The lack of selection bias in a snowball sampled case-control study on drug abuse

Snowball Sampling Study Design for Serosurveys Early in Disease Outbreaks

Serological surveys can provide evidence of cases that were not previously detected, depict the spectrum of disease severity, and estimate the proportion of asymptomatic infections. To capture these parameters, survey sample sizes may need to be very large, especially when the overall infection rate is still low. Therefore, we propose the use of "snowball sampling" to enrich serological surveys by testing contacts of infected persons identified in the early stages of an outbreak. For future emerging pandemics, this observational study sampling design can answer many key questions, such as estimation of the asymptomatic proportion of all infected cases, the probability of a given clinical presentation for a seropositive individual, or the association between characteristics of either the host or the infection and seropositivity among contacts of index individuals. We provide examples, in the context of the coronavirus disease 2019 (COVID-19) pandemic, of studies and analysis methods that use a snowball sample and perform a simulation study that demonstrates scenarios where snowball sampling can answer these questions more efficiently than other sampling schemes. We hope such study designs can be applied to provide valuable information to slow the present pandemic as it enters its next stage and in early stages of future pandemics.

Patagonian grouper Acanthistius patachonicus (Jenyns, 1840) forms massive spawning aggregations in the Southwest Atlantic

Here we describe massive spawning aggregations and seasonal changes in the large-scale distribution of the Patagonian grouper Acanthistius patachonicus in the Southwest Atlantic based on three sources of information: (a) data from bottom trawl research surveys covering the distributional range of the species within the Argentine continental shelf; (b) folk ecological knowledge gathered from experienced captains of the Argentine industrial trawl fisheries; and (c) sampling of an artisanal trap fishery targeting the Patagonian grouper in a specific location off the coast of Buenos Aires Province. The trawl surveys showed a general pattern of aggregation of Patagonian grouper towards the coast during the reproductive period (September-December). Captains described massive aggregations of the species at specific near-shore locations, where trawl catches of up to 15 t in a single haul were registered during the reproductive season. At a local scale, the artisanal trap fishery described operates exclusively during the reproductive period, targeting near-shore aggregations with a high proportion of individuals releasing gametes onboard. These three sources of information provide evidence of the existence of massive transient spawning aggregations of Patagonian grouper in the Argentine shelf. This is the first report of a reef fish spawning aggregation in the southern region of the Southwest Atlantic. Anecdotal information gathered in this study points to the depletion of many of the aggregations targeted during the 1980s and 1990s by the industrial fleet. At the same time, the spawning aggregation site off Buenos Aires Province has been productive for the last 34 years, being exploited exclusively by traps. The Patagonian grouper is classified as Data Deficient by the International Union for Conservation of Nature, which highlights the need for further research to determine its stock status. Mapping its current spawning aggregations should be a priority to inform the design of a targeted monitoring program and management plan for this species.

Potential risk factors for celiac disease in childhood: a case-control epidemiological survey

Background: Celiac disease (CD) prevalence has increased significantly in recent decades in some developed countries. Yet the environmental factors in the existing literature do not appear to provide a satisfactory explanation for this increase.

Objective: To determine whether nine variables are associated with CD in children. These variables are: incidence of ear infection before 2 years old, courses of antibiotics before 2 years old, duration of breastfeeding, vitamin D drop exposure in infancy, vitamin D supplement exposure between 2–3 years old, age at gluten introduction into the diet, fat content of cow’s milk consumed between 2–3 years old, quantity of cow’s milk consumed between 2–3 years old, and type of water consumed at 2 years old.

Methods: An Internet-based survey was conducted among parents living in the US with at least one biological child between 3 and 12 years old. Potential participants were informed about the survey through social media, websites, electronic newsletters, and advertisements.

Results: After exclusions, there remained 332 responses associated with children with CD (cases), and 241 responses associated with children who do not have CD (controls). In this data set, skim milk as the primary form of liquid cow’s milk consumed between 2–3 years old (adjusted odds ratio [aOR]=3.556, CI=1.430–10.22, P=0.010), vitamin D drops administered for more than 3 months (aOR=1.749, CI=1.079–2.872, P=0.025), courses of antibiotics (aOR=1.133, CI=1.037–1.244, P=0.007), and incidence of ear infection (aOR=1.183, CI=1.041–1.348, P=0.010) are all associated with CD in children.

