The epidemic dynamics of HIV-1 in Italy: modelling the interaction between intravenous drug users and heterosexual population

A simple model of HIV epidemic in Italy: The role of the antiretroviral treatment

In the present paper we propose a simple time-varying ODE model to describe the evolution of HIV epidemic in Italy. The model considers a single population of susceptibles, without distinction of high-risk groups within the general population, and accounts for the presence of immigration and emigration, modelling their effects on both the general demography and the dynamics of the infected subpopulations. To represent the intra-host disease progression, the untreated infected population is distributed over four compartments in cascade according to the CD4 counts. A further compartment is added to represent infected people under antiretroviral therapy. The per capita exit rate from treatment, due to voluntary interruption or failure of therapy, is assumed variable with time. The values of the model parameters not reported in the literature are assessed by fitting available epidemiological data over the decade 2003÷2012. Predictions until year 2025 are computed, enlightening the impact on the public health of the early initiation of the antiretroviral therapy. The benefits of this change in the treatment eligibility consist in reducing the HIV incidence rate, the rate of new AIDS cases, and the rate of death from AIDS. Analytical results about properties of the model in its time-invariant form are provided, in particular the global stability of the equilibrium points is established either in the absence and in the presence of infected among immigrants.

Recent trends in the HIV epidemic among injecting drug users in Northern Italy, 1993-1999

OBJECTIVE

To monitor and describe the time trends of the HIV epidemic among intravenous drug users (IDU) attending drug dependence treatment centres (DDTC) in Northern Italy.

DESIGN

A cohort of all seronegative IDU attending DDTC in Lombardy between 1993 and 1999; all had been tested for HIV at least twice. Periodic sample interview surveys were done to assess risk behaviours.

METHODS

The incidence rates of HIV infection were calculated using the person-year (PY) method and expressed as the number of cases per 1000 PY at risk. Background HIV prevalence was calculated by dividing the number of positive cases by the total number of IDU tested at all DDTC in Lombardy.

RESULTS

Between 1993 and 1999, 135 seroconversions occurred in 7945 subjects followed for 19 671 PY, yielding an incidence rate of 6.9/1000 PY. Ninety seroconversions occurred among the 6563 males and 45 seroconversions among 1382 females (incidence rates 5.5 and 14.0, respectively). Among the males, the incidence of HIV was 4.5 in those aged less than 25 years and 5.8 in those aged 25 years or more. Among the females, the corresponding figures were 21.1 and 10.3. HIV prevalence decreased over time, and it was higher among females. Sexual behaviours at risk were more common among females.

CONCLUSIONS

The incidence of HIV infection among IDU in Northern Italy was stable between 1993 and 1999. The higher incidence and prevalence among females and the different prevalence of risk behaviours between genders suggest an increasing role of heterosexual transmission.

The changing distribution of HIV infection: HIV surveillance in Lazio, Italy, 1985 through 1994. Lazio HIV Surveillance Collaborative Group

OBJECTIVES

This study sought to describe the human immunodeficiency virus (HIV) surveillance system in Lazio, Italy, and to analyze exposure patterns and time trends of HIV serodiagnoses from January 1985 to December 1994.

METHODS

A linkage procedure made it possible to identify newly diagnosed HIV cases. Anonymous information was collected on demographic and exposure factors for each individual.

RESULTS

Of 35,425 reports, 13,660 were newly diagnosed HIV cases, 70.9% of them in men. The proportion of women increased at the beginning of the study period (the male:female ratio declined from 3.5 in 1985 to 2.6 in 1986) and then remained stable. The proportion of subjects reporting heterosexual exposure, in men and women, respectively, increased from 1.5% and 2.0% in 1985 to 21.2% and 60.8% in 1994. Starting in 1992, heterosexual contact has become the main transmission route for women.

CONCLUSIONS

A changing pattern in the HIV epidemic is emerging, with a shift in the incidence of HIV diagnosis from "core" high-risk groups (drug injectors) to the large low-risk population (the general population) exposed through heterosexual transmission. This is probably occurring in other areas (e.g., large urban centers in the United States) with a similar epidemiological situation.

