Field Testing the "Avoid the Needle" Intervention for Persons at Risk for Transitioning to Injecting Drug Use in Tallinn, Estonia and New York City, USA.

This study aimed to field tested the "Avoid the Needle" (AtN) intervention to reduce transitions from non-injecting to injecting drug use in two different epidemiological settings. Respondent driven sampling was used to recruit current non-injecting drug users (NIDUs) in Tallinn, Estonia in 2018-19 and in New York City (NYC) in 2019-20. Both persons who had never injected and persons who had previously injected but not in the last 6 months were eligible; a structured interview was administered, a blood sample collected, and the intervention administered by trained interventionists. We recruited 19 non-injectors from Tallinn and 140 from NYC. Participants in Tallinn were younger and had begun using drugs at earlier ages than participants in NYC. The primary drugs used in Tallinn were amphetamine, fentanyl, and opioid analgesics, while in NYC they were heroin, cocaine, speedball, and fentanyl. Six-month follow-up data were obtained from 95% of participants in Tallinn. The study was interrupted by COVID-19 lockdown in NYC, but follow-up data were obtained from 59% of participants. There were minimal transitions to injecting: 1/18 in Tallinn and 0/83 in NYC. There were significant declines in the frequencies of using readily injectable drugs (fentanyl, amphetamine, heroin, cocaine) from baseline to follow-up in both sites (Cochran-Armitage tests for trend, χ2 = 21.3, p < 0.001 for New York City; and χ2 = 3.9, p = 0.048 for Tallinn). Reducing transitions into injecting is a potentially very important method for reducing HIV transmission and other harms of drug use. Further investigation and implementation of AtN type interventions is warranted.

Implementing an Updated "Break the Cycle" Intervention to Reduce Initiating Persons into Injecting Drug Use in an Eastern European and a US "opioid epidemic" Setting.

We tested the hypothesis that an updated "Break the Cycle" (BtC) intervention, based in social cognitive theory and motivational interviewing, would reduce the likelihood that current persons who inject drugs (PWID) would assist persons who do not inject drugs (non-PWID) with first injections in Tallinn, Estonia and Staten Island, New York City. 402 PWID were recruited, a baseline interview covering demographics, drug use, and assisting non-PWID with first drug injections was administered, followed by BtC intervention. 296 follow-up interviews were conducted 6 months post-intervention. Percentages assisting with first injections declined from 4.7 to 1.3% (73% reduction) in Tallinn (p < 0.02), and from 15 to 6% (60% reduction) in Staten Island (p < 0.05). Persons assisted with first injections declined from 11 to 3 in Tallinn (p = 0.02) and from 32 to 13 in Staten Island. (p = 0.024). Further implementation research on BtC interventions is urgently needed where injecting drug use is driving HIV/HCV epidemics and areas experiencing opioid epidemics.

Prevalence of injecting drug use in Estonia 2010-2015: a capture-recapture study.

BACKGROUND: It has been observed in an earlier study that the number of people who inject drugs (PWID) in Estonia is declining. We provide nationwide estimates of the number of PWID in Estonia for years 2010-2015 and compare different modelling strategies to minimise over-coverage-induced bias in capture-recapture estimates. METHODS: We obtained data from the Estonian Causes of Death Registry (DR) for opioid-related deaths, the Estonian Health Insurance Fund (HIF) for opioid-related overdose and drug dependence treatment episodes, and the Estonian Police and Border Guard Board (PB) drug-related misdemeanours. Datasets were linked by identifier based on sex, date of birth, and initials; a capture-recapture method was used to estimate the number of PWID aged 15 or more, each year from 2010 to 2015. Log-linear regression maximum likelihood (ML) and Bayesian methods were used; over-coverage of police data was accounted for. RESULTS: The annual population size estimates of the number of PWID (aged 15 and over) varied from 6000 to 17,300 (ML estimates not accounting for over-coverage of PB) to 1500-2300 (Bayesian estimates accounting for over-coverage). Bayesian estimates indicated a slight decrease in the number of PWID, and the median estimates were > 2000 in years 2010-2012 and < 1800 in years 2013-2015. CONCLUSIONS: Over-coverage of a registry can have a great impact on the estimates of the size of the target population. Bayesian estimates accounting for this over-coverage may provide better estimates of the target population size.

Effects of Counselling on Adherence to Antiretroviral Treatment Among People with HIV in Estonia: A Randomized Controlled Trial.