Conclusions: This study is the first to find an association between skim milk consumption and CD and vitamin D drop use for greater than 3 months and CD. It also adds to evidence that early life exposure to antibiotics and early life infection, specifically ear infection, are associated with CD.

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Acetaminophen, antibiotics, ear infection, breastfeeding, vitamin D drops, and autism: an epidemiological study

BACKGROUND

While many studies have examined environmental risk factors for autism spectrum disorder (ASD), much of the research focus has been on prenatal or perinatal factors. Yet, the postnatal environment may affect the risk of ASD as well.

OBJECTIVE

To determine whether a set of five postnatal variables are associated with ASD. These variables are: acetaminophen exposure, antibiotic exposure, incidence of ear infection, decreased duration of breastfeeding, and decreased consumption of oral vitamin D drops.

MATERIALS AND METHODS

An Internet-based survey was conducted. Participants were parents living in the USA with at least one biological child between 3 and 12 years of age. Potential participants were informed about the survey via postings on social media, websites, and listservs and were offered an opportunity to participate in a raffle as well. Participants were also recruited through the Interactive Autism Network.

RESULTS

There were 1,741 completed survey responses. After exclusions, there remained 1,001 responses associated with children with ASD (cases) and 514 responses associated with children who do not have ASD (controls). In this data set, doses of postnatal acetaminophen (adjusted odds ratio [aOR] 1.016, CI: 1.003-1.032, p=0.026), courses of postnatal antibiotics (aOR 1.103, CI: 1.046-1.168, p<0.001), incidence of postnatal ear infection (aOR 1.137, CI: 1.046-1.236, p=0.003), and decreased duration of breastfeeding (aOR 0.948, CI: 0.932-0.965, p<0.001) are all associated with ASD when adjusted for eight demographic variables. A weak association between oral vitamin D drop exposure and ASD was also found when adjusted for breastfeeding and demographics (aOR 1.025, CI: 0.995-1.056, p=0.102).

CONCLUSION

This study adds to evidence that postnatal acetaminophen use, postnatal antibiotic use, incidence of ear infection, and early weaning are associated with an increased risk of ASD. It also finds that postnatal oral vitamin D drops are weakly associated with ASD when adjusted for breastfeeding and demographics.

Influence of depressive symptoms on distress related to positive psychotic-like experiences in women

The Community Assessment of Psychic Experiences (CAPE) is an effective instrument for detection of the presence of psychotic symptoms and associated distress in the general population. However, little research has studied distress associated with positive psychotic-like experiences (PLEs). Our aim is to study PLE-related distress using the CAPE. In this study we analysed factors associated with differences in PLE-related distress in a sample of 200 non-clinical participants recruited by snowball sampling. Presence of PLEs and related psychological distress was measured using the CAPE questionnaire. The influence of age, gender, educational level and drug use was studied. In univariate analysis we found that gender and CAPE positive, depressive and negative scores, were associated with CAPE positive distress. Using multiple linear regression, we found that only the effect of gender, and the interaction between frequency of depression and gender, remained statistically significant. In our sample interaction between gender and depressive symptoms is a determining factor in distress associated with positive PLEs. The results of this study may be useful for the implementation of prevention programs.

U-shaped curve of psychosis according to cannabis use: New evidence from a snowball sample

BACKGROUND

The aim of this study was to investigate the relationship between psychotic-like experiences (PLEs) assessed using the Community Assessment of Psychic Experience (CAPE) questionnaire and the pattern of cannabis use in a non-clinical sample collected by snowball sampling.

METHODS

Our sample was composed of 204 subjects, distributed into three groups by their cannabis use pattern: 68 were non-cannabis users, 40 were moderate cannabis users and 96 were daily cannabis users. We assessed the psychotic experiences in each group with the CAPE questionnaire; and then controlled for the effect of possible confounding factors like sex, age, social exclusion, age of onset of cannabis use, alcohol use and other drug use.

RESULTS

We found a significant quadratic association between the frequency of cannabis use and positive (β = -1.8; p = 0.004) and negative dimension scores (β = -1.2; p = 0.04). The first-rank and mania factors showed a significant quadratic association (p < 0.05), while the voices factor showed a trend (p = 0.07). Scores for the different groups tended to maintain a U-shape in their values for the different factors. When we adjusted for gender, age, social exclusion, age of onset of cannabis use, and use of alcohol and other drugs, only the first-rank experiences remained significant.

