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ABSTRACT: PURPOSE: We examined the cross-sectional and longitudinal association between social network characteristics and street youths' shelter use, a determinant of health outcomes for homeless youth. METHODS: We analyzed interview data from 138 street youth recruited through venue-based sampling in San Francisco, to assess the cross-sectional relationship between shelter use in youths' social networks and youths' reported shelter use. We also assessed the relationship between baseline network shelter use and shelter use at 6-month follow-up. RESULTS: Low proportions of street youth reported shelter use at baseline (38%) and follow-up (29.6%). Twenty-nine (26.9%) youth were in networks with shelter users at baseline, compared with 17 youth (15.7%) at follow-up. In cross-sectional analysis, youth in networks with shelter users had 5-fold increased odds of reporting shelter use (OR: 5.86, p = .006). A 1-person increase in the number of network shelter users was associated with 2-fold increased odds of youths' shelter use (OR: 2.16, p = .02). In longitudinal analysis, youth in networks with shelter users at baseline had nearly 5-fold increased odds of shelter use at follow-up (OR: 4.95, p = .01). A 1-person increase in the number of network shelter users at baseline was associated with 3-fold increased odds of shelter use at follow-up (OR: 3.15, p = .004). CONCLUSION: Shelter users seem to cluster together. Shelter use by extended network members was associated with increased odds of youths' own shelter use. Understanding how network behaviors influence street youths' health-related behaviors, such as shelter use, could inform network-based interventions encouraging service uptake among marginalized and hard-to-reach street youth populations.
Journal of Adolescent Health 06/2013; · 3.33 Impact Factor
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ABSTRACT: In a largely rural region of North Carolina during 1998-2002, outbreaks of heterosexually transmitted syphilis occurred, tied to crack cocaine use and exchange of sex for drugs and money. Sexual partnership mixing patterns are an important characteristic of sexual networks that relate to transmission dynamics of sexually transmitted infections (STIs).
Using contact tracing data collected by disease intervention specialists, we estimated Newman assortativity coefficients and compared values in counties experiencing syphilis outbreaks to nonoutbreak counties, with respect to race/ethnicity, race/ethnicity and age, and the cases' number of social/sexual contacts, infected contacts, sex partners, and infected sex partners, and syphilis disease stage (primary, secondary, early latent).
Individuals in the outbreak counties had more contacts and mixing by the number of sex partners was disassortative in outbreak counties and assortative nonoutbreak counties. Although mixing by syphilis disease stage was minimally assortative in outbreak counties, it was disassortative in nonoutbreak areas. Partnerships were relatively discordant by age, especially among older white men, who often chose considerably younger female partners.
Whether assortative mixing exacerbates or attenuates the reach of STIs into different populations depends on the characteristic/attribute and epidemiologic phase. Examination of sexual partnership characteristics and mixing patterns offers insights into the growth of STI outbreaks that complement other research methods.
Sexually transmitted diseases 01/2011; 38(5):378-84. · 2.58 Impact Factor
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The Lancet 05/2010; 375(9729):1872; author reply 1873. · 38.28 Impact Factor
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ABSTRACT: A population-based sexual network study was used to identify sexual network structures associated with sexually transmitted infection (STI) risk, and to evaluate the degree to which the use of network-level data furthers the understanding of STI risk.
Participants (n = 655) were from the baseline and 12-month follow-up waves of a 2001-2 population-based longitudinal study of sexual networks among urban African-American adolescents. Sexual network position was characterised as the interaction between degree (number of partners) and two-reach centrality (number of partners' partners), resulting in the following five positions: confirmed dyad, unconfirmed dyad, periphery of non-dyadic component, centre of star-like component and interior of non-star component. STI risk was measured as laboratory-confirmed infection with gonorrhoea and/or chlamydia.
Results of logistic regression models with generalised estimating equations showed that being in the centre of a sexual network component increased the odds of infection at least sixfold compared with being in a confirmed dyad. Individuals on the periphery of non-dyadic components were nearly five times more likely to be infected than individuals in confirmed dyads, despite having only one partner. Measuring network position using only individual-based information led to twofold underestimates of the associations between STI risk and network position.
These results demonstrate the importance of measuring sexual network structure using network data to fully capture the probability of exposure to an infected partner.
