Peak HIV prevalence: a useful outcome variable for ecological studies

Prevalence of macrolide resistance in Treponema pallidum is associated with macrolide consumption

We hypothesized that the large global variations in the prevalence of macrolide resistance in Treponema pallidum are related to differences in population-level macrolide consumption. The hypothesis was tested by, at a country-level, regressing the peak prevalence of macrolide resistance against the national macrolide consumption in the year prior to this, controlling for the year of the resistance prevalence estimate. A strong association was found between the per capita consumption of macrolides and macrolide resistance (coefficient 0.7, 95 % confidence interval 0.2-0.12, P=0.009).

It's the network, stupid: a population's sexual network connectivity determines its STI prevalence

There is little consensus as to why sexually transmitted infections (STIs), including HIV and bacterial vaginosis (BV) are more prevalent in some populations than others. Using a broad definition of sexual network connectivity that includes both structural and conductivity-related factors, we argue that the available evidence suggests that high prevalence of traditional STIs, HIV and BV can be parsimoniously explained by these populations having more connected sexual networks. Positive feedback, whereby BV and various STIs enhance the spread of other STIs, then further accentuates the spread of BV, HIV and other STIs. We review evidence that support this hypothesis and end by suggesting study designs that could further evaluate the hypothesis, as well as implications of this hypothesis for the prevention and management of STIs.

It's the network, stupid: a population's sexual network connectivity determines its STI prevalence

There is little consensus as to why sexually transmitted infections (STIs), including HIV and bacterial vaginosis (BV) are more prevalent in some populations than others. Using a broad definition of sexual network connectivity that includes both structural and conductivity-related factors, we argue that the available evidence suggests that high prevalence of traditional STIs, HIV and BV can be parsimoniously explained by these populations having more connected sexual networks. Positive feedback, whereby BV and various STIs enhance the spread of other STIs, then further accentuates the spread of BV, HIV and other STIs. We review evidence that support this hypothesis and end by suggesting study designs that could further evaluate the hypothesis, as well as implications of this hypothesis for the prevention and management of STIs.

Strong associations between national prevalence of various STIs suggests sexual network connectivity is a common underpinning risk factor

Background

If national peak Human Immunodeficiency Virus (HIV) prevalence is positively associated with the prevalence of other sexually transmitted infections (STIs) from before or early on in the HIV epidemics this would suggest common underlying drivers.

Methods

Pearson’s correlations were calculated between the prevalence of seven STIs at a country-level: chlamydia, gonorrhoea, trichomoniasis, syphilis, bacterial vaginosis, herpes simplex virus-2 (HSV-2) and HIV.

Results

The prevalence of all the STIs was highest in the sub-Saharan African region excluding chlamydia. The prevalence of all seven STIs were positively correlated excluding chlamydia. The correlations were strongest for HIV-HSV-2 (r = 0.85, P < 0.0001) and HSV-2-trichomoniasis (r = 0.82, P < 0.0001).

Conclusion

Our results of a generally positive association between the prevalences of a range of STIs suggests that higher prevalences were driven by common underlying determinants. We review different types of evidence which suggest that differential sexual connectivity is a plausible common determinant.

Space-time migration patterns and risk of HIV acquisition in rural South Africa

Objective:

To quantify the space-time dimensions of human mobility in relationship to the risk of HIV acquisition.

Methods:

We used data from the population cohort located in a high HIV prevalence, rural population in KwaZulu-Natal, South Africa (2000–2014). We geolocated 8006 migration events (representing 1 028 782 km traveled) for 17 743 individuals (≥15 years of age) who were HIV negative at baseline and followed up these individuals for HIV acquisition (70 395 person-years). Based on the complete geolocated residential history of every individual in this cohort, we constructed two detailed time-varying migration indices. We then used interval-censored Cox proportional hazards models to quantify the relationship between the migration indices and the risk of HIV acquisition.

Results:

In total, 17.4% of participants migrated at least once outside the rural study community during the period of observation (median migration distance = 107.1 km, interquartile range 18.9–387.5). The two migration indices were highly predictive of hazard of HIV acquisition (P < 0.01) in both men and women. Holding other factors equal, the risk of acquiring HIV infection increased by 50% for migration distances of 40 km (men) and 109 km (women). HIV acquisition risk also increased by 50% when participants spent 44% (men) and 90% (women) of their respective time outside the rural study community.