CONCLUSIONS

We found there was a U-shaped curve in the association between cannabis use and the positive and negative dimensions of the CAPE score. We also found this association in mania and first-rank experiences.

Depletion of trophy large-sized sharks populations of the Argentinean coast, south-western Atlantic: insights from fishers' knowledge

Abstract Globally, sharks are impacted by a wide range of human activities, resulting in many populations being depleted. Trophy large-sized sharks of the Argentinean coast, the sand-tiger Carcharias taurus , the copper Carcharhinus brachyurus and the sevengill shark Notorynchus cepedianus are under intense sport and artisanal fishing since the 50's decade. However, the current and historical information for the assessment of its populations status is scarce. The aim of this work was to analyze the status of conservation of these species through the gathering of expert fishermen knowledge (FK) on semi-structured interviews. Abundance variation perception between the beginning and the end of fishermen careers revealed a critical status for the species study (means variation between -77 and -90 %). Furthermore, a best day's catch analysis reinforce this result in the case of the sand tiger shark. The school shark Galeorhinus galeus was included on this work with the objective of contrast FK with formal information available of catch-per-unit-effort (CPUE) time series. Both sources of information, despite are not comparable, shows declines ~ - 80%. The critical conservation situation of study species needs urgent management action, particularly for the san tiger shark which could became regionally extinct before the reaction of stakeholders occurs.

Non-work at work: Resistance or what?

Based on 43 interviews conducted with employees who spend around half of their working-hours on non-work related activities such as ‘cyberloafing’, a typology of empty labour is suggested according to sense of work obligation and potential output in order to set the phenomenon of workplace time-appropriation into a theoretical context in which wasteful aspects of organization and management are taken into account. Soldiering, which emanates from a weak sense of work obligation in the individual, may entail aspects of resistance, but there are also less voluntary forms of empty labour deriving from a lack of relevant work tasks. All types of empty labour are, however, bound up with the simulation of productivity. Therefore, they ironically serve to maintain the capitalist firm’s reputation for efficiency.

Dose-response effect between cannabis use and psychosis liability in a non-clinical population: evidence from a snowball sample

This study aimed to explore the associations between daily cannabis use and the specific profiles of subclinical symptoms in a non-clinical population obtained through snowball sampling, taking into account alcohol use, other drug use, social exclusion and age at onset of cannabis use. We included 85 daily cannabis users and 100 non-daily cannabis users. Both the case and the control populations were identified by snowball sampling. Daily cannabis use was associated with more alcohol intake and other drug use, as well as with early onset in the use of cannabis. Daily cannabis use appeared to exert a dose-response effect on first-rank symptoms, mania symptoms and auditory hallucinations, even after adjusting for sex, age, other drug use, social exclusion and age at onset of cannabis use. The paranoid dimension was only associated with the heaviest consumption of cannabis. Initial age of cannabis use modified the effects of daily cannabis use on the first-rank and voices experiences. Daily cannabis use was associated with significantly more first-rank and voices experiences among those subjects who started to use cannabis before 17 years of age. Our study supports the association of psychotic experiences with cannabis use even among non-psychotic subjects.

Mitragyna speciosa use in the northern states of Malaysia: a cross-sectional study

ETHNOPHARMACOLOGICAL RELEVANCE

The consumption of Mitragyna speciosa (MS) for its psychoactive effects is widely reported amongst people in the villages in Thailand and Malaysia even though its use is illegal.

AIM OF THE STUDY

This study examined the pattern of MS use, its reported effects and explored its potential to cause dependence.

MATERIALS AND METHODS

We used both convenience and snowball-sampling methods to recruit participants in a border town between two northern states in Malaysia. Face-to-face interviews were conducted with the use of a structured questionnaire on 562 respondents who gave oral consent to participate in the study.

RESULTS

The response rate was 91%. The majority of the respondents (88%) reported daily use of MS. The main mode of using MS was by drinking the MS extract as tea (90%). The mean age of starting MS use was 28.3 (SD=8.1) years. A variety of reasons were given for using MS including for social and recreational needs, stamina and physical endurance, pain relief and improved sexual performance. Despite its reported usefulness in weaning off opiate addiction, 460 (87%) admitted they were not able to stop using MS. Only education level had a statistically significant association with the ability to stop or not stop the use of MS (χ(2)=31.0, df=1, p<0.001). Significantly higher proportions of those with a lower education level (38%) were able to stop using MS compared to respondents with a higher education level.

