Contact tracing: comparing the approaches for sexually transmitted diseases and tuberculosis.

SETTING: Literature review for the process of contact tracing for sexually transmitted diseases (STD) and for tuberculosis (TB), focusing on articles that report results of studies or commentary. OBJECTIVE: To compare and contrast contact tracing in order to highlight emerging commonalities. DESIGN: A descriptive review, based on Medline search with augmentation from other published and unpublished sources. RESULTS: Contact tracing for STD and TB have some obvious differences because of differing routes of transmission, differing sensibilities required to work with the affected populations, a different potential for anonymous contacts, and a major difference in the epidemiologic value of biomarkers. Nonetheless, the convergence of these processes on disadvantaged populations where drug use and sexual activity are important social factors has engendered an increasing similarity. CONCLUSION: A broadened approach to both, with greater attention to how ancillary contacts and associates may be of use in interrupting deeply embedded endemic disease transmission, deserves further study. Some newer approaches in the use of network-informed methods to elicit contacts and investigate the community dynamics of transmission may be of particular value in TB case investigation. These strategies will be enhanced by the availability of DNA fingerprinting, a powerful biomarker of recent Mycobacterium tuberculosis transmission and case association (a technology not available for STD contact tracing).

A network-informed approach to investigating a tuberculosis outbreak: implications for enhancing contact investigations.

BACKGROUND: To elucidate networks of Mycobacterium tuberculosis transmission, it may be appropriate to characterize the types of relationships among tuberculosis (TB) cases and their contacts (with and without latent TB infection) in addition to relying on traditional efforts to distinguish 'close' from 'casual' contacts. SETTING: A TB outbreak in a US low incidence state. OBJECTIVE: To evaluate whether social network analysis can provide insights into transmission settings that might otherwise go unrecognized by routine practices. DESIGN: All adult outbreak-associated cases (n = 19) and a convenience sample of their contacts with and without latent TB infection (LTBI) (n = 26) were re-interviewed in 2001 using a structured questionnaire. Network analysis software was used to create diagrams illustrating important persons within the outbreak network, as well as types of activities TB cases engaged in with their contacts. RESULTS: Drug use and drug sharing were more commonly reported among cases and their infected contacts than among contacts without LTBI. TB cases central to the outbreak network used crack cocaine, uncovering the need to focus control efforts on specific sites and persons involved in illicit drug use. CONCLUSION: Outbreaks occur even in areas with low TB incidence, frequently among groups whose drug use or other illegal activities complicate control efforts. TB programs should consider the use of network analysis as a supplement to routine contact investigations to identify unrecognized patterns of M. tuberculosis transmission.

Risk network structure in the early epidemic phase of HIV transmission in Colorado Springs.

This study describes the risk network structure of persons with HIV infection during its early epidemic phase in Colorado Springs, USA, using analysis of community-wide HIV/AIDS contact tracing records (sexual and injecting drug partners) from 1985 to 1999. Paired partner information from other STD/HIV programme records was used to augment network connections. Analyses were conducted with and without this supplemental information. The results suggest that a combined dendritic and cyclic structural network pattern is associated with low to moderate HIV propagation in Colorado Springs, and may account for the absence of intense propagation of the virus.

Sexual network structure as an indicator of epidemic phase.

Ascertaining epidemic phase for a sexually transmitted disease (STD) has depended on secular trend data which often contain significant artefacts. The usefulness of sexual network structure as an indicator of STD epidemic phase is explored in an analysis of community wide genital chlamydia reports, with network analysis of interviewed cases and linked sexual partners, in Colorado Springs, USA, 1996 to 1999. In this period, the chlamydia case rate per 100,000 increased by 46%. Three quarters of cases (n=4953) were interviewed, nominating 7365 partners; these, combined with index cases, made up the 9114 persons in the network. Epidemiologic analysis of cases suggests that secular trend increases are artefactual. Network analysis supports this view: overall network structure is fragmented and dendritic, notably lacking the cyclic (closed loops) structures associated with network cohesion and thus with efficient STD transmission. Comparison of network structure with that of an intense STD outbreak (characterised by numerous cyclic structures) suggests low level or declining endemic rather than epidemic chlamydia transmission during the study interval. These observations accord with intuitive and stochastic predictions.

The Atlanta Urban Networks Study: a blueprint for endemic transmission.

