[Todos] Conferencia Prof. Joao AMARAL

[Vera H.]

El  INSTITUTO DE CALCULO  invita a la

Conferencia del Profesor Joao AMARAL

Departmento de Matematica, Instituto Superior Tecnico, Lisboa, Portugal


el dia Viernes 15 de Octubre a las 16:30 hs. :

. "Projections of HIV/AIDS cases in Portugal"


INTRODUCTION: A statistical procedure called Back-calculation has been a
widely used method to estimate the size of the population with HIV/AIDS.
Recent discussions suggest that this method should be adapted to take into
account the effect of treatment. The aim of this study is to use that method and
a worst-case scenario, in order to assess the quality of previous
projections and obtain new ones.

METHODOLOGY: The AIDS incidence data was adjusted taking into account
reporting delays, no reporting and underrreporting. A conditional likelihood
estimation of the reporting delay distribution was performed using standard
algorithms for Piosson regression. Then lower bounds on the size of the AIDS
epidemic were obtained. A Weibull and Gamma distribution were considered for
the latency period distribution.  The EM algorithm was applied to obtain
maximum likelihood estimates of the HIV incidence.  The density of infection
times was parametrized as a step function.  The National AIDS/HIV database
was used ande the methodology was applied four different transmission
categories, injecting drug users (IDU), Heterosexual, Homo/Bisexual and
"Other", to obtain short-term projections (2002-2005) and an estimate of the
of the minimum size of the epidemic.

RESULTS: 2002-2005 projections show an annual decrease of new AIDS cases fot
the IDU and the Homo/Bisexual transmission categories. For the year 2003 (in
comparison with 2002) a decrease of 7.3% is expected in IDU. In this
category the number of new cases is estimated to decrease by 9.5% in 2004
and to suffer a further decrease of 11.8% in the year 2005.
However, the Heterosexual and the "Other" are estimated to increase. In the
first category the increase rate is not very pronounced: in 2003 the
incidence is 5.5% higher than the estimated for 2002, in 2004 is 3.5% higher
when compared to 2003 and 1.3% in 2005 relatively to 2004. In the second the
expected annual increase rate for the number of new AIDS cases is very
significant: in 2003 the incidence rises 36% compared to 2002, in 2004 29%
higher than in 2003 and in 2005 23.3% higher than 2004.

CONCLUSIONS: This study outlines a methodology for obtaining projections on
the size of the AIDS epidemic. It producess a lower bound, since it only
estimates the cumulative number of individuals that will eventually develop
AIDS from those already infected with HIV are obtained.
The projections indicate for the the next few years: an increase in the
annual number of AIDS new cases in the Heterosexual and "Other"transmission
categories, with special incidence on this last one; a slowing down on the
annual number of new AIDS cases in the IDU transmission category; an
apparent change on the decrease tendency in the Homo/Bisexual category.

These projections indicate that HIV/AIDS will remain a public health problem
in Portugal.


Instituto de Calculo
Fac. de Cs. Exactas y Naturales
Pabellón II, 2do. Piso 
Ciudad Universitaria 

Viernes 15 de Ocutbre de 2004
a las 16:30 hs. 
TE: 4 576-3375

QUEDAN   TODOS   CORDIALMENTE   INVITADOS

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