To assess the efficacy of an education- and strengths-based counselling programme to promote antiretroviral therapy (ART) adherence in a cohort of HIV-infected individuals with high prevalence of injection drug use in Estonia. Parallel-group randomized (1:1) controlled trial (RCT). Adults receiving ART in two clinics were followed for 12 months. The trial compared: (i) an intervention (three sessions) incorporated into routine clinic visits, providing education about HIV, ART, the role of adherence, and tailoring regimen to daily routines using problem-solving skills to address adherence barriers versus (ii) usual care (control). Primary and secondary outcomes were self-reported ART adherence (3-day recall) and viral load (respectively). 519 patients were randomized and 82% completed the study. Recent optimal ART adherence (3-day recall ≥95%) was reported by 75.6% in the intervention group and 72.9% of controls at baseline and 76.7% and 67.5%, respectively, at 12 months (RR 1.14, 95% CI 1.00-1.28; adjusted RR 1.13, 95% CI 1.00-1.27). There was no difference in the proportion of patients with undetectable viral load. At 12 months the intervention group reported significantly higher perceptions of ART necessity versus ART concerns [mean ART necessity-concerns differential: intervention group 1.32 (SD 1.22) vs control group 1.08 (SD 1.12); p = 0.048]. All-cause mortality among study participants was 27.7 per 1000 person years (95% CI 15.6-44.8). A brief, clinic-based adherence intervention alone may assist with adherence but lacks impact on viral load at 12 months.

Cigarette smoking and smoking-attributable diseases among Estonian physicians: a cross-sectional study.

BACKGROUND: Smoking is a risk factor for several diseases. Physicians are role models for their patients. Physicians who smoke underestimate the health risks of smoking and may be less likely to offer advice to help their patients to quit. The aim of this study was to: provide an overview of smoking behaviour among Estonian physicians; assess the relationship between smoking and ischaemic heart disease (IHD), chronic bronchitis (CB), and lung emphysema (LE); and estimate fractions of prevalences of the three diseases attributable to smoking. METHODS: Self-administered questionnaires were sent to practising physicians (n = 5666) in Estonia in 2014. Prevalence of smoking and relative risks for IHD, CB and LE as well as the risks of IHD, CB and LE attributable to smoking were calculated by age and sex. Post-stratification was used to compensate non-response. RESULTS: There were 535 male and 2404 female physicians participating. The prevalence of daily smoking was 12.4% (95% CI 10.4-14.4%) among men and 5.0% (95% CI 4.4-5.6%) among women. Mean duration of smoking among male and female daily smokers was 28.6 (95% CI 26.1-31.1) and 28.6 (95% CI 27.1-30.2) years. Compared to lifelong non-smokers, the age-adjusted risk for IHD was 1.29 times (95% CI 0.88-1.89) higher for men, but 1.69 times (95% CI 1.17-2.40) lower for all women who have ever smoked. The risk for CB was 2.29 (95% CI 1.30-4.03) times higher for smokers among men and, 1.32 (95% CI 0.95-1.82) among women; the risk ratio for LE was 4.92 (95% CI 1.14-21.1) among men and 2.45 (95% CI 0.63-9.52) among women. The smoking-attributable risk for IHD was 3.2% (95% CI 2.3-4.1%) among men and - 0.1% (95% CI -0.7-0.4%) among women; for CB 6.9% (95% CI 6.0-7.8%) and 4.2% (95% CI 3.5-4.8%); and for LE 18.8% (95% CI 17.0-22.5%) and 22.6% (95% CI 18.5-26.9%), respectively. CONCLUSION: Prevalence of daily smoking was relatively low among Estonian physicians (and twice lower among female physicians). The risk attributable to smoking was higher for LE and CB than for IHD.

Another frontier for harm reduction: contraceptive needs of females who inject drugs in Estonia, a cross-sectional study.