OBJECTIVE: To study prospectively social networks and behavior in a group of persons at risk for HIV because of their drug-using and sexual practices, with particular emphasis on the interaction of risks and concomitant network structure. METHODS: A longitudinal study was conducted of 228 respondents in Atlanta, Georgia in six inner-city community chains of connected persons, interviewing primary respondents and a sample of their contacts every 6 months for 2 years. Ascertained were: HIV and immunologic status; demographic, medical, and behavioral factors; and the composition of the social, sexual, and drug-using networks. RESULTS: The prevalence of HIV in this group was 13.3% and the incidence density was 1.8% per year. Substantial simultaneity of risk-taking was observed, with a high level of both non-injecting (crack, 82%) and injecting (heroin, cocaine or both, 16 30%) drug use, the exchange of sex or money for drugs by men (approximately 35%) and women (57-71%), and high frequency of same-sex sexual activity by men (9.4%) and women (33%). The intensity of interaction, as measured by network features such as microstructures and concurrency, was significantly greater than that observed in a low prevalence area with little endemic transmission. CONCLUSION: The traditional hierarchical classification of risk for HIV may impede our understanding of transmission dynamics, which, in the setting of an inner-city population, is characterized by simultaneity of risk-taking, and moderately intense network interactions. The study provides further evidence for the relationship of network structure to transmission dynamics, but highlights the difficulties of using network information for prediction of individual seroconversion.

Birds of a feather: using a rotational box plot to assess ascertainment bias.

BACKGROUND: Comparability of study participants with non-participants is customarily assessed by contrasting the distributions of sociodemographic characteristics. Such comparisons do not necessarily provide insight into whether or not participants of a given subgroup are similar to non-participants of the same subgroup. A geographical information system (GIS) may provide such insight by visually displaying the spatial distributions of participants and non-participants. In a previously reported study of heterosexuals at elevated risk for human immunodeficiency virus (HIV), traditional methods suggested distributional differences in the demographic characteristics of participants and non-participants. METHODS: Based on residential address co-ordinates for each subgroup member, we used the subgroup's centroid as the origin and constructed a 360 degrees series of overlapping box plots of the distance of subgroups members to the origin, thereby producing closed polygons for each of the box plot demarcators. RESULTS: These rotational box plots revealed similar geographical distributions for most participant and non-participant subgroups, with the exception of African-American men and women. CONCLUSIONS: Observed differences resulted in part from the study design, and provided some insight into sampling problems encountered in social network studies. Based on Tobler's supposition that 'nearby things tend to be alike', the rotational box plot is a useful additional tool for investigating sample bias.

The effect of treating sexually transmitted diseases on the transmission of HIV in dually infected persons: a clinic-based estimate. Ad Hoc STD/HIV Transmission Group.

BACKGROUND: The effect of sexually transmitted disease (STD) treatment on HIV transmission is a topic of considerable current interest and controversy. GOAL: To assess the potential effect of STD treatment on HIV transmission in persons who are dually infected with STD and HIV. STUDY DESIGN: Using data from eight STD clinic sites in the United States, the authors estimate the actual achievable reduction in HIV transmission by multiplying the prevented fraction associated with treatment of STDs (set at an average of 0.8) by the maximum potential reduction in HIV transmission achieved by treating STDs (using an average relative risk of 3.0 for increased HIV transmission in the presence of STDs). Subgroup analysis assessed infection proportions for genital ulcer disease, nonulcerative STDs, and any STD by sex, ethnicity, age, and sexual orientation. RESULTS: The maximum achievable reduction in HIV transmission from dually infected persons to their partners is approximately 33%. The actual achievable reduction is approximately 27% (range, 10.0-38.1%) at the eight clinic sites. If each of the 4,516 dually infected persons in this cohort experienced a single sexual exposure with an uninfected person, 28 HIV infections would occur in the absence of STD treatment whereas 16 infections would occur with STD treatment. CONCLUSIONS: The estimate of a 27% reduction provides a qualitative assessment of the potential impact of STD treatment on HIV transmission in the absence of any other behavioral intervention. Identification of dually infected persons in STD clinics is an important mechanism for targeting interventions to a social milieu with high risk for HIV infection and other STDs.

Chlamydia transmission: concurrency, reproduction number, and the epidemic trajectory.

To identify factors that influence individual and group transmission of Chlamydia, the authors conducted community-wide contact tracing of chlamydia cases in Colorado Springs, Colorado, from mid-1996 to mid-1997. Case patients identified persons with whom they had had contact during the 6 months preceding diagnosis; contacts were actively sought and offered DNA amplification testing. Sexual contact networks were used to identify "source cases" and "spread cases," permitting estimation of the basic reproduction number (R0) for individuals and groups. Network and epidemiologic factors influencing R0 were assessed using univariate and multivariate procedures. Of 1,309 case patients, 1,131 (86%) were interviewed, and 2,409 contacts were identified. The 1,131 interviewed cases yielded 623.9 computed spread cases, for an overall R0 of 0.55. Few subgroups analyzed yielded a mean R0 exceeding unity-an observation in keeping with routine surveillance information which suggests that chlamydia incidence is declining in Colorado Springs. Concurrency, a network measure of simultaneous partnerships, was the most powerful predictor of transmission. Direct estimation of basic reproduction numbers for chlamydia using contact tracing techniques is feasible and can produce useful data with which to prioritize control efforts, evaluate interventions, and gauge the place of chlamydia on the epidemic continuum.

