Science : Une solution mathématique au VIH ?


Cette semaine dans le très prestigieux Lancet, L'OMS propose une stratégie permettant théoriquement de réduire la prévalence du SIDA à 1% d'ici 50 ans. De réduire la moratlité et l'incidence de la maladie à moins de 1/1000 d'ici 2016, le tout dans le cadre d'une stratégie rentable financièrement à partie de 2032.
Le principe : dépistage massif sur la base du volontariat et traitement immédiat (anti-retroviral) si positif.
Comment ont-ils abouti à ce résultat : par des modèles mathématiques.
Plus précisément des modèles stocchastiques à partir des données disponibles en Afrique du Sud et générées par Visual Basic (microsoft 2002).

Abstract et un bout du materiel et methode ci dessous :

Abstract :
Lancet. 2008 Nov 25

Universal voluntary HIV testing with immediate antiretroviral therapy as a strategy for elimination of HIV transmission: a mathematical model.

Granich RM, Gilks CF, Dye C, De Cock KM, Williams BG.

Department of HIV/AIDS, WHO, Geneva, Switzerland.

Roughly 3 million people worldwide were receiving antiretroviral therapy (ART) at the end of 2007, but an estimated 6.7 million were still in need of treatment and a further 2.7 million became infected with HIV in 2007. Prevention efforts might reduce HIV incidence but are unlikely to eliminate this disease. We investigated a theoretical strategy of universal voluntary HIV testing and immediate treatment with ART, and examined the conditions under which the HIV epidemic could be driven towards elimination.

METHODS: We used mathematical models to explore the effect on the case reproduction number (stochastic model) and long-term dynamics of the HIV epidemic (deterministic transmission model) of testing all people in our test-case community (aged 15 years and older) for HIV every year and starting people on ART immediately after they are diagnosed HIV positive. We used data from South Africa as the test case for a generalised epidemic, and assumed that all HIV transmission was heterosexual.

FINDINGS: The studied strategy could greatly accelerate the transition from the present endemic phase, in which most adults living with HIV are not receiving ART, to an elimination phase, in which most are on ART, within 5 years. It could reduce HIV incidence and mortality to less than one case per 1000 people per year by 2016, or within 10 years of full implementation of the strategy, and reduce the prevalence of HIV to less than 1% within 50 years. We estimate that in 2032, the yearly cost of the present strategy and the theoretical strategy would both be US$1.7 billion; however, after this time, the cost of the present strategy would continue to increase whereas that of the theoretical strategy would decrease.

INTERPRETATION: Universal voluntary HIV testing and immediate ART, combined with present prevention approaches, could have a major effect on severe generalised HIV/AIDS epidemics. This approach merits further mathematical modelling, research, and broad consultation.

Début du matériel et méthode :

In the stochastic model, we chose an initial value for a person’s CD4+ cell count and a survival time, which were taken from population distributions derived from vailable data. For the pre-infection distribution of CD4+ cell counts (figure 1A) we used data from a survey in Orange Farm, South Africa.29 We assumed that the CD4+ cell count decreased by 25% immediately after infection and linearly thereafter.29 Every month, the index case could infect another person, be tested for HIV, or, if HIV positive, start treatment at a preset CD4+ cell count. We assumed that survival after infection with HIV, without ART, would follow a Weibull distribution29 (figure 1B) with a mean of 11 (SD 0·5) years.31 The acute phase would last for 2 months, during which time the infectivity would be ten times higher than in the chronic phase (figure 1C).32,33 The fi nal phase would last for 5% of the survival time without ART, during which time the infectivity would be five times ...

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