are not infected with HIV; all were aware of their negative serostatus through one or more previous HIV test(s). First, in a cross-sectional analysis, we will investigate the relations between previous borrowing, the different protection motivation factors and optimism. Second, we will study the relations between the different potential behavioral determinants and borrowing at follow-up. The implications of our findings for HIV prevention programs among IDUs will be discussed.

METHOD

Subjects

The present data set is part of a longitudinal study of HIV infection among drug users (DUs) in Amsterdam which started in 1985. This ongoing cohort-study (e.g. Van den Hoek et al. 1988, Van Haastrecht et al 1991) involves voluntary and confidential HIV-antibody testing and counselling for DUs, combined with an interview conducted by trained professionals using a standard questionnaire (in Dutch, English or German). Most DUs in the cohort-study enroll either through methadone programs or through a Sexually Transmitted Diseases (STD) clinic for addicted prostitutes. Subjects can participate only once or take part in the follow-up study. In this study, visits (including HIV testing) are scheduled every 4 months, and participants report on current behavior, i.e. behavior since their previous visit. For each follow-up visit, DUs receive 25 Dutch guilders (approximately $13). Enzyme-linked immunosorbent assays (ELISA's) and/or immunoblotting are used for HIV testing (see Van den Hoek et al., 1988).

In the period June-December 1990, 245 participants who assumed to be HIV-negative on the basis of previous test-result(s) came for a follow-up-visit (hereafter indicated as t1). An additional questionnaire concerning Protection Motivation was given to 215 of these DUs. Twenty five DUs did not receive the questionnaire due to understaffing on the day of their visit; for 5 DUs the reason was unknown. Among the 215 DUs a sample of 92 was selected who met four criteria: a) HIV-negative at t1 (n=210), b) having injected in the four weeks previous to t1 (n=103), c) having a previous visit of less than 9 months ago (n=97) and d) having completed the questionnaire (n=92). The sample consists of 55 males (60%) and 37 females (40%) with a mean age of 32.7 years. A total of 61 (66%) have Dutch nationality, 19 (21%) have German nationality and the other 12 (13%) have various nationalities. The median number of visits in the cohortstudy before t1 is 4 (range 1-14).

The first follow-up visit of these 92 DUs after t1, within a period of 9 months, will be indicated as t2.

Measures

Safe injecting was assessed as follows: a) Did you use a needle and syringe which has been used by somebody else since your last visit, and if so, when was the last time? and b) If so, have you cleaned this needle and syringe, and in which way? For the present analysis, answers which indicated rinsing with bleach and/or boiling were considered is disinfecting. Safe injecting was scored in three categories: 1) borrowed but did not disinfect, 2) borrowed and disinfected and 3) did not borrow. Previous safe injecting refers to safe injecting as reported at t1. At each visit, subjects were asked how they obtained new needles and syringes since their last visit, and to indicate the percentages (adding up to 100%) for four categories: buying, exchanging (at the exchange program), receiving (e.g., from friends) or otherwise. The percentage reported for exchanging was used as measure for the degree of participation in the exchange program. Protection Motivation variables were measured (at t1) as follows.

- Perceived severity of HIV infection: 2 items: (1) seriousness of infection with AIDS-virus; (2) infectiousness of AIDS-virus. Scores ranged from 1 (not at all) to 5 (extremely). Perceived severity was computed by summing these 2 items, with score range from 2 (not at all severe) to 10 (extremely severe). Although Cronbach's alpha was only 0.49, the scale was used as planned.

- Perceived vulnerability to HIV infection by injecting: 2 items: How do you estimate the chance to get infected with the AIDS-virus through injecting: (1) for yourself, (2) for other addicts. Scores ranged from 1 (zero) to 5 (extremely high). Protection Motivation theory concerns only one's own risk (item 1). A comparative risk-score was derived by subtracting the own risk-score from the risk attributed to others (item 2). Scores ranged from 4 (extreme optimism) to -2 (pessimism).

Subjects scoring higher than zero (i.e., who judge their own risk as lower than the risk of others) are indicated as "optimists". -Anxiety. 3 items: How anxious/worried/nervous do you feel when you think about AIDS? Scores ranged from 1 (not at all) to 5 (very). Anxiety was computed by summing these 3 items, with a score range from 3 (not anxious) to 15 (extremely anxious). Cronbach's alpha is 0.87.