Invoking, monitoring, and relinquishing a public health power: the health hold order.

OBJECTIVE: To describe a quarter-century's use of a public health power (Health Hold Orders) as an adjunct to noncoercive sexually transmitted disease (STD) control efforts in a middle-American city. METHODS: Persons arrested for prostitution were involuntarily detained for up to 72 hours if they had not been tested for STD within 30 days of arrest. Such persons were mandatorily tested/treated for STD and voluntarily tested for HIV by health department providers in Colorado Springs from mid-1970 through 1994. RESULTS: Prostitutes viewed temporary detention as inconvenient, but not as inappropriate. Over the 25-year interval, 4,965 examinations in prostitutes yielded 818 positive gonorrhea tests; the 1,564 tests performed under the health-hold order yielded 218 positive results. Positivity rates among prostitutes locally for reportable STD/HIV declined substantially during the period of observation, providing support for termination of the involuntary detention system. CONCLUSIONS: The involuntary detention system contributed to observed communitywide declines in STD/HIV prevalence. Our experience demonstrates the importance of surveillance and empiric validation in public health practice.

Network structural dynamics and infectious disease propagation.

We aimed to relate dynamic changes in risk-network (sex and/or injecting drug) structure to observe STD/HIV transmission. We analysed macro- and micro-structural elements in 2 heterosexual networks, augmented by ethnographic observations. In a Colorado cohort of injecting drug users (n = 595), measures of subgroup formation and of density of activity show decrease of network cohesion over time; only one HIV transmission was observed in 3 years. In a group of adolescent heterosexuals in Georgia (n = 99), the reverse process (increase in structural cohesion) was associated with efficient syphilis transmission: 10 cases were observed. Changes in personal risk behaviours over time were modest. STD/HIV transmission patterns were associated with intensification or diminution of network cohesion. Network and ethnographic data suggest that enhanced connectivity facilitates transmission while segmentation impedes it, suggesting opportunities for interventions. These data also emphasize the need to re-evaluate purely behavioural explanations of STD/HIV transmission.

Social network dynamics and HIV transmission.

OBJECTIVE: To prospectively study changes in the social networks of persons at presumably high risk for HIV in a community with low prevalence and little endogenous transmission. METHODS: From a cohort of 595 persons at high risk (prostitutes, injecting drug users, and sexual partners of these persons) and nearly 6000 identified contacts, we examined the social networks of a subset of 96 persons who were interviewed once per year for 3 years. We assessed their network configuration, network stability, and changes in risk configuration and risk behavior using epidemiologic and social network analysis, and visualization techniques. RESULTS: Some significant decrease in personal risk-taking was documented during the course of the study, particularly with regard to needle-sharing. The size and number of connected components (groups that are completely connected) declined. Microstructures (small subgroups of persons that interact intensely) were either not present, or declined appreciably during the period of observation. CONCLUSIONS: In this area of low prevalence, the lack of endogenous transmission of HIV may be related in part to the lack of a network structure that fosters active propagation, despite the continued presence of risky behaviors. Although the relative contribution of network structure and personal behavior cannot be ascertained from these data, the study suggests an important role for network configuration in the transmission dynamics of HIV.

Using social network and ethnographic tools to evaluate syphilis transmission.

BACKGROUND AND OBJECTIVES: Partner notification has been the cornerstone for the prevention and control of syphilis in the United States. This technique may not make full use of contextual data that an ethnographic and social network approach can offer. GOALS OF THE STUDY: The occasion of a syphilis outbreak among young people was used to investigate the applicability of a social network approach and to test the validity of several traditional approaches to syphilis epidemiology. STUDY DESIGN: An outbreak of syphilis was investigated by interviewing both infected and noninfected people, by directing resources based on network association, by creating and evaluating network diagrams as an aid to the epidemiologic process, and by including ethnographic observations as part of outbreak management. RESULTS: Diagrammatic display of network growth provided a useful alternative to the traditional epidemic curve. Case prevention was demonstrated by identifying uninfected people with multiple concurrent exposures. Concurrent, overlapping exposure in infected people rendered traditional "source" and "spread" criteria moot. CONCLUSIONS: The current discussions of partner notification may be informed by recognizing that it is a subset of a broader and potentially more powerful approach. This approach calls some basic tenets of syphilis epidemiology into question.

