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New paper on a network-centric analysis of the relationship between risk behaviors and HIV/HCV prevalence in Rural Puerto Rico

“Understanding differences in HIV/HCV prevalence according to differentiated risk behaviors in a sample of PWID in rural Puerto Rico.” Journal of Harm Reduction 13 (10): 1-7.
Roberto Abadie, Melissa Welch-Lazoritz, Camila Gelpi-Acosta, Juan Carlos Reyes, Ric Curtis, Kirk Dombrowski

Blood contained in needles and injection equipment has been identified as a vector for HIV and HCV transmission among people who inject drugs (PWID). Yet, there is often a wide discrepancy in prevalence for both viruses. While microbiological differences between viruses influence prevalence, other variables associated with the way drugs are acquired and used, also play a role.

Respondent-driven sampling (RDS) methods recruited a sample of 315 current intravenous drug users in rural Puerto Rico. Information about type and frequency of use, HIV and HVC risk behaviors (sharing needles, cookers, cotton, and water), sexual behaviors, and alcohol use was collected. HIV and HCV statuses were assessed via rapid antibody tests. T tests compare means of participants who tested positive (reactive) to those who tested negative. Logistic regression analyses were used to validate the association of the risk factors involved.

Tests showed a significant difference in HIV (6 %) and HCV (78.4 %) prevalence among a population of current PWID. The main risk behaviors in HCV transmission are the sharing of injection “works”, (e.g., cookers, cotton, and water). Sharing works occurred more than twice as often as the sharing of needles, and HCV+ and HCV? individuals reported the same needle sharing habits.

New paper describing innovations to the classical Network Scale-up Method for determining population size estimates

“Improving the Network Scale-Up Estimator: Incorporating Means of Sums, Recursive Back Estimation, and Sampling Weights.” PLoSOne 10(12): e0143406.
Patrick Habecker, Kirk Dombrowski, and Bilal Khan

Researchers interested in studying populations that are difficult to reach through traditional survey methods can now draw on a range of methods to access these populations. Yet many of these methods are more expensive and difficult to implement than studies using conventional sampling frames and trusted sampling methods. The network scale-up method (NSUM) provides a middle ground for researchers who wish to estimate the size of a hidden population, but lack the resources to conduct a more specialized hidden population study. Through this method it is possible to generate population estimates for a wide variety of groups that are perhaps unwilling to self-identify as such (for example, users of illegal drugs or other stigmatized populations) via traditional survey tools such as telephone or mail surveys—by asking a representative sample to estimate the number of people they know who are members of such a “hidden” subpopulation. The original estimator is formulated to minimize the weight a single scaling variable can exert upon the estimates. We argue that this introduces hidden and difficult to predict biases, and instead propose a series of methodological advances on the traditional scale-up estimation procedure, including a new estimator. Additionally, we formalize the incorporation of sample weights into the network scale-up estimation process, and propose a recursive process of back estimation “trimming” to identify and remove poorly performing predictors from the estimation process. To demonstrate these suggestions we use data from a network scale-up mail survey conducted in Nebraska during 2014. We find that using the new estimator and recursive trimming process provides more accurate estimates, especially when used in conjunction with sampling weights.


New paper on cyclic network organisms describing how growth produces evolutionary pressures towards the emergence of cellular heterogeneity

“Attractor-based obstructions to growth in homogenous cyclic Boolean automata.”Journal of Computer Science and System Biology 8(6): 341-353.
Bilal Khan, Yuri Kantor, Kirk Dombrowski,

We consider a synchronous Boolean organism consisting of N cells arranged in a circle, where each cell initially takes on an independently chosen Boolean value. During the lifetime of the organism, each cell updates its own value by responding to the presence (or absence) of diversity amongst its two neighbours’ values. We show that if all cells eventually take a value of 0 (irrespective of their initial values) then the organism necessarily has a cell count that is a power of 2. In addition, the converse is also proved: if the number of cells in the organism is a proper power of 2, then no matter what the initial values of the cells are, eventually all cells take on a value of 0 and then cease to change further. We argue that such an absence of structure in the dynamical properties of the organism implies a lack of adaptiveness, and so is evolutionarily disadvantageous. It follows that as the organism doubles in size (say from m to 2m) it will necessarily encounter an intermediate size that is a proper power of 2, and suffers from low adaptiveness. Finally we show, through computational experiments, that one way an organism can grow to more than twice its size and still avoid passing through intermediate sizes that lack structural dynamics, is for the organism to depart from assumptions of homogeneity at the cellular level.