CONCLUSIONS

Our study provides important information on the pattern of MS use, its effects and its potential to cause addiction, as there has been growing interest in MS as evidenced by the number of advertisements for its sale on the Internet. Future study is required to explore its psychological and social impact on users.

Evaluation of quality of life in adults with chronic health conditions: the role of depressive symptoms

OBJECTIVE: The negative impact of depressive symptoms on quality of life has been the focus of increasing attention, yet this relation remains unstudied in samples from developing countries. The objective of this study was to determine whether the occurrence of depressive symptoms is associated with impaired quality of life and whether this association remains significant after adjustment for some variables. METHOD: A convenience sample was selected and the measures used were the WHOQOL-100, to assess quality of life, the Beck Depression Inventory, to screen for depressive symptoms, and the Economic Classification Criterion - Brazil, to evaluate socioeconomic status. RESULTS: One hundred nineteen healthy adults (community) and 122 adult patients (tertiary hospital) from Brazil were assessed. Depressive symptoms were negatively correlated with all the domains of quality of life, even after statistical control for age, socioeconomic status, and presence of chronic health conditions. Socioeconomic status was positively correlated with the social relationships and environmental domains of quality of life. CONCLUSION: Our findings indicate that depressive symptoms and socioeconomic status are important elements affecting the relationship between chronic health conditions and quality of life in Brazil.

Longitudinal community plasma HIV-1 RNA concentrations and incidence of HIV-1 among injecting drug users: prospective cohort study

OBJECTIVE

To examine the relation between plasma HIV-1 RNA concentrations in the community and HIV incidence among injecting drug users.

DESIGN

Prospective cohort study.

SETTING

Inner city community in Vancouver, Canada.

PARTICIPANTS

Injecting drug users, with and without HIV, followed up every six months between 1 May 1996 and 30 June 2007.

MAIN OUTCOME MEASURES

Estimated community plasma HIV-1 RNA in the six months before each HIV negative participant's follow-up visit. Associated HIV incidence.

RESULTS

Among 622 injecting drug users with HIV, 12 435 measurements of plasma HIV-1 RNA were obtained. Among 1429 injecting drug users without HIV, there were 155 HIV seroconversions, resulting in an incidence density of 2.49 (95% confidence interval 2.09 to 2.88) per 100 person years. In a Cox model that adjusted for unsafe sexual behaviours and sharing used syringes, the estimated community plasma HIV-1 RNA concentration remained independently associated with the time to HIV seroconversion (hazard ratio 3.32 (1.82 to 6.08, P<0.001), per log(10) increase). When the follow-up period was limited to observations after 1 January 1988 (when the median plasma HIV RNA concentration was <20 000 copies/ml), the median viral load was no longer statistically associated with HIV incidence (1.70 (0.79 to 3.67, P=0.175), per log(10) increase).

CONCLUSIONS

A longitudinal measure of community plasma HIV-1 RNA concentration was correlated with the community HIV incidence rate and predicted HIV incidence independent of unsafe sexual behaviours and sharing used syringes. If these findings are confirmed, they could help to inform both HIV prevention and treatment interventions.

Regional differences in HIV prevalence among drug users in China: potential for future spread of HIV?

Background

Drug use and in particular injecting drug use has been at the forefront of the explosive spread of HIV in general populations in many countries in Asia. There is concern that also in China increased HIV incidence in drug users might spark off a generalized epidemic in the wider population. Close monitoring of HIV incidence and risk factors in drug users is therefore important to be able to target interventions effectively. Second generation surveillance was launched to assess HIV prevalence and risk behaviours jointly with the purpose of describing trends and predicting future developments. To assess whether these goals were fulfilled among drug users in China we provide an analysis of risk factors for HIV infection and of regional differences in HIV prevalence.

Methods

We analysed data collected in 2005 in 21 drug user second generation surveillance sentinel sites from 14 provinces in China. We used random effects logistic regression to test for risk factors for HIV infection and regional differences.

Results

The overall HIV-1 antibody prevalence was 5.4% (279/5128); 4.9% among injecting drug users (IDU) not sharing needles and 3.7% among non-injecting drug users. We found substantial heterogeneity among the surveillance sites with prevalence rates ranging between 0% and 54%. HIV status was strongly affected by the regional prevalence of HIV. Risk behaviours were highly prevalent in regions where HIV prevalence is still low. The distribution of duration of drug use in different sites indicated different stages of the drug use epidemics.

