CROI: TB in HIV patients in UK highest amongst black Africans and those with low CD4 cell count

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Black Africans, and patients with a low CD4 cell count are the groups of HIV-positive individuals with the greatest risk of tuberculosis in the UK, according to a study presented to the recent Fourteenth Conference on Retroviruses and Opportunistic Infections in Los Angeles. The study also found that African patients often had their tuberculosis diagnosed soon after they were diagnosed with HIV.

Tuberculosis is the leading cause of illness and death amongst HIV-positive individuals around the world, an is a particular issue in sub-Saharan Africa, and a growing proportion of HIV-positive patients in the UK originate from this region.

Investigators from the UK CHIC (Collaborative HIV Cohort) wished to determine the incidence of tuberculosis in African and non-African patients receiving care from HIV clinics in the UK, and to compare the incidence of the tuberculosis before and after patients started potent antiretroviral therapy.

Glossary

person years

In a study “100 person years of follow-up” could mean that information was collected on 100 people for one year, or on 50 people for two years each, or on ten people over ten years. In practice, each person’s duration of follow-up is likely to be different.

multivariate analysis

An extension of multivariable analysis that is used to model two or more outcomes at the same time.

opportunistic infection (OI)

An infection that occurs more frequently or is more severe in people with weakened immune systems, such as people with low CD4 counts, than in people with healthy immune systems. Opportunistic infections common in people with advanced HIV disease include Pneumocystis jiroveci pneumonia; Kaposi sarcoma; cryptosporidiosis; histoplasmosis; other parasitic, viral, and fungal infections; and some types of cancer. 

observational study

A study design in which patients receive routine clinical care and researchers record the outcome. Observational studies can provide useful information but are considered less reliable than experimental studies such as randomised controlled trials. Some examples of observational studies are cohort studies and case-control studies.

immune system

The body's mechanisms for fighting infections and eradicating dysfunctional cells.

The UK CHIC is an ongoing observational cohort study involving HIV-positive patients receiving care at ten large treatment centres. A total of 22,207 individuals who received care between 1996 and 2005 were included in the investigators’ current analysis.

Baseline median age was broadly similar across ethnicities (mid-30s), but African patients were less likely to be male (36%, versus 92% of white patients and 80% of patients of other ethnicities). African patients also had lower CD4 cell counts on entry to the cohort (median 256 cells/mm3, versus 341 cells/mm3 for white patients, and 330 cells/mm3 for patients of other ethnicities), and started anti-HIV treatment with lower median CD4 cell counts (151 cells/mm3, versus 195 cells/mm3 for white patients and 173 cells/mm3 for patients of other ethnicities).

One or more episode of tuberculosis were experienced by 805 patients. More black African patients (494 of 5,055, 10%) were diagnosed with tuberculosis than any other ethnic group (white patients, 185 of 13,056, 1%; other ethnic groups, 126 of 4,960 patients, 3%).

Black African patients were diagnosed with tuberculosis sooner after entering HIV care than other groups. Median time from HIV diagnosis to first tuberculosis episode was less than a month for African patients, compared to just over 38 months for white patients and a little less than eight months for patients of other ethnicities.

Amongst patients taking potent antiretroviral therapy, the incidence of tuberculosis was 1.5 per 100 person years amongst white patients, 3.5 per 100 person years amongst patients of other ethnicities, but 7.4 per 100 person years amongst black Africans.

Multivariate analysis showed that, compared to white patients, black Africans had an adjusted risk ratio of tuberculosis of 2.49. Unsurprisingly, the strength of the immune system was a significant factor determining the risk of tuberculosis, with tuberculosis risk increasing with lower CD4 cell counts. Compared to those with a CD4 cell count above 500 cells/mm3, patients with a CD4 cell count between 350 – 499 cells/mm3 had an adjusted tuberculosis risk ratio of 2.89, compared to an adjusted risk ratio of 10.81 for patients with a CD4 cell count between 51 – 199 cells/mm3, and an adjusted risk ratio of 33.92 for patients with a CD4 cell count below 50 cells/mm3.

“Black African ethnicity and low CD4 cell count are the main risk factors for tuberculosis incidence among people attending UK HIV clinics”, conclude the investigators. They add, “most tuberculosis episodes in black Africans are close to the first clinic visit” and “earlier HIV diagnosis is needed so that interventions can be implemented prior to a first tuberculosis episode.”

References

Grant A et al. TB incidence among HIV-infected Africans in the United Kingdom. Fourteenth Conference on Retroviruses and Opportunistic Infections, abstract 846, Los Angeles, 2007.