Injecting drug users more likely to progress to AIDS even if taking HAART

Michael Carter
Published: 08 January 2004

HIV-positive injecting drug users are significantly more likely to develop an AIDS defining illness, even when they are taking HAART, than HAART-treated HIV-positive individuals who do not inject drugs, according to research conducted at Johns Hopkins University and published in the January 1st edition of the Journal of Acquired Immune Deficiency Syndromes.

The Baltimore investigators conducted a longitudinal study involving 827 HIV-positive injecting drug users and 1314 HIV-positive individuals who did not inject drugs who received free HIV care from the Johns Hopkins AIDS Service.

The incidence of AIDS-defining events was calculated on a biannual basis from 1995 to 2002 for both injecting drug users and individuals who did not inject drugs. The results were adjusted for age, sex, race, baseline CD4, baseline HIV viral load, and AIDS -defining events prior to enrollment.

A second analysis was performed by the investigators which compared the risk of developing an AIDS-defining illness in 1999 or later. This analysis was adjusted for all the variables used in the earlier analysis as well as use of antiretroviral drugs before HAART became available, whether HIV was suppressed to below 400 copies/mL, whether durable HIV suppression was achieved, and the total duration of HAART.

At baseline injecting drug users were significantly likely to be younger (37 years versus 40 years, p<0.01), African Americans (85% versus 66%, p<0.01), and to have taken less HAART (739 days of therapy versus 899 days, p<0.001). Baseline CD4 cell count and viral load were comparable.

There was a significant fall in the biannual incidence of AIDS-defining events from 1995 to 2002. However, the magnitude of the decrease was less in injecting drug users than in individuals who did not inject drugs (31.9 per 100 person years to 16.2 per 100 person years, versus 37.00 per 100 person years to 9.7 cases per 100 person years).

The incidence ratio (calculated as the incidence amongst injecting drug users divided by the incidence amongst non-injecting drug users) increased from 1995-96, the last pre-HAART period, to 2001-02. In 1995-96 the incidence ratio adjusted for age, sex, baseline CD4 cell count, and viral load was 1.03, and this increased to 1.66 in 2001-02.

When the investigators looked at the risk of developing an AIDS-defining illness and injecting drug use in 1999, they found that the risk ratio was 1.45, indicating that the injecting drug users were 45% more likely to develop an AIDS-defining illness than non-injecting drug users in 1998 or later.

Other factors found to be associated with an increased risk of developing an opportunistic infection included a baseline CD4 cell count below 200 cells/mm3, a baseline viral load above 100,000 copies/mL, an earlier AIDS-defining event, earlier suboptimal antiretroviral therapy, and the use of salvage therapy.

When the investigators compared the HIV viral loads of injecting drug users with those of individuals who did not inject drugs, they found that injecting drug users were less likely to achieve a viral load of below 400 copies/mL (43% versus 56%) or to maintain suppression (43% versus 49%).

Finally, the investigators looked at the types of AIDS-defining illness which patients in their cohort developed. They found that injecting drug users were more likely to develop both opportunistic infections which occur earlier in the course of HIV infection (such as candidia and bacterial pneumonia), and infections which characterise more advanced HIV disease (such as PCP and MAC).

"Our current analysis demonstrated that over the long term, IDUs received relatively less benefit from [HA]ART than patients who have other HIV transmission factors", note the investigators. They add, "in fact, our data indicate that the difference between IDUs and non-IDUs in clinical event rates progressively increased over time."

An earlier study conducted by the Baltimore investigators found that injecting drug users had poorer adherence to HAART, and they speculate that this could explain the higher incidence of AIDS-defining illnesses amongst this patient group in the HAART era. The add, “however, other factors, such as poorer immune response related to illicit drug use, may also serve as barriers to effective antiretroviral therapy for IDUs.”

Further information on this website

Reference

Moore RD et al. Differences in HIV disease progression by injecting drug use in HIV-infected persons in care. JAIDS 35: 46 – 51, 2004.

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