Conclusion:

This in-depth analysis of a population cohort in a rural sub-Saharan African population has revealed a clear nonlinear relationship between distance migrated and HIV acquisition. Our findings show that even relatively short-distance migration events confer substantial additional risk of acquisition.

The Prevalence of Syphilis from the Early HIV Period is Correlated With Peak HIV Prevalence at a Country Level

BACKGROUND

Could we have predicted national peak HIV based on syphilis prevalence in the 1990s? Earlier studies have shown positive correlations between various sexually transmitted infections at different population levels. In this article, we test the hypothesis that there was a residual variation in the national prevalence rates of syphilis and that these rates could predict subsequent peak HIV prevalence rates.

METHODS

This analysis uses linear regression to evaluate the country-level relationship between antenatal syphilis prevalence (1990-1999) and peak HIV prevalence. Antenatal syphilis data were taken from an Institute for Health Metrics and Evaluation database on the prevalence of syphilis in low-risk populations. Peak HIV prevalence was calculated based on data taken from the Global Health Observatory Data Repository of the World Health Organization.

RESULTS

A moderately strong association is found for the 76 countries with data available (R = 0.53, P < 0.001). The association was weakened but remained significantly positive when we adjusted for the type of syphilis testing used.

CONCLUSIONS

Syphilis prevalence in the 1990s predicted approximately 53% of the variation in peak HIV prevalence. Populations with generalized HIV epidemics had a higher prevalence of syphilis in the pre-HIV period. This finding provides additional rationale to carefully monitor sexual behavior, sexual networks, and sexually transmitted infection incidence in these populations.

A population's higher-risk sexual behaviour is associated with its average sexual behaviour-An ecological analysis of subpopulations in Ethiopia, Kenya, South Africa, Uganda and the United States

BACKGROUND

Given the large variation in the prevalence of sexually transmitted infections between populations it is important to characterize how sexual vary between populations. In this paper we assess how the distribution of lifetime sexual partners varies between populations. We ask: do populations with higher mean lifetime sexual partners merely differ by virtue of the presence of a core-group with increased number of partners or do the population distributions move as more coherent wholes?

METHODS

We defined those in the top decile of lifetime sex partners in each country as constituting the higher-risk behaviour group (HRB). Spearman's correlation was used to evaluate the relationship between mean lifetime partners and prevalence of those in the HRB by ethnic group within Ethiopia, Kenya, South Africa, Uganda and the United States. In each case, data from nationally representative surveys were used. Two-sample Wilcoxon rank-sum were applied to test if there was a difference in the number of lifetime partners between the highest and lowest-risk subpopulations, separately for men and women. To account for autocorrelation, all analyses were conducted using means/medians excluding those in the HRB. A P-value of <0.05 was considered statistically significant.

RESULTS

In each country, a positive correlation existed between subpopulations' mean lifetime partners and the prevalence of the HRB. Spearman's correlation varied from 0.20 to 0.99 for men and 0.74 to 1.0 for women. This association was statistically significant in 6 out of 10 comparisons. There was a statistically significant difference in the number of lifetime partners between the highest and lowest-risk ethnic groups in all countries except South Africa, where the difference was only significant for women.

CONCLUSIONS

Our results suggest that sexual behaviours vary coherently between different populations. As such, sexually transmitted infection control efforts would benefit from including both targeted campaigns focusing on the HRB and population-strategies that seek to address factors responsible for high mean risk behaviour.

Conceptual framework and research methods for migration and HIV transmission dynamics

Migration and mobility have had a profound influence on the global HIV epidemic. We propose a network-dyadic conceptual model to interpret previous literature and inform the development of future research with respect to study design, measurement methods, and analytic approach. In this model, HIV transmission is driven by risk behaviors of migrants that emerges and is enabled by mobility, the bridging of sub-epidemics across space and time, and the displacement effects on the primary residential sending community for migrants. To investigate these causal pathways, empirical study designs must measure the relative timing of migratory events, sexual risk behaviors, and incident HIV infections. Network-based mathematical models using empirical data on partnerships help gain insight into the dynamic disease transmission systems. Although the network-dyadic conceptual model and related network methods may not address all questions related to migration and HIV, they provide a unified approach for future research on this important topic.