BACKGROUND: Despite increasing contraceptive availability, unintended pregnancy remains a global problem. Developing strategies to reverse this trend and increasing occurrence of withdrawal syndrome among newborn children of females currently injecting drugs warrants special attention. The knowledge base on the uptake of effective contraception among females who inject drugs (FWID) is scant. We aimed to examine the prevalence of and factors associated with the use of non-condom contraceptives among sexually active FWID with the focus on effective contraception. METHODS: In a series of cross-sectional studies (2007-2013), 265 current FWID were recruited through respondent-driven sampling (RDS), interviewed, and tested for HIV. RDS weights were used to estimate the prevalence of effective contraception (hormonal contraception, intrauterine device, sterilization) use in the last 6 months. RESULTS: Of the sexually active women with main partners (n = 196) 4.8% (95% CI 2.3-9.7) were using effective contraception, 52.7% (95% CI 42.5-62.7) less-effective or no contraception. 42.5% (95% CI 32.7-52.9) relied on condoms for contraception. The odds for using effective contraception were higher among women with > 10 years of education (OR 7.29, 95% CI 1.4-38.8). None of the women lacking health insurance (n = 84) were using effective contraception. CONCLUSIONS: The very low coverage with effective contraception highlights the need to improve contraceptive services for FWID. Reproductive health service including contraception should be considered essential components of harm reduction and of comprehensive prevention and care for HIV among persons who use drugs.

Personality traits and escitalopram treatment outcome in major depression.

BACKGROUND: Selective serotonin re-uptake inhibitors (SSRI) have proven to be effective in treatment of depression. Still, treatment efficacy varies significantly from patient to patient and about 40% of patients do not respond to initial treatment. Personality traits have been considered one source of variability in treatment outcome. AIM: Current study aimed at identifying specific personality traits that could be predictive of treatment response and/or the dynamics of symptom change in depressive patients. METHOD: In a sample of 132 outpatients with major depressive disorder (MDD) treated with an SSRI-group antidepressant escitalopram, the Swedish universities Scales of Personality (SSP) were used in order to find predictive personality traits. For the assessment of the severity of depressive symptoms and the improvement rates, the Hamilton Depression Scale (HAM-D) and Montgomery-Åsberg Depression Rating Scale (MADRS) were used. RESULTS: Escitalopram-treated MDD patients with higher social desirability achieved more rapid decrease in symptom severity. None of the studied traits predicted the end result of the treatment. CONCLUSION: The findings suggest that specific personality traits may predict the trajectory of symptom change rather than the overall improvement rate.

The impact of hip fracture on mortality in Estonia: a retrospective population-based cohort study.

BACKGROUND: Estimates of hip fracture mortality in Eastern Europe are scarce. We aimed to estimate the magnitude and duration of excess mortality after hip fracture in Estonia. METHODS: Retrospective, population-based 10-year study of persons aged ≥50 in two cohorts: with hip fracture and an age- and sex-matched (in a 1:4 ratio) random sample from the national health insurance fund database for comparison. Cumulative risks, excess risks and relative risks of death were estimated using Poisson regression with 95% bootstrap confidence intervals (CI). Risks were adjusted for age and Charlson comorbidity index. RESULTS: We identified 8298 (2383 men, 5915 women) incident hip fracture patients from 2005 to 2013 and 33,191 (9531 men, 23,660 women) individuals for the reference group. 5552 (1564 men, 3988 women) cases and 14,037 (3514 men, 10,523 women) reference individuals died during the 10-year follow-up period. Among hip fracture patients we observed a pronounced and durable excess risk of death that was highest within 3-6 months after fracture and persisted for the full 10-year follow-up period. After adjustment for age and Charlson index, hip fracture was associated with a 21.1% (95% CI 20.0-22.5%) 10-year cumulative excess risk of death (RR 1.37, 95% CI 1.35-1.40). We found a high immediate excess risk of death in older age groups (≥80 years) and gradually accumulating excess risk in younger age groups (50-79 years). The excess risk was more pronounced among men than women. CONCLUSIONS: By the end of the 10-year follow-up, 1 in 4 deaths in the hip fracture group was attributable to the hip fracture. The results indicate a high attributable impact of hip fracture as an independent risk factor for death.

Association between personality traits and Escitalopram treatment efficacy in panic disorder.

BACKGROUND: There is strong evidence to suggest that personality factors may interact with the development and clinical expression of panic disorder (PD). A greater understanding of these relationships may have important implications for clinical practice and implications for searching reliable predictors of treatment outcome. AIMS: The study aimed to examine the effect of escitalopram treatment on personality traits in PD patients, and to identify whether the treatment outcome could be predicted by any personality trait. METHOD: A study sample consisting of 110 outpatients with PD treated with 10-20 mg/day of escitalopram for 12 weeks. The personality traits were evaluated before and after 12 weeks of medication by using the Swedish universities Scales of Personality (SSP). RESULTS: Although almost all personality traits on the SSP measurement were improved after 12 weeks of medication in comparison with the baseline scores, none of these changes reached a statistically significant level. Only higher impulsivity at baseline SSP predicted non-remission to 12-weeks treatment with escitalopram; however, this association did not withstand the Bonferroni correction in multiple comparisons. LIMITATIONS: All patients were treated in a naturalistic way using an open-label drug, so placebo responses cannot be excluded. The sample size can still be considered not large enough to reveal statistically significant findings. CONCLUSIONS: Maladaptive personality disposition in patients with PD seems to have a trait character and shows little trend toward normalization after 12-weeks treatment with the antidepressant, while the association between impulsivity and treatment response needs further investigation.