- Response efficacy. If someone always uses only his own needles, how certain are you then that that person prevents infection with the AIDS-virus through injecting? The score ranged from 1 (not at all certain) to 5 (extremely certain).

-Self-efficacy: 5 items: (1): How easy or difficult would you find it in the next half year only to inject with your own needles or with safely cleaned needles? The score ranged from 1 (very easy) to 5 (very difficult). The next 4 items represented specific difficult situations (for example, if one is ill with withdrawal symptoms), and were scored the same way. If the answer to the first question was 5 (very difficult), the following 4 times automatically also were scored 5. Self-efficacy was computed by summing the inverted item-scores and ranged from 5 (no self efficacy) to 25 (very good self-efficacy). Cronbach's alpha is 0.84 (corrected alpha 0.82, that is minus the cases with score 5 on item 1, n=91).

- Behavioral intention: Subjects could indicate whether they intended to stop injecting in the next half year. Among those who did not intend to stop injecting, the intention to inject safely was measured with the following item: In emergency situations (i.e., dope available, but no new or self used needle and syringe), how strong is your intention to first boil or clean with bleach somebody else's used needle in the next half year? Possible answers were: 0 (do not know/not at all strong), 1 (not so strong), 2 (strong), 3 (very strong) and 4 (does not intend to borrow at all).

For descriptive purposes, perceived severity, anxiety and self-efficacy were converted to 5 point scales.

RESULTS

Sample characteristics

On average, the 92 current IDUs started injecting 12.1 years before intake in the cohort-study (median 11.5, range 1-28 years). At t1, 75 subjects (82%) reported a history of borrowing. With regard to current daily injecting, 17 subjects (18%) injected heroin, 6 (7%) cocaine and 20 (22%) heroin and cocaine together ("speedball"). Weekly (but not daily) injecting of heroin, cocaine and speedballs was reported by 11 (12%), 11 (12%) and 25 (27%) subjects, respectively. The mean number of injections on injecting days in the previous month was 3.1 (median 2, range 1-14). A new needle and syringe was used a mean number of, 1.7 times (median 1, range 1-9).

Previous safe injecting, degree of participation in the exchange program and protection motivation at t1

With regard to previous safe injecting, 13 IDUs (15%) report borrowing but not disinfecting, 2 (2%) report borrowing and disinfecting and 74 (83%) report not to have borrowed (3 missing). Obtaining all new needles and syringes at the exchange program is reported by 67 IDUs (73%), while 8 (9%) report percentages from 50% to 99%. Seventeen subjects (19%) report not to have used the exchange program since their previous visit: 14 had bought all new needles and syringes, while 3 received new equipment from others.



Table 1 shows the frequency distributions of protection motivation factors. HIV infection is perceived as severe by 91 % (score >4). Forty one percent perceive themselves to be vulnerable to HIV infection through injecting (score >2), while 98% perceive other addicts to be vulnerable to HIV infection. The mean comparative risk-score is 1.9 (s.d. 1.5); 83% of the subjects classify as optimists. Anxiety (score >4) was reported by 28% of the respondents. Response efficacy of using only one's own injection equipment is seen as high (score >4) by 92%, and 61% have a high self-efficacy score (score >4).

With regard to behavioral intentions, 15 IDUs (16%) express the intention to stop injecting. This intention is reported more often by subjects who do not participate in the exchange program. Among 17 non-participants; 6 (35%) report the intention to stop injecting, as compared to 9 (12%) among 75 participants (Fisher's exact test, p=.03). The intention to stop injecting is related neither to previous safe injecting nor to protection motivation variables.

Among the 77 subjects who did not intend to stop injecting, 4 (5%) report a weak or no intention to disinfect when borrowing, 15 (19%) report a strong to very strong intention to disinfect when borrowing and 57 (74%) report that they do not intend to borrow at all (1 missing).