What underpins the decline in syphilis in Southern and Eastern Africa? An exploratory ecological analysis

BACKGROUND

AIDS mortality played an important role in the decline in syphilis prevalence in the USA, but its effect on the dramatic reduction in syphilis prevalence in Southern and Eastern Africa has not been explored. In this ecological study, we investigated the extent to which the relationship between syphilis and HIV prevalence at a population level varied between the early and late periods of the HIV epidemic.

METHODS

We performed linear regression analysis to measure the association between the national prevalence of syphilis and the peak-HIV prevalence in the early and late phases of the HIV epidemic in 11 countries of Southern and Eastern Africa.

RESULTS

Our analysis showed a strong positive association between peak-HIV prevalence and syphilis prevalence early in the HIV epidemic (R(2)=0.59; p=0.006). Although only of borderline statistical significance, this linear relationship between HIV prevalence and syphilis prevalence switched to a negative direction late in the HIV epidemic (R(2)=0.32; p=0.07).

CONCLUSIONS

AIDS mortality may have played an important role in the decline in syphilis in this region. Consequently, with AIDS deaths declining in Sub-Saharan Africa, vigilant surveillance of syphilis prevalence will be necessary to detect a potential re-emergence, as has occurred in high-income countries, and to render a timely public health response.

No association between gender inequality and peak HIV prevalence in developing countries - an ecological study

The prevalence of both gender inequality and HIV prevalence vary considerably both within all developing countries and within those in sub-Saharan Africa. We test the hypothesis that the extent of gender inequality is associated with national peak HIV prevalence. Linear regression was used to test the association between national peak HIV prevalence and three markers of gender equality - the gender-related development index (GDI), the gender empowerment measure (GEM), and the gender inequality index (GII). No evidence was found of a positive relationship between gender inequality and HIV prevalence, either in the analyses of all developing countries or those limited to Africa. In the bivariate analyses limited to Africa, there was a positive association between the two measures of gender "equality" and peak HIV prevalence (GDI: coefficient 28, 95% confidence interval (CI) 9.1-46.8; GEM: coefficient 54.8, 95% CI 20.5-89.1). There was also a negative association between the marker of gender "inequality" and peak HIV prevalence (GII: coefficient -66.9, 95% CI -112.8 to -21.0). These associations all disappeared on multivariate analyses. We could not find any evidence to support the hypothesis that variations in the extent of gender inequality explain variations in HIV prevalence in developing countries.

The Prevalence of HIV by Ethnic Group Is Correlated with HSV-2 and Syphilis Prevalence in Kenya, South Africa, the United Kingdom, and the United States

Background. This paper investigates two issues: do ethnic/racial groups with high HIV prevalences also have higher prevalences of other STIs? and is HIV prevalence by ethnic group correlated with the prevalence of circumcision, concurrency, or having more than one partner in the preceding year? Methods. We used Spearman's correlation to estimate the association between the prevalence of HIV per ethnic/racial group and HSV-2, syphilis, symptoms of an STI, having more than one partner in the past year, concurrency, and circumcision in Kenya, South Africa, the United Kingdom, and the United States. Results. We found that in each country HSV-2, syphilis, and symptomatic STIs were positively correlated with HIV prevalence (HSV-2: Kenya rho = 0.50, P = 0.207; South Africa rho-1, P = 0.000; USA rho-1, P = 0.000, Syphilis: Kenya rho = 0.33, P = 0.420; South Africa rho-1, P = 0.000; USA rho-1, P = 0.000, and STI symptoms: Kenya rho = 0.92, P = 0.001; South Africa rho-1, P = 0.000; UK rho = 0.87, P = 0.058; USA rho-1, P = 0.000). The prevalence of circumcision was only negatively associated with HIV prevalence in Kenya. Both having more than one partner in the previous year and concurrency were positively associated with HIV prevalence in all countries (concurrency: Kenya rho = 0.79, P = 0.036; South Africa rho-1, P = 0.000; UK 0.87, P = 0.058; USA rho-1, P = 0.000 and multiple partners: Kenya rho = 0.82, P = 0.023; South Africa rho-1, P = 0.000; UK rho = 0.87, P = 0.058; USA rho-1, P = 0.000). Not all associations were statistically significant. Conclusion. Further attention needs to be directed to what determines higher rates of partner change and concurrency in communities with high STI prevalence.