People living with HIV in Estonia: engagement in HIV care in 2013.

Estonia had the highest rate of newly diagnosed human immunodeficiency virus (HIV) cases in the European Union (24.6/100,000) and an estimated adult HIV prevalence of 1.3% in 2013. HIV medical care, including antiretroviral therapy (ART), is free of charge for people living with HIV (PLHIV). To maximise the health benefits of HIV treatment, universal access should be achieved. Using data from surveillance and administrative databases and the treatment cascade model, we assessed the number of people infected with HIV, diagnosed with HIV, linked to HIV care, retained in HIV care, on ART, and with suppressed viral load (HIV-RNA: < 200 copies/mL). We identified that about one quarter of the 8,628 HIV-positive people estimated to live in Estonia in 2013 had not been diagnosed with HIV, and another quarter, although aware of their HIV-positive serostatus, had not accessed HIV medical care. Although altogether only 12-15% of all PLHIV in Estonia had achieved viral suppression, the main gap in HIV care in Estonia were the 58% of PLHIV who had accessed HIV medical care at least once after diagnosis but were not retained in care in 2013.

Combined prevention for persons who inject drugs in the HIV epidemic in a transitional country: the case of Tallinn, Estonia.

The study was undertaken to assess the potential effectiveness of combined HIV prevention on the very high seroprevalence epidemic among persons who inject drugs (PWID) in Tallinn, Estonia, a transitional country. Data from community-based cross-sectional (respondent-driven sampling) surveys of PWID in 2005, 2007, 2009, and 2011 were used together with mathematical modeling of injection-associated HIV acquisition to estimate changes in injection-related HIV incidence during these periods. Utilization of one, two, or three of the interventions available in the community (needle and syringes exchange program, antiretroviral treatment [ART], HIV testing, opioid substitution treatment) was reported by 42.5%, 30.5%, and 11.5% of HIV+ and 34.7%, 36.4%, and 5.7% of HIV- PWIDs, respectively, in 2011. The modeling results suggest that the combination of needle/syringe programs and provision of ART to PWID in Tallinn substantially reduced the incidence of HIV infection in this population, from an estimated 20.7/100 person-years in 2005 to 7.5/100 person-years in 2011. In conclusion, combined prevention targeting HIV acquisition and transmission-related risks among PWID in Tallinn has paralleled the downturn of the HIV epidemic in this population.

Non-fatal overdoses and related risk factors among people who inject drugs in St. Petersburg, Russia and Kohtla-Järve, Estonia.

BACKGROUND: This study seeks to identify the prevalence of, and risk factors associated with, non-fatal overdose among people currently injecting drugs (PWID) in St. Petersburg (Russia) and in Kohtla-Järve (Estonia). METHODS: Five hundred eighty-eight study participants in Kohtla-Järve (in 2012) and 811 in St. Petersburg (in 2012-2013) were recruited using respondent driven sampling for interviewing and HIV testing. RESULTS: Three-quarters (76%) of the current PWID were male. Participants from St. Petersburg were older (mean age 32.1 vs. 29.6 years, p < 0.0001) and reported a longer average duration of injecting drugs (mean duration: 13.3 vs. 10.9 years, p < 0.0001). Main drugs injected were opioids (fentanyl in Kohtla-Järve, heroin in St Petersburg). HIV prevalence was 63% (95% CI 59-67%) in Kohtla-Järve and 56% (95% CI 52-59%) in St. Petersburg. Two thirds of the PWID in Kohtla-Järve and St. Petersburg reported ever having experienced a drug overdose involving loss of consciousness or stopping breathing. In Kohtla-Järve, 28% (95% CI 24-31%) of participants and, in St Petersburg, 16% (95% CI 14-19%) of participants reported an overdose within the previous 12 months. Characteristics of injection drug use practice (longer duration of injection drug use, main drug injected), correlates of high-risk injection behaviour (higher injecting frequency, sharing), and problem alcohol use were associated with the risk of overdose within the previous 12 months. The significant factors effects did not differ between the sites. CONCLUSIONS: PWID are at high risk for overdose. Effective overdose prevention efforts at the public health scale are therefore warranted.