Since scores on most variables were not normally distributed, Spearman's rank order correlation coefficients were used to examine significant bivariate correlations between variables measured at t1. Figure 2 shows that previous safe injecting is positively related to self-efficacy and negatively to perceived vulnerability. This indicates that safe injectors perceive themselves to be at low risk and as able to inject safely, while unsafe injectors feel vulnerable and less able to inject safely. Noteworthy is the relatively strong negative relation between perceived vulnerability and self-efficacy. Perceived vulnerability is negatively related with the intention to inject safely, while perceived severity, response efficacy and self-efficacy are all positively related to this intention.

Since the assumptions necessary for multiple regression analysis or linear discriminant analysis were not met, we employed logistic regression (Hosmer & Lemeshow 1989) to identify independent predictors of intention (dichotomized in 0 (does not exclude borrowing) versus 1 (intention not to borrow at all)). With this technique, the amount of change in the dependent variable for a oneunit change in the independent variable is indicated by the odds ratio (OR), while the partial correlation between the dependent variable and each of the independent variables is indicated by the R statistic, which can range in value from -1 to +1. The goodness-of-fit statistic compares the observed probabilities to those predicted by the model. A significance level greater than .05 indicates that the model does not differ significantly from a "perfect" model. For all analyses, a significance level of .05 was used. In a multivariate logistic regression model with severity, vulnerability, response efficacy and self-efficacy as independent variables, only self-efficacy was an independent and significant predictor of the intention to inject safely (see table 2). No significant interaction was found between vulnerability and self-efficacy in predicting intention.



Own risk, others' risk and unrealistic optimism at t1

Perceived vulnerability of oneself (own risk) is not associated with the perceived vulnerability of other addicts (r---.06, p=.29). The comparative risk score (others' risk-score minus own risk-score) was about equally influenced by both variables: Spearman's correlation between optimism and own risk is -.65, and between optimism and others' risk .76. First, we investigated possible differences in risk judgments as a function of previous safe injecting. Previous safe injecting was negatively related to own risk (see figure 2), not related to others' risk (r=.02, p=.43) and positively related to optimism (r=.22, p=.02). Thus, safe injectors have a low perceived own risk and are more often optimistic about their relative risk. Optimism was positively related to perceived severity (r=.21, p=.02) and to self-efficacy (r=.27, p=.006). Optimism was not related to anxiety, nor to any other Protection Motivation variable.



Indicators of safe injecting at t2

The second measurement (t2, mean time between visits 4.5 months) included 87 subjects, of whom 82 had injected since t1. There was no relation between the intention to stop injecting, as expressed at t1, and injecting at t2. At t2, two HIV seroconversions were observed, both were current injectors at t2. All remaining analyses concern the 82 current injectors at t2, except for relations with the intention to inject safely, which concerns only 70 subjects who did not - at tl - intend to stop injecting. With regard to safe injecting at t2, 5 subjects (6%) report borrowing but not disinfecting, 4 (5%) report borrowing and disinfecting and 73 (89%) report not to have borrowed since t1. Obtaining all new needles and syringes at the exchange program was reported by 58 subjects (71%). Eleven (13%) reported percentages from 1 % to 95%, and 13 (16%) reported not to have used the exchange program since tl.



Two variables of Protection Motivation theory, perceived vulnerability and self-efficacy, predicted safe injecting at t2, while the intention to inject safely (n=70), perceived severity and response efficacy did not. Other indicators of safe injecting at t2 were safe injecting at 0, optimism, and participation in the exchange program at t2. All variables had a positive relation with safe injecting at t2, except perceived vulnerability, which had a negative relation (see figure 3).

Logistic regression analyses showed that the strongest indicators of safe injecting at t2 (dichotomized in 0 (borrowed since t1) versus 1 (did not borrow since t1)) were the degree of participation in the exchange program and vulnerability. With both variables in the model (hereafter indicated as model A; goodness-of-fit statistic p=.76), the odds ratios were 1.02 (per percentage, 95% confidence interval (CI)=1.00-1.04, R=.22) and 0.47 (C1=0.25-0.90, R=-.24), respectively. No other variable contributed significantly to the prediction of safe injecting. A model with only intention and self-efficacy had no predictive power; the same was true for a model with intention, self-efficacy and previous behavior. There were no indications for interaction between intention and self-efficacy. Adjusting model A for previous safe injecting resulted in a weaker relation between vulnerability and safe injecting (adjusted OR=0.54, C/=0.25-1.16, R=-.11). This suggests that the link between vulnerability and safe injecting at follow-up is partly explained by the relation between vulnerability and previous behavior. In order to examine the possibility of interaction between vulnerability and selfefficacy, we entered both self-efficacy and the interaction term for self-efficacy and vulnerability in model A. The interaction term approached significance, but as a whole the model became unstable, due to small numbers, and was not significantly better than model A (improvement x z test p=.13).