The changing relationship between bacterial STIs and HIV prevalence in South Africa - an ecological study

Prevalence estimates of various bacterial sexually transmitted infections in South Africa have declined considerably since the mid-1990s. Syphilis among pregnant women, for example, declined from 10.8% in 1998 to 2.8% in 2001. We used Pearson's correlation coefficients to estimate the association between the prevalence of syphilis/male urethral discharge/male genital ulcers and the peak HIV prevalence at a district and provincial level in the early and late phases of the HIV epidemic in South Africa. Prevalence estimates of syphilis, male urethral discharge and male genital ulcers during the period preceding the peak HIV prevalence were all positively correlated with the peak HIV prevalence at a provincial level (Pearson's correlation coefficient [r] = 0.83, p = 0.006; r = 0.66, p = 0.052; r = 0.79, 0.011, respectively). These relationships all switched to a negative association later in the HIV epidemic at a provincial level (r = -0.53, p = 0.14; r = -0.73, p = 0.130; r = -0.54, p = 0.027, respectively). AIDS mortality may have played an important role in the decline of bacterial sexually transmitted infections such as syphilis in this region. Consequently, the relatively recent scale-up of antiretroviral therapy may result in a resurgence of syphilis and other sexually transmitted infections as observed in high-income countries.

Migration intensity has no effect on peak HIV prevalence: an ecological study

Background

Correctly identifying the determinants of generalized HIV epidemics is crucial to bringing down ongoing high HIV incidence in these countries. High rates of migration are believed to be an important determinant of HIV prevalence. This study has two aims. Firstly, it evaluates the ecological association between levels of internal and international migration and national peak HIV prevalence using thirteen variables from a variety of sources to capture various aspects of internal and international migration intensity. Secondly, it examines the relationship between circular migration and HIV at an individual and population-level in South Africa.

Methods

Linear regression was used to analyze the association between the various measures of migration intensity and peak national HIV prevalence for 141 countries and HIV prevalence by province and ethnic group in South Africa.

Results

No evidence of a positive ecological association between national migration intensity and HIV prevalence was found. This remained the case when the analyses were limited to the countries of sub-Saharan Africa. On the whole, countries with generalized HIV epidemics had lower rates of internal and external migration. Likewise, no association was found between migration and HIV positivity at an individual or group-level in South Africa.

Conclusion

These results do not support the thesis that migration measured at the country level plays a significant role in determining peak HIV prevalence.

HIV prevalence by race co-varies closely with concurrency and number of sex partners in South Africa

BACKGROUND

HIV prevalence differs by more than an order of magnitude between South Africa's racial groups. Comparing the sexual behaviors and other risk factors for HIV transmission between the different races may shed light on the determinants of South Africa's generalized HIV epidemic.

METHODS

Five nationally representative and one city-representative population-based surveys of sexual behavior were used to assess the extent to which various risk factors co-varied with HIV prevalence by race in South Africa.

RESULTS

In 2004, the prevalence of HIV was 0.5%, 1%, 3.2% and 19.9% in 15-49 year old whites, Indians, coloureds and blacks respectively. The risk factors which co-varied with HIV prevalence by race in the six surveys were age of sexual debut (in five out of five surveys for men and three out of six surveys for women), age gap (zero surveys in men and three in women), mean number of sex partners in the previous year (five surveys in men and three in women) and concurrent partnerships (five surveys in men and one in women). Condom usage and circumcision were both more prevalent in the high HIV prevalence groups. The reported prevalence of concurrency was 6 to 17 times higher in the black as opposed to the white men in the five surveys.

CONCLUSIONS

The differences in sexual behavior in general, and the prevalence of concurrency and the number of sexual partners in particular, offer a plausible and parsimonious cause to explain a part of the differing prevalences of HIV between South Africa's racial groups.