Conclusion

]Regional differences in HIV prevalence in China reflect different stages of the drug use and HIV epidemics rather than differences in risk behaviours. Therefore, outbreaks of HIV among drug users in regions where prevalence is still low can be expected in the future. However, methodological limitations of surveillance embedded into routine systems limit the usability of existing data. More standardized approaches to data collection in secondary generation HIV surveillance are necessary to better understand regional differences in risk behaviour and prevalence and to design targeted intervention for those regions at risk of experiencing outbreaks.

Health-related quality of life in diabetic patients and controls without diabetes in refugee camps in the Gaza strip: a cross-sectional study

BACKGROUND

Prevalence of diabetes mellitus is increasing in developed and developing countries. Diabetes is known to strongly affect the health-related quality of life (HRQOL). HRQOL is also influenced by living conditions. We analysed the effects of having diabetes on HRQOL under the living conditions in refugee camps in the Gaza strip.

METHODS

We studied a sample of 197 diabetic patients who were recruited from three refugee camps in the Gaza strip and 197 age- and sex-matched controls living in the same camps. To assess HRQOL, we used the World Health Organization Quality of Life questionnaire (WHOQOL-BREF) including four domains (physical health, psychological, social relations and environment). Domain scores were compared for cases (diabetic patients) and controls (persons without diabetes) and the impact of socio-economic factors was evaluated in both groups.

RESULTS

All domains were strongly reduced in diabetic patients as compared to controls, with stronger effects in physical health (36.7 vs. 75.9 points of the 0-100 score) and psychological domains (34.8 vs. 70.0) and weaker effects in social relationships (52.4 vs. 71.4) and environment domains (23.4 vs. 36.2). The impact of diabetes on HRQOL was especially severe among females and older subjects (above 50 years). Low socioeconomic status had a strong negative impact on HRQOL in the younger age group (<50 years).

CONCLUSION

HRQOL is strongly reduced in diabetic patients living in refugee camps in the Gaza strip. Women and older patients are especially affected.

Compared to what? Finding controls for case-control studies

Use of control (comparison) groups is a powerful research tool. In case-control studies, controls estimate the frequency of an exposure in the population under study. Controls can be taken from known or unknown study populations. A known group consists of a defined population observed over a period, such as passengers on a cruise ship. When the study group is known, a sample of the population can be used as controls. If no population roster exists, then techniques such as random-digit dialling can be used. Sometimes, however, the study group is unknown, for example, motor-vehicle crash victims brought to an emergency department, who may come from far away. In this situation, hospital controls, neighbourhood controls, and friend, associate, or relative controls can be used. In general, one well-selected control group is better than two or more. When the number of cases is small, the ratio of controls to cases can be raised to improve the ability to find important differences. Although no ideal control group exists, readers need to think carefully about how representative the controls are. Poor choice of controls can lead to both wrong results and possible medical harm.

A case-control study of the association of diet and obesity with gout in Taiwan

BACKGROUND

Gout has been a significant metabolic disorder for Chinese men in Taiwan; however, there is insufficient information on diet and lifestyle risk factors in this population.

OBJECTIVE

The purpose of this case-control study was to explore potential dietary and lifestyle risk factors associated with gout in Chinese men.

DESIGN

Between 1998 and 1999, we recruited and conducted face-to-face interviews with patients from outpatient clinics in Taipei who had incident gout (n = 92) and with their healthy coworkers (controls; n = 92).

RESULTS

Systolic blood pressure, diastolic blood pressure, waist-to-hip ratio, waist-to-height ratio, and body mass index were significantly higher in cases than in controls. Family histories of gout and diabetes mellitus were strong risk factors for gout. Frequencies of vegetable and fruit consumption were significantly lower in cases than in controls. Logistic regression analyses showed that high alcohol intake and low intakes of fiber, folate, and vitamin C increased the risk of gout, but no association was found with purine intake. After covariates were controlled for, the adjusted odds ratios for the middle and highest tertiles of waist-to-height ratio (0.50-0.54 and >/==" BORDER="0"> 0.55, respectively) were 3.89 (95% CI: 1.32, 11.46) and 4.37 (1.18, 16.22), respectively, but no linear association was found for waist-to-hip ratio and waist circumference.

CONCLUSIONS

Consumption of alcohol, but not of purine, may be a significant dietary risk factor for gout. Food sources rich in dietary fiber, folate, and vitamin C, such as fruit and vegetables, protect against gout. Waist-to-height ratio, which indicates central obesity, has a significant linear effect on gout occurrence, independent of body mass index.