Nationwide study on development and validation of a risk prediction model for CIN3+ and cervical cancer in Estonia.

Transitioning to an individualized risk-based approach can significantly enhance cervical cancer screening programs. We aimed to derive and internally validate a prediction model for assessing the risk of cervical intraepithelial neoplasia grade 3 or higher (CIN3+) and cancer in women eligible for screening. This retrospective study utilized data from the Estonian electronic health records, including 517,884 women from the health insurance database and linked health registries. We employed Cox proportional hazard regression, incorporating reproductive and medical history variables (14 covariates), and utilized the least absolute shrinkage and selection operator (LASSO) for variable selection. A 10-fold cross-validation for internal validation of the model was used. The main outcomes were the performance of discrimination and calibration. Over the 8-year follow-up, we identified 1326 women with cervical cancer and 5929 with CIN3+, with absolute risks of 0.3% and 1.1%, respectively. The prediction model for CIN3 + and cervical cancer had good discriminative power and was well calibrated Harrell's C of 0.74 (0.73-0.74) (calibration slope 1.00 (0.97-1.02) and 0.67 (0.66-0.69) (calibration slope 0.92 (0.84-1.00) respectively. A developed model based on nationwide electronic health data showed potential utility for risk stratification to supplement screening efforts. This work was supported through grants number PRG2218 from the Estonian Research Council, and EMP416 from the EEA (European Economic Area) and Norway Grants.

The epidemiological and economic impact of a quadrivalent human papillomavirus (hpv) vaccine in Estonia.

BACKGROUND: This analysis assessed the epidemiological and economic impact of quadrivalent human papillomavirus (HPV4: 6/11/16/18) vaccination in Estonia. METHODS: A dynamic transmission model was used to assess the epidemiological and economic impact of the routine vaccination of 12-year-old girls with a HPV4 vaccine in preventing cervical cancer, cervical intraepithelial neoplasia (CIN) grades 1, 2 and 3 and genital warts. RESULTS: The model projected that at year 100, HPV4 vaccination would lead to a reduction of HPV 16/18 related cervical cancer incidence and deaths by over 97% and the incidence of HPV 6/11 related genital warts among Estonian women and men by over 94% and 81%, respectively. The incremental cost-effectiveness ratio of the HPV4 vaccination strategy was € 4,889 per QALY gained over a time horizon of 100 years. CONCLUSIONS: Routine vaccination of 12-year-old girls with HPV4 vaccine appears to be cost-effective in Estonia, in addition to providing both short term and long term health gains.

Incidence of cervical intraepithelial neoplasia in Estonia.

OBJECTIVE: This study aimed to assess the incidence of cervical intraepithelial neoplasia (CIN) by grade (CIN 1, CIN 2, CIN 3) and age in Estonia (a country with less developed cervical cancer screening program and high cervical cancer incidence). MATERIALS AND METHODS: This descriptive study uses data from a health insurance fund covering the whole country to estimate the incidence of CIN by grade. CIN case definition was based on specific diagnostic procedures (biopsy, pathological diagnosis, and colposcopy) and/or treatment procedures (excision, local destructive therapy, conization, and hysterectomy) with the CIN-specific diagnosis code (International Statistical Classification of Diseases, 10 Revision) reported on health care claims. Age-specific incidence rates were calculated together with the 95% CIs. Main outcome measure includes CIN grade-specific incidence rate per 1,000 women. RESULTS: The estimates for CIN incidence per 1,000 women range from 0.68 to 2.83 for CIN 1, 0.63 to 1.24 for CIN 2, and 0.13 to 0.53 for CIN 3 for narrow (biopsy/pathological diagnosis based) and broad (any CIN-specific diagnostic procedure/treatment based) case definition criteria, respectively. CONCLUSIONS: Our estimates for cervical dysplasia disease frequency and age distribution are in line with those from other developed countries. Administrative health care resources (such as health insurance fund data) are a valuable source for health research.

Adapted "Break the Cycle for Avant Garde" intervention to reduce injection assisting and promoting behaviours in people who inject drugs in Tallinn, Estonia: A pre- post trial.

