AIDS epidemiology in Africa: a changing of the guard.

With recent implementation of studies specifically designed to empirically assess the contribution of both sexual and blood-borne exposures to local HIV transmission in sub-Saharan Africa, and with the arrival of a new generation of investigators, a picture of HIV transmission routes of improved validity is emerging. Seven years ago the International Journal of STD & AIDS (IJSA) began actively encouraging reexamination of the prevailing view that penile-vaginal sex was driving African HIV epidemics, welcoming debate via manuscript submission and presentation of fresh scientific evidence. Although the IJSA-published dissenting views have largely been ignored, dismissed or fiercely resisted by established HIV researchers and allied health agencies, new approaches may yet elicit more rational, evidence-based responses. Several such contributions appear in IJSA's present theme issue on aspects of HIV epidemiology in Africa. The focus on recent empiric data, rather than on modelling or speculation, no longer leaves reasonable doubt that sexual behaviours are insufficient to explain 'Why Africa?' It is fitting that this progress was encouraged, from beginning to end, by long-time, and now departing IJSA Editor-in-Chief, Dr Wallace Dinsmore.

Diverse blood exposures associated with incident HIV infection in Calabar, Nigeria.

Few types of blood exposures have been assessed in relation to incident HIV infection in sub-Saharan Africa, despite evidence that penile-vaginal sex cannot account for the epidemic in the region. To investigate correlates of incident HIV infection in Calabar, Nigeria, we surveyed clients at voluntary HIV counselling and testing centres. Participating clients who tested multiple times were generally similar to those testing only once in terms of demographic characteristics, sexual and blood exposures and HIV prevalence. Blood exposures were common. Serial testers had a 10% annual incidence of HIV infection. Seroconverters and seronegative serial testers were similar on most demographic characteristics and sexual exposures. However, seroconverters were more likely than seronegatives to report blood exposures during the test interval, both for most specific exposures as well as summary measures of blood exposures. In particular, seroconverters were substantially more likely to report one of a set of blood exposures that cannot be explained as a consequence of unprotected vaginal sex or of health care for symptoms of HIV infection (adjusted odds ratio = 6.6, 95% confidence interval = 1.2-38). The study design we used is an inexpensive approach for describing the local epidemiology of HIV transmission and can also serve as the foundation for more definitive investigations that employ contact tracing and sequencing of HIV DNA.

Horizontally-acquired HIV infection in Kenyan and Swazi children.

Despite many reports of HIV-infected African children who have HIV-uninfected mothers, little is known about the extent and modes of horizontal HIV transmission in African children. We estimated the extent of horizontal HIV transmission in Swazi children by comparing child and mother HIV statuses in the 2006-2007 Swaziland Demographic and Health Survey (DHS). To identify correlates of horizontal HIV transmission, we conducted a case-control study of Kenyan children with horizontally acquired HIV infections and their uninfected siblings. Of 50 HIV-positive Swazi children in the DHS, 11 (weighted percent = 20, 95% confidence interval 11-33%) had HIV-negative mothers. These 11 children represented 0.6% of all Swazi children aged 2-12 who lived with their mothers. In the Kenyan study, children with horizontally acquired HIV infections had more kinds of blood exposures than their uninfected siblings. In particular, punctures related to health care for suspected malaria (phlebotomy, injection and infusion), injections while hospitalized and dental surgery (especially by informal providers) were more common in infected children. Horizontal HIV transmission appears to be common in some sub-Saharan African countries, and blood exposures seem to be the most likely routes of transmission. Rigorous surveillance and investigation of horizontally acquired HIV infection in children are urgently needed, along with universal public education about risks of specific blood exposures and ways to avoid them.

How to contain generalized HIV epidemics? A plea for better evidence to displace speculation.

In the worst generalized HIV epidemics in East and Southern Africa, from one-quarter to three-quarters of women aged 15 years can expect to be living with HIV or to have died with AIDS by age 40 years. This disaster continues in the face of massive HIV prevention programmes based on current inexact knowledge of HIV transmission pathways and risks. To stop this disaster, both the public and public health experts need better information about the specific factors that allow HIV to propagate so extensively in countries with generalized epidemics. This knowledge could be acquired by tracing HIV infections to their source - especially tracing HIV infections in women of all ages, and tracing unexplained HIV infections in children with HIV-negative mothers.

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.

Sexual networks and sexually transmitted infections: a tale of two cities.

Research on risk behaviors for sexually transmitted infections (STIs) has revealed that they seldom correspond with actual risk of infection. Core groups of people with high-risk behavior who form networks of people linked by sexual contact are essential for STI transmission, but have been overlooked in epidemiological studies. Social network analysis, a subdiscipline of sociology, provides both the methods and analytical techniques to describe and illustrate the effects of sexual networks on STI transmission. Sexual networks of people from Colorado Springs, Colorado, and from Winnipeg, Manitoba, Canada, infected with chlamydia during a 6-month period were compared. In Winnipeg, 442 networks were identified, comprising 571 cases and 663 contacts, ranging in size from 2 to 20 individuals; Colorado Springs data yielded 401 networks, comprising 468 cases and 700 contacts, ranging in size from 2 to 12 individuals. Taking differing partner notification methods and the slightly smaller population size in Colorado Springs into account, the networks from both places were similar in both size and structure. These smaller, sparsely linked networks, peripheral to the core, may form the mechanism by which chlamydia can remain endemic, in contrast with larger, more densely connected networks, closer to the core, which are associated with steep rises in incidence.

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.

Prostitution and the sex discrepancy in reported number of sexual partners.

One of the most reliable and perplexing findings from surveys of sexual behavior is that men report substantially more sexual partners than women do. We use data from national sex surveys and studies of prostitutes and their clients in the United States to examine sampling bias as an explanation for this disparity. We find that prostitute women are underrepresented in the national surveys. Once their undersampling and very high numbers of sexual partners are factored in, the discrepancy disappears. Prostitution's role in the discrepancy is not readily apparent because men are reluctant to acknowledge that their reported partners include prostitutes.

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.