A case-control study on alcohol and psychiatric disorders as risk factors for drug abuse pattern

We evaluated alcohol and psychiatric disorders as risk factors for the pattern of drug abuse/dependence in a matched case-control study (370 adults). Cases (drug abusers) and controls were selected in the community using the snowball technique and matched by sex, age, and friendship. Information was gathered using the "Composite International Diagnostic Interview" (CIDI). Three patterns of drug abuse/dependence were evaluated: any drug abuse/dependence, only cannabis, and cocaine and other drugs. Logistic conditional regression showed that alcohol dependence was strongly associated with pattern of drug abuse/dependence. Thus, compared to the "no drug abuse group", the odds ratio for association with diagnosis of abuse/dependence on cocaine and other drugs was 10.2 (95% CI: 4.9-21.2), whereas for abuse/dependence on cannabis only, the odds ratio was 1.0. For affective disorders, the odds ratio was 2.0 (95% CI: 1.10-3.64) for the group that received a diagnosis of abuse/dependence on cocaine and other drugs, whereas no association was found for those with abuse/dependence on cannabis only. In conclusion, there is not a homogeneous group of "drug users", and the role of risk factors depends on the drug use pattern.

International study of expert judgment on therapeutic use of benzodiazepines and other psychotherapeutic medications: VI. Trends in recommendations for the pharmacotherapy of anxiety disorders, 1992-1997

OBJECTIVE

To assemble expert clinical experience and judgment regarding the treatment of anxiety disorders in a systematic, quantitative manner, particularly with respect to changes during the preceding five years.

METHOD

A panel of 73 internationally recognized experts in the pharmacotherapy of anxiety and depression was constituted by multistage peer nomination. Sixty-six completed a questionnaire in 1992, and 51 of those completed a follow-up questionnaire in 1997. This report focuses on the experts' responses to questions about therapeutic options relevant to seven vignettes describing typical cases of different anxiety disorders.

RESULTS

The preferred initial treatment strategy in 1992 was a combination of medication with a psychological therapy for all vignettes except simple phobia, where a psychological procedure alone was favored. There was little change in 1997, primarily some decrease in the choice of psychological therapy and some increase in the choice of medication for social phobia. Experts recommending a medication in 1992 most often chose as first-line treatment a benzodiazepine anxiolytic (BZ) for panic disorder (PD), generalized anxiety disorder (GAD), simple phobia, and adjustment disorder. They recommended a beta-blocker most often for social phobia and a tricyclic anti-depressant (TCA) for agoraphobia and obsessive-compulsive disorder (OCD). Nearly a fourth chose a combination of medications, usually a TCA plus a BZ. In 1997, the expert panel's most frequent recommendation for agoraphobia, PD, and OCD changed to a specific serotonin reuptake inhibitor (SSRI); and they also recommended these compounds more often for GAD, social phobia, and simple phobia. Fewer experts chose BZs or TCAs. However, in 1997 many again chose a combination of medications, often a BZ plus a SSRI, so that, overall, there was only a small decline in recommendations for BZs. As second-line medications (1997 only), the experts recommended SSRIs most often for most vignettes, but a TCA for PD and GAD. Recommendations for a combination of medications rose substantially for most vignettes, usually a BZ plus an antidepressant.

CONCLUSIONS

Combined cognitive-behavioral therapy plus medication was highly favored by the experts as the initial treatment strategy for anxiety disorders. During the preceding five years, SSRIs displaced older antidepressants as the experts' first-line choices for the pharmacotherapy of anxiety disorders. In case of an unsatisfactory response, the experts' second-line choices more often were an older antidepressant or a combination of an antidepressant plus a BZ. According to the experts' judgements, the BZs, especially combined with an antidepressant, remain mainstays of pharmacotherapy for anxiety disorders.

Snowball sampling by mail: application to a survey of smokers in the general population

BACKGROUND

In a series of surveys intended for current and former smokers but sent to a random sample of the general population, we asked never smokers and smokers who did not wish to participate to transmit the questionnaire to any ever smoker they knew. We compared participants who received the questionnaire directly from us (original participants) to participants who received it from an addressee (secondary participants).

METHODS

Questionnaires on smoking were mailed to 3300 residents of Geneva (Switzerland) in 1997, and returned by 1167 people (35%).