New paper exploring the non-injection drug use among MSM and its role in Hepatitis-C incidence

“Hepatitis C. Virus Incidence among HIV+ Men Who Have Sex with Men: The Role of Non-Injection Drug Use.” Drug and Alcohol Dependence 146: e118-e201.
H. Hagan, J. Nuerer, A. E. Jordan, D. C. Des Jarlais, J. Wu, K. Dombrowski, B. Khan, S. Braithwaite, J. Kessler.

Outbreaks of hepatitis C virus (HCV) infection have been reported in HIV-positive men who have sex with men (MSM) in North America, Europe and Asia. Transmission is believed to be the result of exposure to blood during sexual contact. In those infected with HIV, acute HCV infection is more likely to become chronic, treatment for both HIV and HCV is more complicated and HCV disease progression may be accelerated. There is a need for systematic reviews and meta-analyses to synthesize the epidemiology, prevention and methods to control HCV infection in this population.
Eligible studies will include quantitative empirical data related to sexual transmission of HCV in HIV-positive MSM, including data describing incidence or prevalence, and associations between risk factors or interventions and the occurrence or progression of HCV disease. Care will be taken to ensure that HCV transmission related to injection drug use is excluded from the incidence estimates. Scientific databases will be searched using a comprehensive search strategy. Proceedings of scientific conferences, reference lists and personal files will also be searched. Quality ratings will be assigned to each eligible report using the Newcastle–Ottawa scale. Pooled estimates of incidence rates and measures of association will be calculated using random effects models. Heterogeneity will be assessed at each stage of data synthesis.
HIV-positive MSM are a key HCV-affected population in the US and other high-income countries. This review seeks to identify modifiable risk factors and settings that will be the target of interventions, and will consider how to constitute a portfolio of interventions to deliver the greatest health benefit. This question must be considered in relation to the magnitude of HCV infection and its consequences in other key affected populations, namely, young prescription opioid users who have transitioned to illicit opiate injection, and older injection drug users among whom HCV prevalence and incidence are extremely high. This review is part of a series of systematic reviews and meta-analyses that will synthesize the evidence across all these population groups and develop recommendations and decision tools to guide public health resource allocation.


New paper on Hispanic immigrant victims of violence seeks to determine predictors of police reporting using a network-centric approach

“Predictors of police reporting among Hispanic immigrant victims of violence.” Race and Justice 5(3): 235-258.  2015
Dane Hautala, Kirk Dombrowski, and Anthony Marcus.

The purpose of this study was to examine predictors of police reporting among Hispanic immigrant victims of violence. A sample of 127 Hispanic immigrants was generated through a chain-referral procedure in the city of Hempstead, New York. Participants were asked about their most recent victimization experiences, and detailed information was collected on up to three incidents. The analyses were based on a total of 214 separate victimization incidents, one third of which were reported to the police. Logistic regression analyses indicated that serious injury, multiple-victim incidents, and perceptions of discrimination increase the odds of a police report. Moreover, incidents involving a Black primary assailant were less likely to be reported to the police than incidents involving an assailant perceived to be of Hispanic origin. Supplementary analyses suggested that this latter relationship may be contingent upon the type of crime and the victim’s relationship with the assailant. At the policy level, these findings call into question assumptions about very recent immigrants being too socially isolated and distrustful of law enforcement to sustain robust reporting levels, as well as pointing to encouraging possibilities for productive engagement between police and Hispanic immigrant populations.