Sexually transmitted infections 09/2009; 85(7):493-8. · 2.18 Impact Factor
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AIDS (London, England) 08/2008; 22(11):1377; author reply 1378-9. · 4.91 Impact Factor
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ABSTRACT: BACKGROUND:Social network analysis (SNA) is an innovative approach to the collection and analysis of infectious disease transmission data. We studied whether this approach can detect patterns of Mycobacterium tuberculosis transmission and play a helpful role in the complex process of prioritizing tuberculosis (TB) contact investigations.
METHODS:We abstracted routine demographic and clinical variables from patient medical records and contact interview forms. We also administered a structured questionnaire about places of social aggregation to TB patients and their contacts. All case-contact, contact-contact, case-place, and contact-place dyads (pairs and links) were considered in order to analyze the structure of a social network of TB transmission. Molecular genotyping was used to confirm SNA-detected clusters of TB.
RESULTS:TB patients not linked through conventional contact-investigation data were connected through mutual contacts or places of social aggregation, using SNA methods. In some instances, SNA detected connected groups prior to the availability of genotyping results. A positive correlation between positive results of contacts' tuberculin skin test (TST) and location in denser portions of the person-place network was observed (P<.01).
CONCLUSIONS:Correlation between TST-positive status and dense subgroup occurrence supports the value of collecting place data to help prioritize TB contact investigations. TB controllers should consider developing social network analysis capacity to facilitate the systematic collection, analysis, and interpretation of contact-investigation data.
The Journal of Infectious Diseases 11/2007; 196(10):1517-1527. · 6.41 Impact Factor
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ABSTRACT: To compare 15 completed network studies of STD/HIV transmission with regard to their structural characteristics. To determine similarities and differences in the network characteristics in different epidemiologic settings.
Combined analysis of nearly 40,000 dyads, using epidemiologic and network analytic methods.
In general, transmitting networks have a right-skewed degree distribution, a large single component, and small world characteristics. They vary with regard to concurrency, assortativity, and transitivity.
The analysis suggests that networks in which transmission takes place have a common network infrastructure, but that the actual level of transmission may be determined by factors specific to a study population. Specific quantitation of the relationship between transmission and network characteristics will require an amalgam of empirical and theoretical methods.
Sex Transm Dis 09/2007; 34(8):604-12. · 2.87 Impact Factor
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ABSTRACT: To examine the epidemiology of multiple infections in teenagers and their contacts.
To demonstrate a network approach to the prevalence of STDs/HIV.
A community-based network study of ethnographically representative adolescents.
Of the 512 interviewees, 90% of the boys and 80% of the girls were sexually active with many partners and exhibited age-assortative mixing. Prevalences of gonorrhea, chlamydia, and HSV-2 were high, but syphilis, Hepatitis C and HIV were virtually absent. The prevalence faced by subgroups differed from overall prevalence.
The presence of bacterial STDs and the absence of HIV, HCV, and syphilis may be the result of no IDU and assortative age mixing. Testing for multiple conditions, network assessment of prevalence, and inclusion of social contacts enhance understanding of STD epidemiology.
Sex Transm Dis 09/2007; 34(8):525-31. · 2.87 Impact Factor
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ABSTRACT: An investigation was conducted to determine factors associated with a syphilis outbreak in a rural North Carolina county.
A retrospective chart review was performed on 61 primary (PS), secondary (SS), and early latent (ELS) syphilis case patients reported in Columbus County between January 2001 and February 2002. Sociosexual network analysis was conducted using electronic contact tracing information.
We identified 20 PS, 25 SS, and 16 ELS case patients who were predominantly black. Seventy-two percent had reported >or=1 sexual partner with early syphilis, 51% used crack cocaine and/or had sex with a crack-using partner, and 31% exchanged sex for drugs or money. The sexual network exhibited predominantly linear connections between case patients and sexual partners. Adding social connections to the network further demonstrated dense cyclic interactions characteristic of core groups.
The syphilis outbreak in this rural community was associated with crack cocaine and exchange of sex for drugs in a densely interconnected sociosexual network.
Sex Transm Dis 05/2007; 34(5):280-7. · 2.87 Impact Factor
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ABSTRACT: The objective of this study was to describe the epidemiology of early syphilis among men in Connecticut, a moderate-prevalence region, in 2004.
The authors conducted a cross-sectional analysis of health department data.
Fifty-five cases were reported from 25 different towns. A majority of cases (82%) were reported among men who have sex with men, and 22% reported coinfection with HIV. Spatial analysis indicated moderate clustering of cases. Approximately half of 197 reported sex partners were not from Connecticut, including 28% from New York City and 20% from other states/countries. The median distance between partners was 48 km (30 miles). Twenty-three percent of syphilis cases had both local and nonlocal partners.