Figure 3 summarizes the major effects found in the present study. Optimism (with a bivariate positive correlation with safe injecting at t2 (r-0.24, p=.02)) is not shown. Previous safe injecting is associated with high self-efficacy and low perceived vulnerability. High self-efficacy leads, as expected, to safe injecting at follow-up, but high perceived vulnerability is associated with unsafe injecting at follow-up. Intention is not significantly related to behavior at t2.



Figure 4 shows that most safe injecting (both at t1 and t2) occurs among low vulnerability high self-efficacy subjects (group 2); most unsafe injecting occurs among high vulnerability-low self-efficacy subjects (group 3).

DISCUSSION

The results of the present study do provide support for Protection Motivation theory and improve our understanding of needle sharing by IDUs. As predicted, perceived severity, response efficacy and self-efficacy are positively related to behavioral intention, with self-efficacy being the strongest predictor. Anxiety is related to vulnerability and does not have a direct relation with intention or behavior at follow-up. Self-efficacy is related to intention and to behavior at follow-up. This confirms earlier findings (e.g. Beck & Lund 1981), and is in accordance with the theory of planned behavior (Ajzen 1991). Contrary to expectations, intention does not predict behavior. Ajzen (1991) pointed out that a behavioral intention can only find full expression in behavior under volitional control. Most behaviors, however, depend to some degree on the presence of means and skills. Thus, next to intention, response costs (or actual behavioral control) and self-efficacy (perceived behavioral control) are important. In the present study, degree of participation in the exchange program and perceived vulnerability are associated with safe injecting at follow-up. In an earlier study, degree of participation in the exchange program was also related to safe injecting (Hangers et al. 1991). These findings suggest that participation in the exchange program indeed lowers response costs and improves actual behavioral control. Huang et al. (1989), in a cross-sectional study among IDUs, found that situational factors like response costs were better predictors of safe injecting than health beliefs. However, in the present study, a significant relation between safe behavior and participation in the exchange program was found at follow-up, but not at the first visit. Other studies concerning the Amsterdam exchange program failed to find significant effects of participation on injecting risk behavior (Hangers et al, in press) and on seroconversion rate (Van Ameijden et al, in press). However, those studies compared regular and full time attenders with irregular and non-attenders, while in the present and earlier study a continuous variable is employed. These findings suggest that the relation between participation in the exchange program and safe injecting is weak. This may be due to the fact that attenders have different characteristics than nonattenders (Hangers et al., in press). Further investigations seem necessary.

Similar to findings by Joseph et al. (1987), the relation between perceived vulnerability and safe behavior at follow-up is negative. This negative effect of perceived vulnerability on behavior is independent of self-efficacy and of degree of participation in the exchange program. Although no interaction is found, the results nevertheless suggest the presence of feelings of hopelessness or fatalism. High perceived vulnerability is associated with previous unsafe injecting, while this perceived vulnerability does not stimulate subjects to change their behavior: they do not intend to inject safely and continue to inject unsafely at follow-up. Most unsafe injecting occurs among subjects with high perceived vulnerability and low self-efficacy. In an earlier cross-sectional study, Magura et al. (1989) also found an indication that needle sharing is related to fatalism about developing AIDS. However, Magura's study concerned IDUs of unknown serostatus and needle sharing included both giving away used equipment and using others' equipment. Conversely, our results also point to the existence of a group of injectors with low perceived vulnerability and high self-efficacy, who inject safely at both measurements. This seems to concern IDUs who correctly assess their (relatively low) risk.