Deliveries, abortion and HIV-1 infection in Rome, 1989-1994. The Lazio AIDS Collaborative Group

The prevalence of HIV-1 among women of reproductive age is currently estimated at the time they give birth. We assessed HIV-1 prevalence at the end of pregnancy, whether they delivered or had an induced or spontaneous abortion. Women admitted at the end of pregnancy to hospitals in the Lazio Region, Italy, were tested for antibodies to HIV-1. Consent for testing was granted by 97.1% of 218,357 subjects; women who did not consent were tested anonymously. The prevalences of infection were 0.34% in 1989, 0.38% in 1990, 0.28% in 1991, 0.23% in 1992, 0.28% in 1993, and 0.24% in 1994. Significantly higher prevalences of infection were associated with induced abortion (0.49%) than with delivery (0.18%; OR: 2.72; 95% CI: 2.29-3.22) and among women who refused (0.85%) than among those who consented to testing (0.27%; OR: 3.14; 95% CI: 2.35-4.19). A significant temporal reduction in prevalence was observed only among women who delivered (0.15% in 1993 and 1994; 0.26% in 1989 and 1990). The prevalence of HIV-1 infection is thus higher among women undergoing induced abortions than among those who deliver and higher among women who refuse testing than among those who consent. Studies confined to neonatal testing or to voluntary testing of pregnant women would thus underestimate the prevalence of HIV-1 among women of reproductive age.

A persistent rise in mortality among injection drug users in Rome, 1980 through 1992

OBJECTIVES

The purpose of the study was to analyze overall and cause-specific mortality among injection drug users in Rome.

METHODS

A cohort of 4200 injection drug users was enrolled in drug treatment centers from 1980 through 1988 and followed up until December 1992.

RESULTS

The age-adjusted mortality rate from all causes increased from 7.8/1000 person-years in 1985/86 to 27.7/1000 in 1991/92. The rise was mainly attributable to acquired immunodeficiency syndrome (AIDS), but mortality from overdose and other causes increased as well. The cumulative risk of death by the age of 40 was 29.3%.

CONCLUSIONS

The impact of AIDS deaths appears to be additional to a persistent increase of mortality for all other causes.

The HIV/AIDS epidemics among drug injectors: a study of contact structure through a mathematical model

Numerical results of a model with variable infectivity for the dynamics of HIV/AIDS (human immunodeficiency virus/acquired immune deficiency syndrome) have been compared with the data of AIDS cases among intravenous drug users in Italy, especially in the Latium region. We examined several hypotheses about the dynamics of the epidemics; for each we obtained, mainly through a least-square approach but also minimizing a different quantity, a best-fit estimate of the parameters. In the simplest model, the population is assumed to be homogeneous, and we estimate contact rate and year of start of the epidemics, obtaining a good fit up to 1989, less so after. A substantial increase in fit is obtained in assuming either a decrease of the contact rate over time or a heterogeneous population with a smaller active group. We have also compared models with different infectivity curves during the incubation period: the assumption of constant infectivity is untenable, whereas the often suggested hypothesis of a peak in infectivity shortly after infection seems to be in agreement with data.

HIV risk-related behaviors among injection drug users in Rome: differences between 1990 and 1992

Temporal differences in human immunodeficiency virus (HIV) risk-related behaviors among injection drug users in Rome, Italy, were analyzed in 487 drug users recruited in 1990 and 450 recruited in 1992. Sharing of syringes decreased among self-reported HIV-positive drug users between 1990 and 1992, but there was no change in their sexual behavior. Fewer HIV-seronegative drug users reported passing on used syringes in 1992 than in 1990; however, there was no change in the percentage of seronegative subjects using previously used syringes, and a reduction in condom use with primary partners. There still exists a great potential for transmission of HIV infection among injection drug users and from injection drug users to the general population.