The current epidemiology of early syphilis in Connecticut is consistent with national trends. However, the dispersal of cases throughout the state and the high proportion of reported sex partners residing outside of Connecticut suggest that this state is not a core area of endemic transmission.
Sex Transm Dis 04/2007; 34(3):183-7. · 2.87 Impact Factor
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Journal of Adolescent Health 04/2007; 40(3):290-1; author reply 291-3. · 3.33 Impact Factor
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Sex Transm Dis 02/2007; 34(1):54-6; author reply 57-8. · 2.87 Impact Factor
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ABSTRACT: Prostitute women have the highest homicide victimization rate of any set of women ever studied. We analyzed nine diverse homicide data sets to examine the extent, trends, and perpetrators of prostitution-related homicide in the United States. Most data sources substantially under-ascertained prostitute homicides. As estimated from a conservative capture-recapture analysis, 2.7% of female homicide victims in the United States between 1982 and 2000 were prostitutes. Frequencies of recorded prostitute and client homicides increased substantially in the late 1980s and early 1990s; nearly all of the few observed pimp homicides occurred before the late 1980s. These trends may be linked to the rise of crack cocaine use. Prostitutes were killed primarily by clients, clients were killed mainly by prostitutes, and pimps were killed predominantly by pimps. Another conservative estimate suggests that serial killers accounted for 35% of prostitute homicides. Proactive surveillance of, and evidence collection from, clients and prostitutes might enhance the investigation of prostitution-related homicide.
Journal of Forensic Sciences 10/2006; 51(5):1101-8. · 1.23 Impact Factor
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ABSTRACT: Hepatitis C virus (HCV) is hyperendemic in drug injectors, yet social structural and behavioral factors underlying transmission are not well established.
We conducted a case-control study of HCV seroconversion in drug injectors, focusing on transmission within networks. Incident case subjects (n=17) and seronegative control subjects (n=42) reported injection and sex partners and referred as many as 5 for interviewing and blood testing. We performed nucleotide sequencing of HCV isolates from infected individuals.
Seventy-eight percent of recent injection partnerships involved behavior that could transmit HCV. Case subjects and control subjects were similar demographically and behaviorally. Case subjects, however, had more HCV-infected partners and consequently engaged in injection risk behavior with more infected partners. The injection network was mostly connected, dense, and cyclic, but the sexual network was highly fragmented. Although participants generally injected with partners of similar age, most HCV-uninfected participants recently had injected with infected partners. In at least 1 of 4 pairs of genetically linked infections, transmission appeared to be due to sharing of injection equipment other than syringes. Except for transmission pairs, network distance between incident case subjects and genetic distance between their HCV variants were uncorrelated.
Without dramatic reductions in injection risk behaviors, shattering of cohesive injection networks, and/or broad coverage of an effective vaccine, HCV will likely remain hyperendemic in drug injectors.
The Journal of Infectious Diseases 10/2006; 194(6):764-72. · 6.41 Impact Factor
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ABSTRACT: Little is known regarding whether partner characteristics explain sex differences in sexually transmitted infection (STI) rates in nonclinic-based, school-aged African American youth.
A random digit dial household sample of 14- to 19-year-old youth in San Francisco reported the total number, age, race, and perceived history of incarceration, gang membership, and level of sexual activity of their partners. Youth were tested for gonorrhea and chlamydia.
Female participants were more likely than male participants to have a partner who was older or had been incarcerated and less likely to have a non-African American partner. Controlling for partner number, female's odds ratio (OR) for having an STI was 1.39 (95% confidence interval [CI] = 0.98-1.98; P = 0.07). Controlling for partner incarceration and number of partners, the borderline sex difference was eliminated (OR = 1.07; 95% CI = 0.70-1.63).
Sex differences in STI rates among African American adolescents may be determined more by the risk of the partner than the risk of the individual.
Sex Transm Dis 09/2006; 33(8):480-4. · 2.87 Impact Factor
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ABSTRACT: To describe the reliability of reported dates of first and last sexual exposure, as elicited from sexually transmitted disease/human immunodeficiency virus cases during routine contact investigation, and determine their adequacy for assessing concurrency.
We used contact tracing data from 5 studies in which both members of 774 dyads were interviewed and named each other as sex partners. We assessed partners' agreement on the dates of first and last exposure as related to precision (to the day, month, or year) of reported dates and demographic and behavioral characteristics of the dyad. We performed simulations that introduced reporting error, based on our observed data, to posited "true" temporal configurations of partnerships to assess the impact of unreliability in reporting on the measurement of concurrency.