RESULTS

The final sample consisted of similar numbers of original participants (n = 578, primary response rate = 18% of total sample, or about 46% of ever smokers) and secondary participants (n = 566). Original participants were 1.7 years older than secondary participants (P = 0.03) and were more likely to be men (50% versus 43%, P = 0.009). Proportions of current smokers, stages of change, confidence in ability to quit smoking, cigarettes per day and attempts to quit smoking were similar in the two groups. Secondary participants had lower self-efficacy scores (-0.30 standard deviation (SD) units, P < 0.03), and they derived more pleasure from smoking (+0.25 SD units, P = 0.04). Among ex-smokers, direct participants were less active than secondary participants in coping with the temptation to smoke (-0.58 SD units, P = 0.002). Associations between smoking-related variables were similar in original and secondary participants.

CONCLUSION

Allowing non-eligible addressees to transmit the questionnaire to someone else doubled the response rate, produced moderate bias on some variables only and had no detectable impact on associations between smoking-related variables.

[Mental disorders as risk factors for the development of cocaine abuse/dependence: case-control study]

OBJECTIVE

To evaluate the role of psychiatric disorders and alcohol dependence as possible risk factors for cocaine abuse/dependence.

METHODS

The case-control study used the "snowball" technique in order to select untreated cocaine users (cases) and to match sex, age and friendship. Information was gathered using the Composite International Diagnostic Interview (CIDI), and computer diagnosis were generated according to the DSM-III-R criteria. The analysis was performed through the logistic conditional regression.

RESULTS

The study included 208 subjects. The main results showed that having a history of alcohol dependence was independently associated with an increased risk of cocaine abuse/dependence (OR=15,1; 95% CI 3,8-60, 2); no other psychiatric disorder was significantly associated with an increase in this risk after the multivariate analysis. An increased risk of cocaine abuse/dependence was also found for those who related suicide thoughts (OR=3,1; 95% CI 0,91-10,8), suggesting an association between more severe manifestations of depression and cocaine abuse.

CONCLUSIONS

These findings suggest that programs directed towards the treatment and prevention of cocaine abuse must be prepared to address issues related to comorbidity of drug abuse with alcohol and other psychiatric disorders

Prevalence and risk factors for HBV, HCV and HDV infections among injecting drug users from Rio de Janeiro, Brazil

Viral hepatitis constitutes a major health issue, with high prevalence among injecting drug users (IDUs). The present study assessed the prevalence and risk determinants for hepatitis B, C and D viruses (HBV, HCV and HDV) infections among 102 IDUs from Rio de Janeiro, Brazil. Serological markers and HCV-RNA were detected by enzyme immunoassay and nested PCR, respectively. HCV genotyping was determined by restriction fragment length polymorphism analysis (RFLP). HBsAg, anti-HBc and anti-HBs were found in 7.8, 55.8 and 24. 7% of IDUs, respectively. In the final logistic regression, HBV infection was independently associated with male homosexual intercourse within the last 5 years (odds ratio (OR) 3.1; 95% confidence interval (CI) 1.1-8.8). No subject presented anti-delta (anti-HD). Anti-HCV was detected in 69.6% of subjects, and was found to be independently associated with needle sharing in the last 6 months (OR 3.4; 95% CI 1.3-9.2) and with longer duration of iv drug use (OR 3.1; 95% CI 1.1-8.7). These data demonstrate that this population is at high risk for both HBV and HCV infection. Among IDUs from Rio de Janeiro, unprotected sexual intercourse seems to be more closely associated with HBV infection, whereas HCV is positively correlated with high risk injecting behavior. Comprehensive public health interventions targeting this population and their sexual partners must be encouraged.

Epidemiological methods for research with drug misusers: review of methods for studying prevalence and morbidity

Epidemiological studies of drug misusers have until recently relied on two main forms of sampling: probability and convenience. The former has been used when the aim was simply to estimate the prevalence of the condition and the latter when in depth studies of the characteristics, profiles and behaviour of drug users were required, but each method has its limitations. Probability samples become impracticable when the prevalence of the condition is very low, less than 0.5% for example, or when the condition being studied is a clandestine activity such as illicit drug use. When stratified random samples are used, it may be difficult to obtain a truly representative sample, depending on the quality of the information used to develop the stratification strategy. The main limitation of studies using convenience samples is that the results cannot be generalised to the whole population of drug users due to selection bias and a lack of information concerning the sampling frame. New methods have been developed which aim to overcome some of these difficulties, for example, social network analysis, snowball sampling, capture-recapture techniques, privileged access interviewer method and contact tracing. All these methods have been applied to the study of drug misuse. The various methods are described and examples of their use given, drawn from both the Brazilian and international drug misuse literature.

