•Researchers must overcome multiple barriers in recruiting and retaining research participants living in conditions of vulnerability.•A comprehensive recruitment strategy that combines various elements tailored to vulnerable populations is required.•Most studies describing recruitment and retention of participants from vulnerable populations pertain to clinical settings.•This study describes strategies and challenges in recruiting participants through community organizations.•This paper provides recommendations on recruiting and retaining people living in conditions of extreme vulnerability.

BACKGROUND: Administering patient-reported outcome measures (PROMs) by text message may improve response rate in hard-to-reach populations. This study explored cultural acceptability of PROMs and compared measurement equivalence of the EQ-5D-3L administered on paper and by text message in a rural South African setting.
METHODS: Participants with upper or lower limb orthopaedic pathology were recruited. The EQ-5D was administered first on paper and then by text message after 24 h and 7 days. Differences in mean scores for paper and text message versions of the EQ-5D were evaluated. Test-retest reliability between text message versions was evaluated using Intraclass Correlation Coefficients (ICCs).
RESULTS: 147 participants completed a paper EQ-5D. Response rates were 67% at 24 h and 58% at 7 days. There were no differences in means between paper and text message responses for the EQ-5D Index (p = 0.95) or EQ-5D VAS (p = 0.26). There was acceptable agreement between the paper and 24-h text message EQ-5D Index (0.84; 95% Confidence Interval (CI) 0.78-0.89) and EQ-5D VAS (0.73; 95% CI 0.64-0.82) and acceptable agreement between the 24-h and 7-day text message EQ-Index (0.72; CI 0.62-0.82) and EQ-VAS (0.72; CI 0.62-0.82). Non-responder traits were increasing age, Xhosa as first language and lower educational levels.
CONCLUSIONS: Text messaging is equivalent to paper-based measurement of EQ-5D in this setting and is thus a viable tool for responders. Non-responders had similar socioeconomic characteristics and attrition rates to traditional modes of administration. The EQ-5D by text message offers potential clinical and research uses in hard-to-reach populations.

In response to a cholera outbreak among mobile, difficult-to-reach fishermen on Lake Chilwa, Malawi in 2016, a novel vaccine distribution strategy exploited the proven vaccine thermostability. Fishermen, while taking the first vaccine dose under supervision, received the second dose in a sealed bag, and were told to drink it two weeks later. This study assessed short-term vaccine protection of this strategy.
Patients with diarrhoea admitted to health facilities around lake were interviewed and a stool sample collected for PCR testing. Vaccine effectiveness was assessed in a case-control test-negative design by comparing cases (PCR-positive for V. cholerae O1) and controls (patients with diarrhoea but PCR-negative) and with the screening method that compared the proportions of vaccinated among cholera cases versus the general fishermen population.
Of 145 study participants, 120 were fishermen living on the lake. Vaccine effectiveness at three-months was 90.0% [95%CI:38.8;98.4] among fishermen and 83.3% [95%CI: 20.8; 96.5] among all participants in the case-control test-negative design, and 97.5% [95%CI: 90.9;99.3] with the screening method.
This strategy was effective in providing short-term protection in fishermen against cholera. Further research is needed to determine the adding value of the second dose and to identify the optimal vaccination strategies for different contexts.

We evaluated the effectiveness of different recruitment strategies used in a study aimed at eliminating/reducing second-hand smoke (SHS) exposure in Dutch children 0-13 years of age with a high risk of asthma.
The different strategies include: 1) questionnaires distributed via home addresses, physicians or schools of the children; 2) cohorts from other paediatric studies; 3) physicians working in the paediatric field (family physicians, paediatricians and Youth Health Care (YHC) physicians); and 4) advertisements in a local newsletter, at child-care facilities, and day-care centres.
More than 42,782 families were approached to take part in the screening of which 3663 could be assessed for eligibility. Of these responders, 196 families met the inclusion criteria for the study. However, only 58 (one third) could be randomised in the trial, mainly because of no interest or time of the parents. The results showed that recruiting families who expose their children to SHS exposure is very challenging, which may be explained by lack of \'recognition\' or awareness that SHS occurs in homes. The presence of asthma in the family, respiratory symptoms in the children, and even incentives did not increase parental motivation for participation in the study.
The recruitment process for an intervention program addressing SHS exposure in children was considerably more challenging and time consuming than anticipated. Barriers at both a parents level and a doctor\'s level can be discriminated.

