The Non-Linear Transmission Dynamics of HIV/AIDS

How infectious a person is when infected with HIV depends upon what stage of the disease the person is in. We use three stages which we call primary, asymptomatic and symptomatic. It is important to have a systematic method for computing all three infectivities so that the measurements are comparable. Using robust modeling we provide high-resolution estimates of semen infectivity by HIV disease stage. We find that the infectivity of the symptomatic stage is far higher, hence more potent, than the values that prior studies have used when modeling HIV transmission dynamics. The stage infectivity rates for semen are 0.024, 0.002, 0.299 for primary, asymptomatic and symptomatic (late-stage) respectively. Implications of our infectivity estimates and modeling for understanding heterosexual epidemics such as the Sub-Saharan African one are explored. Most models are compartment models that are based on the number of new infections per unit time. We create a new risk-based model that focuses on a susceptible person's risk of becoming infected if he has a single contact with an infected individual

Untangling the Interplay between Epidemic Spread and Transmission Network Dynamics

The epidemic spread of infectious diseases is ubiquitous and often has a considerable impact on public health and economic wealth. The large variability in the spatio-temporal patterns of epidemics prohibits simple interventions and requires a detailed analysis of each epidemic with respect to its infectious agent and the corresponding routes of transmission. To facilitate this analysis, we introduce a mathematical framework which links epidemic patterns to the topology and dynamics of the underlying transmission network. The evolution, both in disease prevalence and transmission network topology, is derived from a closed set of partial differential equations for infections without allowing for recovery. The predictions are in excellent agreement with complementarily conducted agent-based simulations. The capacity of this new method is demonstrated in several case studies on HIV epidemics in synthetic populations: it allows us to monitor the evolution of contact behavior among healthy and infected individuals and the contributions of different disease stages to the spreading of the epidemic. This gives both direction to and a test bed for targeted intervention strategies for epidemic control. In conclusion, this mathematical framework provides a capable toolbox for the analysis of epidemics from first principles. This allows for fast, in silico modeling - and manipulation - of epidemics and is especially powerful if complemented with adequate empirical data for parameterization

Towards targeted screening for acute HIV infections in British Columbia

<p>Abstract</p> <p>Background</p> <p>Our objective was to describe the characteristics of acute and established HIV infections diagnosed in the Canadian province of British Columbia. Province-wide HIV testing and surveillance data were analyzed to inform recommendations for targeted use of screening algorithms to detect acute HIV infections.</p> <p>Methods</p> <p>Acute HIV infection was defined as a confirmed reactive HIV p24 antigen test (or HIV nucleic acid test), a non-reactive or reactive HIV EIA screening test and a non-reactive or indeterminate Western Blot. Characteristics of unique individuals were identified from the British Columbia HIV/AIDS Surveillance System. Primary drug resistance and HIV subtypes were identified by analyzing HIV <it>pol </it>sequences from residual sera from newly infected individuals.</p> <p>Results</p> <p>From February 2006 to October 2008, 61 individuals met the acute HIV infection case definition, representing 6.2% of the 987 newly diagnosed HIV infections during the analysis period. Acute HIV infection cases were more likely to be men who have sex with men (crude OR 1.71; 95% CI 1.01-2.89], to have had a documented previous negative HIV test result (crude OR 2.89; 95% CI 1.52-5.51), and to have reported a reason for testing due to suspected seroconversion symptoms (crude OR 5.16; 95% CI 2.88-9.23). HIV subtypes and rates of transmitted drug resistance across all classes of drugs were similar in persons with both acute and established HIV infections.</p> <p>Conclusions</p> <p>Targeted screening to detect acute HIV infection is a logical public health response to the HIV epidemic. Our findings suggest that acute HIV infection screening strategies, in our setting, are helpful for early diagnosis in men who have sex with men, in persons with seroconversion symptoms and in previously negative repeat testers.</p

HIV transmission risk through anal intercourse: systematic review, meta-analysis and implications for HIV prevention

Background The human immunodeficiency virus (HIV) infectiousness of anal intercourse (AI) has not been systematically reviewed, despite its role driving HIV epidemics among men who have sex with men (MSM) and its potential contribution to heterosexual spread. We assessed the per-act and per-partner HIV transmission risk from AI exposure for heterosexuals and MSM and its implications for HIV prevention

Remedial post-secondary education and subsequent college-level performance: a comparative study

The purpose of this study was to examine the relationship between remedial instruction in a mathematics course, Basic Algebra, offered at Rowan College, and subsequent performance in a first college-level math course. The subjects utilized in the study consisted of remedial attendees or students who completed the course, test-outs, or students who were placed into the course but tested out of it, and non-remedial students, or those who never needed the course. Mean grades for each of the three groups were then computed. A chi-square analysis indicated no significant difference between the three groups. Based on the findings, the decision was made to retain the null for hypothesis I which stated there would be no significant difference between the attendees and the test-outs. The null was rejected for hypothesis I and the alternate hypothesis, which stated there would be no significant difference between the remedial attendees and the non-remedial students, was retained

The San Francisco MSM Epidemic: A Retrospective Analysis

We investigate various scenarios for ending the San Francisco MSM (men having sex with men) HIV/AIDS epidemic (1978–1984). We use our previously developed model and explore changes due to prevention strategies such as testing, treatment and reduction of the number of contacts. Here we consider a “what-if” scenario, by comparing different treatment strategies, to determine which factor has the greatest impact on reducing the HIV/AIDS epidemic. The factor determining the future of the epidemic is the reproduction number R0; if R0 &lt; 1, the epidemic is stopped. We show that treatment significantly reduces the total number of infected people. We also investigate the effect a reduction in the number of contacts after seven years, when the HIV/AIDS threat became known, would have had in the population. Both reduction of contacts and treatment alone, however, would not have been enough to bring R0 below one; but when combined, we show that the effective R0 becomes less than one, and therefore the epidemic would have been eradicated

Transmission Probabilities and Reproduction Numbers for Sexually Transmitted Infections with Variable Infectivity: Application to the Spread of HIV Between Low- and High-Activity Populations

Probabilities of transmission and numbers of secondary cases are given for an infection which is transmitted sexually by individuals engaged in multiple partnerships with specified durations and timings. The results applied to the human immunodeficiency virus (HIV) hinge on a function which captures the dependence of the per coital act probability of transmission on the time since disease onset and on the duration of infection at death. Reproduction numbers are derived in a heterogeneous population consisting of low- and high-activity men and women. An expression for the basic reproduction number R0 of this system sheds light on the role of concurrency, on the timing of the partnerships, and on bridging effects. A high-activity group can cause a significant epidemic outbreak no matter how small the bridging effect, as long as it is not 0. Only if the bridging effect is eliminated altogether can the growth factor in the low-activity group be reduced independently of what happens in the high-activity group. The role of the relationship between client and sex worker and the role of bridging populations in sub-Saharan Africa are assessed.basic reproduction number, heterogeneous populations, HIV, transmission probability,