Risk factors for human T cell lymphotropic virus type I among injecting drug users in northeast Brazil: possibly greater efficiency of male to female transmission

It was observed in the city of Salvador, State of Bahia, the highest seroprevalence of human T cell lymphotropic virus type 1 (HTLV-I) infection in Brazil as demonstrated by national wide blood bank surveys. In this paper, we report results of an investigation of drug use and sexual behavior associated with HTLV-I infection among male and female injecting drug users (IDUs) in Salvador. A cross sectional study was conducted in the Historical District of Salvador from 1994-1996 (Projeto Brasil-Salvador) and 216 asymptomatic IDUs were selected using the snowball contact technique. Blood samples were collected for serological assays. Sera were screened for human immunodeficiency virus (HIV-1/2) and HTLV-I/II antibodies by ELISA and confirmed by Western blot. The overall prevalence of HTLV-I/II was 35.2% (76/216). The seroprevalence of HTLV-I, HTLV-II and HIV-I was for males 22%, 11.3% and 44.1% and for females 46.2%, 10.3% and 74.4% respectively. HTLV-I was identified in 72.4% of HTLV positive IDUs. Variables which were significantly associated with HTLV-I infection among males included needle sharing practices, duration of injecting drug use, HIV-I seropositivity and syphilis. Among women, duration of injecting drug use and syphilis were strongly associated with HTLV-I infection. Multivariate analysis did not change the direction of these associations. Sexual intercourse might play a more important role in HTLV-I infection among women than in men.

International Study of Expert Judgement on Therapeutic Use of Benzodiazepines and Other Psychotherapeutic Medications: V. Treatment strategies in panic disorder, 1992-1997

The objective of this study was to assemble expert clinical experience and judgment regarding the treatment of panic disorder in a systematic, quantitative manner, particularly with respect to changes during the past 5 years. A panel of 73 internationally recognized experts in the field of pharmacotherapy of anxiety and depression was constituted by multistage peer nomination. Sixty-six experts completed a questionnaire in 1992, and 51 of those completed a follow-up questionnaire in 1997. This report focuses on the experts' responses to questions about therapeutic options as they relate to a vignette describing a typical case of panic disorder. The preferred initial treatment strategy in 1992 (59%) and in 1997 (55%) was a combination of medication with cognitive behavioral therapy. The vast majority of the expert panel included a medication in their recommendations--91% in 1992 and 90% in 1997. Experts recommending a medication for panic in 1992 chose as first-line treatment a benzodiazepine (35%), a selective serotonin reuptake inhibitor (SSRI, 7%), an older antidepressant (33%), or a combination of medications (25%), principally a benzodiazepine plus an older antidepressant (19%). In 1997, fewer chose a benzodiazepine (15%) or an older antidepressant (11%) alone, whereas 33% chose an SSRI alone. More experts chose a combination of medications in 1997 (39%), and the increase was attributable mainly to the choice of a benzodiazepine plus an SSRI (17%). Overall, there was only a small decline in recommendations for benzodiazepines, whereas the increased choice of SSRIs came largely at the expense of the older antidepressants. As second-line medications for panic should their first-line choice fail, the experts in 1997 recommended a benzodiazepine (7%), an SSRI (15%), an older antidepressant (28%), or a combination of medications (50%), most often a benzodiazepine plus an older antidepressant (21%) or a benzodiazepine plus an SSRI (17%). (Experts were not asked to recommend second-line treatment in 1992). Thus, in case of unsatisfactory response, the experts' choices shifted from benzodiazepines and SSRIs alone toward the older antidepressants alone or combinations of an antidepressant plus a benzodiazepine. This report concluded that combined cognitive behavioral therapy plus medication was highly favored by the experts as the initial treatment strategy for panic disorder. Over the past 5 years, SSRIs displaced older antidepressants as the experts' choice for first-line pharmacotherapy of panic disorder. In case of an unsatisfactory response, the experts more often recommended an older antidepressant or a combination of an antidepressant plus a benzodiazepine. According to the experts' judgments, the benzodiazepines, especially combined with an antidepressant, remain mainstays of pharmacotherapy for panic disorder.