In the context of established and emerging injection drug use epidemics, there is a need to prevent and avert injection drug use. We tested the hypothesis that an individual motivation and skills building counselling, adapted and enhanced from Hunt's Break the Cycle intervention targeting persons currently injecting drugs would lead to reduction in injection initiation-related behaviours among PWID in Tallinn, Estonia. For this quasi-experimental study, pre-post outcome measures included self-reported promoting behaviours (speaking positively about injecting to non-injectors, injecting in front of non-injectors, offering to give a first injection) and injection initiation behaviours (assisting with or giving a first injection) during the previous 6 months. Of 214 PWID recruited, 189 were retained (88.3%) for the follow-up at 6 months. The proportion of those who had injected in front of non-PWID significantly declined from 15.9% to 8.5%, and reporting assisting with 1st injection from 6.4% to 1.06%. Of the current injectors retained in the study, 17.5% reported not injecting drugs at the follow up. The intervention adapted for the use in the setting of high prevalence of HIV and relatively low prevalence of injection assisting, tested proved to be effective and safe.

Antiretroviral therapy (ART) adherence and correlates to nonadherence among people on ART in Estonia.

There are little data on antiretroviral therapy (ART) adherence among patients in Eastern Europe, despite the high incidence of HIV infection and the growing number of HIV-infected individuals who are being prescribed ART. The aim of this study was to measure rates of adherence to ART and factors associated with nonadherence among patients receiving care at an outpatient HIV clinic in Estonia. The study was based on cross-sectional data from a convenience sample of 144 patients receiving outpatient HIV care. Data were obtained via interviewer-administered surveys and data abstraction from clinical records. Adherence was measured from a 3-day patient self-report. Among 144 participants (mean age 33.8 years), two-thirds (63%) had been infected with HIV through intravenous drug use. Most (74%) were co-infected with hepatitis C (HCV). Perfect adherence over the last 3 days was commonly reported (88% [95% CI 81-92%]) with nonperfect adherence associated with greater concerns about the potential adverse consequences of taking ART (adjusted odds ratio [AOR] 4.8, 95% CI 1.2-34.0) and average (versus good/very good) self-reported health status (AOR 4.7, 95% CI 1.2-31.4). Self-reported ART adherence in this sample of Estonian HIV-positive patients in clinical care was similar to rates observed in Western Europe and other developed countries. Results suggest that adherence education and support may be most helpful if they specifically target the development of positive beliefs, reduction of negative expectancies towards ART.

A Multistage Process Model of How a Person Who Currently Injects Drugs Comes to Assist Persons Who Do not Inject with Their First Injections.

Injecting drugs for the first time almost always requires assistance from an experienced person who injects drugs (PWID). While there has been moderate amount of research on PWID who assist with first injections, most of this research has focused on identifying characteristics of PWID who assist with first injections. We do not have a formal model that describes how the minority of PWID come to assist do so, while the majority never assist. Through comparison of persons who did or did not recently assist with first injections using data from PWID in Tallinn, Estonia (N = 286) and Staten Island, New York City (N = 101), we developed a formal multi-stage model of how PWID come to assist with first injections. The model had a primary pathway 1) of engaging in "injection promoting" behaviors, 2) being asked to assist, and 3) assisting. Statistical testing using odds ratios showed participation in each stage was strongly associated with participation in the next stage (all odds ratios >3.0) and the probabilities of assisting significantly increased with participation in the successive stages. We then used the model to compare engagement in the stages pre-vs. post participation in an intervention, and to compare persons who recently assisted to persons who had assisted in the past but had not recently assisted and to persons who had never assisted. Advantages of a formal model for how current PWID come to assist with first injections include: facilitating comparisons across different PWID populations and assessing strengths and limitations of interventions to reduce assisting with first injections.

Evaluating recruitment among female sex workers and injecting drug users at risk for HIV using respondent-driven sampling in Estonia.

Few recent publications have highlighted theoretical and methodological challenges using respondent-driven sampling (RDS). To explore why recruitment with RDS may work in some populations and not in others, we assess the implementation of RDS to recruit female sex workers (FSWs) and injection drug users (IDUs) into a human immunodeficiency virus biological and risk behavior survey in Tallinn, Estonia. Recruitment of FSWs was slower and more challenging than that of IDUs. The IDU study recruited 350 participants within 7 weeks, while the FSW study recruited 227 participants over 28 weeks. Implementation modifications that did not negatively impact key RDS theoretical and methodological requirements were used to improve recruitment during the FSW study. We recommend that all RDS studies include a formative research process to involve the participation of target populations and key persons associated with these populations in the study planning and throughout the implementation processes to improve recruitment from the outset and to respond to poor recruitment during data collection.