Perceived vulnerability and optimism

The degree of optimism is high as compared to other studies among high risk groups (Bauman & Siegel 1987, Joseph et al. 1987, Van der Velde, van der Pligt & Hooykaas, in press). Since optimism in these studies concerns risk through sexual behavior, they may not be comparable. Correlations between risk judgements and self-reported behaviors are seldom significant (Weinstein 1984, 1989). However, in the present sample perceived vulnerability is related both to self-efficacy and previous safe behavior, which indicates that perceived risk is a function of previous behavior. This is similar to findings by Van der Velde, van der Pligt & Hooykaas (in press). As a result of the negative relation between own risk and safe injecting at follow-up, we found optimism - contrary to the expectations - positively associated with safe injecting at follow-up. Thus, our findings do not show adverse behavioral consequences of optimism. Optimism is positively related to self-efficacy (or perceived behavioral control), which points to a cognitive origin of optimism. Mixed support was found for the motivational explanation of optimism: in the present study, optimism is indeed positively related to the perceived severity of the threat. However, (different from findings by Bauman & Siegel (1987) among homosexual men), anxiety is not related to optimism, which pleads against defensive coping as an underlying mechanism.

IDUs in the present sample seem to estimate their own risk as a function of their previous behavior, but have extremely high risk estimates for other addicts. Thus, optimism seems the result of overestimating others' risk rather than of underestimating one's own risk (similar to Perloff & Fetzer (1986) and Van der Velde, van der Pligt & Hooykaas (in press)). In fact, the high risk estimates for others do not seem very unrealistic: all IDUs in the current sample are HIV-negative, despite their previous risk behavior, while the prevalence among Amsterdam injectors is estimated at approximately 30% (Van Haastrecht et al. 1991).

Previous behavior

In line with other findings (see introduction), previous behavior is predictive of behavior at follow-up, which may indicate habit. Furthermore, previous behavior appears to influence perceived vulnerability, and the effect which perceived vulnerability has on behavior at follow-up is partly attributable to previous behavior. However, previous behavior does not have an independent effect on later behavior, next to vulnerability and participation in the exchange program. This suggests that, in the present sample, cognitive factors and actual behavioral control are more important in determining behavior than previous behavior.

Conclusions and implications for prevention

Two important corollaries can be made. First, the present study shows that HIV-negative subjects, aware of their serostatus, differ widely in health beliefs, partly as a function of their previous risk behavior. In turn, these health beliefs are partly related to subsequent risk behavior. These findings suggest that studies of the effect of counseling and testing on HIV risk behavior (see for an overview Higgins et al. 1991) need to take cognitive factors into account. Second, among subjects aware of a seropositive serostatus, the wish for protection of others against HIV can be assumed to be an important determinant of behavior. Among subjects unaware of their serostatus, assumptions concerning one's serostatus may influence health beliefs and behavior. Consequently, it seems highly important to consider serostatus and knowledge of serostatus in studies of the relations between cognitive factors and behavior.

The implications for prevention can be summarized as follows. Protection motivation is based on threat appraisal and coping appraisal. The present findings suggest that, for many IDUs, actual and perceived

behavioral control (or coping appraisal) is relatively low. A number of subjects feel unable to cope and see themselves as extremely vulnerable to HIV infection. This leads - possibly through feelings of hopelessness and/or fatalism - to unsafe injecting. As argued before, a heightened awareness of being at risk can result in maladaptive behavior; this implies that too much emphasis on the high vulnerability of IDUs may be undesirable. Measures like skills training and improved accessibility of new needles and syringes or disinfectants may be effective in increasing actual and perceived behavioral control (see also Paulussen et al. 1990 and Kok & Sandfort 1991). A better balance between threat and coping appraisal may result in more safe behavior.

ACKNOWLEDGMENTS

This study was supported by the Netherlands Foundation for Preventive Medicine (grant no. 28-1258). The authors thank the nurses B. Fr6lich, B. Scheeringa-Troost and R. Lopes Diaz for interviewing and collecting blood samples; Dr. J. Goudsmit and M. Bakker for performing the laboratory tests; H.J.A. van Haastrecht for data management; J.A.R. van den Hoek and R.A. Coutinho for providing the opportunity to conduct this research and M. ter Pelle for preparing the manuscript.

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