HIV and concurrent sexual partnerships: modelling the role of coital dilution

Sawers, Larry; Isaac, Alan G.; Stillwaggon, Eileen

doi:10.1186/1758-2652-14-44

Cited by 33 publications

(30 citation statements)

References 34 publications

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“…More precisely, we multiply the monthly transmission probability by 0.8 if the index person has two partners, and by 0.6 if he or she has three partners. These assumptions imply that more concurrency is associated with a larger number of coital acts in the simulated population, and differ from another coital dilution modeling study that rests on the stronger assumption that higher levels of concurrency lead to a reduction in the population-level number of coital acts (Sawers, Isaac, and Stillwaggon 2011).…”

Section: Figurementioning

confidence: 86%

Sexual networks, partnership mixing, and the female-to-male ratio of HIV infections in generalized epidemics

Reniers¹,

Armbruster²,

Lucas³

2015

DemRes

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BACKGROUNDEmpirical estimates of the female-to-male ratio of infections in generalized HIV epidemics in sub-Saharan Africa range from 1.31 in Zambia to 2.21 in Ivory Coast. Inequalities in the gender ratio of infections can arise because of differences in exposure (to HIV-positive partners), susceptibility (given exposure), and survival (once infected). Differences in susceptibility have to date received most attention, but neither the relatively high gender ratio of infections nor the heterogeneity in empirical estimates is fully understood. OBJECTIVEDemonstrate the relevance of partnership network attributes and sexual mixing patterns to gender differences in the exposure to HIV-positive partners and the gender ratio of infections. METHODAgent-based simulation model built in NetLogo. RESULTSThe female-to-male ratio of infections predicted by our model ranges from 1.13 to 1.75. Gender-asymmetric partnership concurrency, rapid partnership turnover, elevated partnership dissolution in female-positive serodiscordant couples, and lower partnership re-entry rates among HIV-positive women can produce (substantial) differences in the gender ratio of infections. Coital dilution and serosorting have modest moderating effects. CONCLUSIONPartnership network attributes and sexual mixing patterns can have a considerable effect on the gender ratio of HIV infections. We need to look beyond individual behavior and gender differences in biological susceptibility if we are to fully understand, and remedy, gender inequalities in HIV infection in generalized epidemics.

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Section: Figurementioning

confidence: 86%

Sexual networks, partnership mixing, and the female-to-male ratio of HIV infections in generalized epidemics

Reniers¹,

Armbruster²,

Lucas³

2015

DemRes

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“…In other words, if a person has 10 times as many simultaneously sexual partners, conventional model approaches may implicitly assume that each person has 10 times as many sexual encounters in a particular time period. However, data suggest that people with many simultaneous partners do not have a proportionate increase in frequency of sexual encounters per unit time, and therefore this implicit assumption may exaggerate the impact of concurrency on transmission risk [30]. …”

Section: Methodsmentioning

confidence: 99%

How do different eligibility guidelines for antiretroviral therapy affect the cost–effectiveness of routine viral load testing in sub-Saharan Africa?

Braithwaite

Nucifora

Toohey

et al. 2014

Aids

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Background Increased eligibility guidelines of antiretroviral therapy (ART) may lead to greater routine viral load monitoring. However, in resource-constrained settings, the additional resources required by greater routine viral load monitoring may impair ability to comply with expanded eligibility guidelines for ART. Objective We use a published validated computer simulation of the HIV epidemic in East African countries (expanded to include transmission as well as disease progression) to evaluate the cost–effectiveness of routine viral load monitoring. Methods We explored alternative scenarios regarding cost, frequency, and switching threshold of routine viral load monitoring (including every 6 or every 12 months; and switching thresholds of 1000, or 10 000 copies/ml), as well as alternative scenarios regarding ART initiation (200, 350, 500 cells/μl, and no CD4+ cell threshold). For each ART initiation strategy, we sought to identify the viral load monitoring strategy at which the incremental cost–effectiveness ratio (ICER) of more frequent routine viral load testing became more favorable than the ICER of more expansive ART eligibility. Cost inputs were based on data provided by the Academic Model Providing Access to Healthcare (AMPATH), and disease progression inputs were based on prior published work. We used a discount rate of 3%, a time horizon of 20 years, and a payer perspective. Results Across a wide range of scenarios, and even when considering the beneficial effect of virological monitoring at reducing HIV transmission, earlier ART initiation conferred far greater health benefits for resources spent than routine virological testing, with ICERs of approximately $1000 to $2000 for earlier ART initiation, versus ICERs of approximately $5000 to $25 000 for routine virological monitoring. ICERs of viral load testing were insensitive to the cost of the viral load test, because most of the costs originated from the downstream higher costs of later regimens. ICERs of viral load testing were very sensitive to the relative cost of second-line compared with first-line regimens, assuming favorable value when the costs of these regimens were equal. Conclusion If all HIV patients are not yet treated with ART starting at 500 cells/μl and costs of second regimens remain substantially more expensive than first-line regimens, resources would buy more population health if they are spent on earlier ART rather than being spent on routine virological testing.

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“…Coital dilution is the reduction in the number of sexual acts per partner when an additional, concurrent partner is added [1]. Concurrency is defined as having two or more sexual partnerships overlapping in time [2].…”

Section: Introductionmentioning

confidence: 99%

“…A common assumption in mathematical models is to preserve the number of acts per partnership under concurrency [3], but that implies the number of potential transmission events increases linearly with degree (the number of ongoing partners at any time). One model testing this assumption suggested that relatively modest levels of dilution (25% or higher) could erase the effects of concurrency [1], though the assumptions of this model also led to decreasing rates of activity over time.…”

Section: Introductionmentioning

confidence: 99%

Minimal Coital Dilution in Accra, Ghana

Jenness

Biney

Ampofo

et al. 2015

JAIDS Journal of Acquired Immune Deficiency Syndromes

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Background Coital dilution, the reduction in the coital frequency per partner when an additional ongoing partner is added, may reduce the transmission potential of partnership concurrency for HIV and other sexually transmitted infections. Empirical estimates of dilution, especially dilution of sexual acts unprotected by condoms, are needed to inform prevention research. Methods Sexually active adults in Accra, Ghana were recruited in a multi-stage household probability sample. Degree (number of ongoing partners), total acts, and unprotected acts were measured retrospectively for each month in the past year through an event-history calendar. Random effects negative binomial models estimated the association between degree and coital frequency. Results Compared to person-months with a single partner (monogamy), 2.06 times as many total acts and 1.94 times as many unprotected acts occurred in months with 2 partners. In months with 3 partners, 2.90 times as many total acts and 2.39 times as many unprotected acts occurred compared to monogamous months. Total acts but not unprotected acts also declined with partnership duration. Conclusions No dilution was observed for total acts with up to three concurrent partners, but a small amount of dilution was observed for unprotected acts for months with multiple concurrencies. This suggests moderate selective condom use in months with multiple concurrencies. The implications of the observed dilution for future HIV transmission must be investigated with mathematical models.

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HIV and concurrent sexual partnerships: modelling the role of coital dilution

Cited by 33 publications

References 34 publications

Sexual networks, partnership mixing, and the female-to-male ratio of HIV infections in generalized epidemics

Sexual networks, partnership mixing, and the female-to-male ratio of HIV infections in generalized epidemics

How do different eligibility guidelines for antiretroviral therapy affect the cost–effectiveness of routine viral load testing in sub-Saharan Africa?

Minimal Coital Dilution in Accra, Ghana

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