The burden of sexually transmitted infections (STIs), such as syphilis, is higher in low-income countries, with serious consequences and profound impact on sexual and reproductive health and human immunodeficiency virus (HIV) spread. Syphilis prevalence tend to be higher among people who misuse drugs than in the general population.
To assess syphilis and associated factors among polydrug users (PDU) in the city of Salvador, Northeast Brazil.
A cross-sectional study was conducted in 10 Brazilian cities between September and November 2009 using Respondent Driven Sampling (RDS). Participants answered an Audio Computer-Assisted Self Interview (ACASI) and were rapid tested for HIV and syphilis. We performed multivariable regression models for correlates of syphilis on Stata 10.0. Estimates were weighted by the inverse size of the individual social network size and homophily.
Mean age was 29.3 years (range: 18-62), 74.0% were males, and 89.8% were non-white. Syphilis prevalence was 16.6%. Females (adjwOR:2.14; 95%CI:1.09-4.20), individuals over 29 years old (adjwOR:4.44; 95%CI:2.41-8.19), those who exchanged sex for money or drugs (adjwOR:3.51; 95%CI:1.84-6.71), \"No/low\" self-perceived risk of HIV infection (adjwOR:5.13; 95%CI:1.36-19.37), and having nine or less years of education (adjwOR:2.92; 95%CI:1.08-7.88) were associated with syphilis.
One of the most pressing needs for syphilis prevention/control is the availability of rapid point-of-care diagnostic tests and treatment. Interventions should be tailored to PDU needs and their multiple burdens as shown in the present study, that may contribute to future studies aiming to better understand the relationships between drug use and syphilis.

Collecting data from hard-to-reach populations is a key challenge for research on poverty and other forms of extreme disadvantage. With data from the Boston Reentry Study (BRS), we document the extreme marginality of released prisoners and the related difficulties of study retention and analysis. Analysis of the BRS data yields three findings. First, released prisoners show high levels of \"contact insecurity,\" correlated with social insecurity, in which residential addresses and contact information change frequently. Second, strategies for data collection are available to sustain very high rates of study participation. Third, survey nonresponse in highly marginal populations is strongly nonignorable, closely related to social and economic vulnerability. The BRS response rate of 94% over a 1-y follow-up period allows analysis of hypothetically high nonresponse rates. In this setting, nonresponse attenuates regression estimates in analyses of housing insecurity, drug use, and unemployment. These results suggest that in the analysis of very poor and disadvantaged populations, methods that maximize study participation reduce bias and yield data that can usefully supplement large-scale household or administrative data collections.

Objective To evaluate the impact of a client-centered behavioral intervention (Brief Negotiated Interviewing) on mothers\' human papillomavirus (HPV) vaccine knowledge and vaccination initiation for their adolescent daughters. Methods We randomized mothers to intervention (n = 100) and control (n = 100) groups, and followed them over 12 months. Electronic medical records were reviewed to determine vaccination status. The primary outcome was receipt of the first vaccine. The secondary outcome was HPV vaccine knowledge among mothers. Results Brief Negotiated Interviewing intervention mothers demonstrated increased knowledge about HPV (pre/post mean score of 5 to 10 out of a possible 11; P < .001) and significantly higher mean knowledge scores (10 vs 6, P < .001) than control mothers. However, initiation and completion rates of the vaccine were not significantly different between groups. Conclusions Increasing HPV vaccine knowledge did not translate into increased vaccine uptake or completion of vaccination series. Future intervention must explore vaccine reminders to increase HPV vaccination rates.