Thirty-two percent of dyads agreed on the exact date of first sexual exposure, and 36% did so for the date of last sexual exposure. Sixty-four percent agreed within 30 days on the date of first sexual exposure, and 81% did so for the date of last sexual exposure. The reliability of reported dates was positively related to the precision of the reports. Agreement on reported exposure dates was not meaningfully associated with any of the sociodemographic and behavioral variables available. Based on simulations, the positive predictive value of reported dates for estimating concurrency is approximately 80% over a wide range of conditions.
These data suggest that the reliability of reported exposure dates is reasonably good but that estimating concurrency with reported dates is subject to some error. Data designed for the purpose and analyzed with adequate attention to the statistical and epidemiologic issues of assessing concurrency are needed.
Sex Transm Dis 06/2006; 33(5):277-83. · 2.87 Impact Factor
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PLoS Medicine 02/2006; 3(1):e64; author reply e67. · 16.27 Impact Factor
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ABSTRACT: Prior research suggests that arrest, compared with no police detection, of some types of offenders does not decrease the chances they will reoffend.
We assessed the specific deterrent effect of arrest for patronizing a street prostitute in Colorado Springs by comparing the incidence of arrest for clients of prostitutes first detected through public health surveillance with the incidence of rearrest for clients first detected by police arrest. Although these sets of clients were demographically and behaviorally similar, arrest reduced the likelihood of a subsequent arrest by approximately 70%. In other areas of the United States, arrest did not appear to displace a client's patronizing.
Our results suggest that apprehending clients decreases their patronizing behavior substantially.
PLoS ONE 02/2006; 1:e60. · 4.09 Impact Factor
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ABSTRACT: The objective of this study was to examine the relationship between social distance (measured as the geodesic, or shortest distance, between 2 people in a connected network) and geographic distance (measured as the actual distance between them in kilometers [km]).
We used data from a study of 595 persons at risk for HIV and their sexual and drug-using partners (total N = 8920 unique individuals) conducted in Colorado Springs, Colorado, from 1988 to 1992--a longitudinal cohort study that ascertained sociodemographic, clinical, behavioral, and network information about participants. We used place of residence as the geographic marker and calculated distance between people grouped by various characteristics of interest.
Fifty-two percent of all dyads were separated by a distance of 4 km or less. The closest pairs were persons who both shared needles and had sexual contact (mean = 3.2 km), and HIV-positive persons and their contacts (mean = 2.9). The most distant pairs were prostitutes and their paying partners (mean = 6.1 km). In a connected subset of 348 respondents, almost half the persons were between 3 and 6 steps from each other in the social network and were separated by a distance of 2 to 8 km. Using block group centroids, the mean distance between all persons in Colorado Springs was 12.4 km compared with a mean distance of 5.4 km between all dyads in this study (P <0.0001). The subgroup of HIV-positive people and their contacts was drawn in real space on a map of Colorado Springs and revealed tight clustering of this group in the downtown area.
The association of social and geographic distance in an urban group of people at risk for HIV provides demonstration of the importance of geographic clustering in the potential transmission of HIV. The proximity of persons connected within a network, but not necessarily known to each other, suggests that a high probability of partner selection from within the group may be an important factor in maintenance of HIV endemicity.
Sex Transm Dis 08/2005; 32(8):506-12. · 2.87 Impact Factor
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ABSTRACT: To determine whether African American adolescents, whose recent sex partners reported having another sex partner, are at increased risk for exposure to genital chlamydial infection or gonorrhea.
A household sample of low-income urban African American adolescents 14 to 19 years of age, up to two of their close friends, and their sex partners were interviewed and tested for gonorrhea and chlamydial infection.
Thirty-four of 145 adolescents had at least one recent sex partner infected with Neisseria gonorrhoeae and/or Chlamydia trachomatis. The adjusted model showed that adolescents, whose recent sex partners reported having another sex partner, were more likely to have a recent sex partner with gonorrhea and/or chlamydial infection.
In addition to individual factors, network factors may explain why African American adolescents are at increased risk for exposure to sexually transmitted infections (STIs). Multi-level community-based interventions may need to address network factors along with personal behaviors in order to prevent STIs among low-income urban African American adolescents.
Journal of Pediatrics 05/2005; 146(4):518-22. · 4.11 Impact Factor