Sociometric risk networks and risk for HIV infection.

OBJECTIVES: This study examined whether networks of drug-injecting and sexual relationships among drug injectors are associated with individual human immunodeficiency virus (HIV) serostatus and with behavioral likelihood of future infection. METHODS: A cross-sectional survey of 767 drug injectors in New York City was performed with chain-referral and linking procedures to measure large-scale (sociometric) risk networks. Graph-theoretic algebraic techniques were used to detect 92 connected components (drug injectors linked to each other directly or through others) and a 105-member 2-core within a large connected component of 230 members. RESULTS: Drug injectors in the 2-core of the large component were more likely than others to be infected with HIV. Seronegative 2-core members engaged in a wide range of high-risk behaviors, including engaging in risk behaviors with infected drug injectors. CONCLUSIONS: Sociometric risk networks seem to be pathways along which HIV travels in drug-injecting peer groups. The cores of large components can be centers of high-risk behaviors and can become pockets of HIV infection. Preventing HIV from reaching the cores of large components may be crucial in preventing widespread HIV epidemics.

Personal risk taking and the spread of disease: beyond core groups.

Disease control efforts directed at human immunodeficiency virus are predicated on the need to reduce personal risk behaviors; that approach may not adequately reflect the complicated interplay between personal behaviors and the social setting in which they occur. Efforts to date, including the application of population ecology, the development of the core group hypothesis, and the use of compartment models to describe disease transmission, have aided in understanding the dynamics of transmission and have highlighted the relationship between personal risk taking and population risk. An area for further development is the application of the techniques of social network analysis to infectious disease spread. Initial work suggests that social structure may act as a barrier (or facilitator) in disease transmission and that the epidemiologic impact of a risky act varies with the social setting. The local context for risk behaviors has important implications for the dynamics of transmission.

Delivering breast and cervical cancer screening services to underserved women: Part II. Implications for policy.

Many breast and cervical cancer screening (BCCS) programs for underserved women employ strategies to increase the use of preventive services. In Phase I of a two-phase study, strategies were identified and assessed. In Phase II, we further assess strategies previously identified and comment on policy implications. Site visits were conducted at BCCS programs that had used one successful strategy identified during Phase I, provided services to underserved women, and were located in different geographic regions. The federally funded National Breast and Cervical Cancer Early Detection Programs (NBCCEDP) were also considered for site visits. Interviews were completed and available data were reviewed. A descriptive and qualitative analysis was completed. Programs visited were found to be increasing the use of BCCS services for the defined target populations. Some programs focused on outreach and recruitment. Other programs focused on clinical preventive services with little emphasis on outreach and recruitment. Management information systems were used by most programs. We found that there continues to be a large number of women not receiving BCCS services. Some programs have had to limit outreach and recruitment because the clinical preventive services offered are at capacity. Programs need to have a balanced approach to providing services from the outset. Existing programs may need to establish partnerships to provide comprehensive BCCS services to underserved women. Because the unmet need (women who have not received BCCS services) exceeds available clinical preventive services, it is a challenge to know how to best use available resources.

Delivering breast and cervical cancer screening services to underserved women: Part I. Literature review and telephone survey.

Although breast and cervical cancer screening procedures have been shown to reduce morbidity and mortality, many women are not using these services. These women are likely to be older, of ethnic or racial minority, of low socioeconomic status, less educated, underinsured, or living in rural locations. Many breast and cervical cancer screening programs employ strategies to increase use. In order to identify and assess those strategies, we reviewed the literature and completed a telephone survey, altogether assessing 61 programs. Our study identified several strategies and found that not all strategies work for all women. Management systems directed to both patients and providers consistently are effective for most underserved women. Community-based outreach and integration of preventive services at the primary health care (PHC) site are effective strategies for both African American and Hispanic women. Use of mass media has been successful when targeted toward Hispanic women, but not when targeted toward African American women. Mobile units and integration of preventive services at PHC sites are effective strategies for elderly women. In many cases, a combination of strategies may be effective. Programs should employ strategies best suited to their target populations.

Syphilis control. The historic context and epidemiologic basis for interrupting sexual transmission of Treponema pallidum.

Syphilis control has been the prototypic sexually transmitted disease (STD) public health program of the 20th century. However, the disease remains nearly as much an epidemiologic enigma as it did in the early 1900s. This article examines the historic and epidemiologic bases for syphilis control, using unpublished data to supplement a recent model of STD transmission. The authors recommend building on such traditional individually oriented strategies as case finding, partner notification, and presumptive treatment as a basis for future community-oriented, population-based strategies including (but not limited to) selective mass treatment in high-prevalence populations. Using epidemiologic information to target population-level interventions will be the paradigm for syphilis control in the 20th century.