TB incidence lower with ART in rich countries, but not at age 50+
Tuberculosis incidence was 44% lower in HIV-positive people in high-income countries who started antiretroviral therapy (ART) than in those who did not. But the protective effect of ART did not extend to people older than 50 or with a CD4 count below 50 cells/μL.
Much research on the impact of ART on TB comes from low- and
middle-income countries. This HIV-CAUSAL Collaboration
involved 65,121 antiretroviral-naive people in 12 cohorts from
the United States and Europe. No one had AIDS and everyone was
18 or older.
The researchers excluded 206 people diagnosed with TB within
the first month of follow-up to prevent inclusion of patients
with prevalent TB instead of incident TB. Follow-up extended
from 1996 through 2007.
Over a median follow-up of 28 months, TB developed in 712
people to yield an incidence of 3.0 cases per 1000
person-years. Overall TB risk was 44% lower in people who
started ART than in those who did not (hazard ratio [HR] 0.56,
95% confidence interval [CI] 0.44 to 0.72).
But TB incidence was not lower in people over 50 who started
ART than in those who did not (HR 1.04, 95% CI 0.64 to 1.68)
or in people with a time-updated CD4 count under 50
cells/μL (HR 1.46, 95% CI 0.70 to 3.04).
TB risk was marginally higher in people who had started ART
less than 3 months ago (HR 1.36, 95% CI 0.98 to 1.89) but 56%
lower in people who started ART 3 or more months ago (HR 0.44,
95% CI 0.34 to 0.58).
Compared with people who had not begun ART, hazard ratios for
incident TB varied by age and by whether the latest CD4 count
was below 50:
• Under 35 years old: HR 0.67 (95% CI 0.38 to 1.18)
• 35 to 50 years old: HR 1.51 (95% CI 0.98 to 2.31)
• Over 50 years old: HR 3.20 (95% CI 1.34 to 7.60)
• CD4 count under 50: HR 2.30 (95% CI 1.03 to 5.14)
The HIV-CAUSAL team concludes that “combined ART reduced
tuberculosis incidence by half” in their cohort. But
“increases in tuberculosis incidence shortly after
combination ART, especially in those more than 50 years old
and those with CD4 cell counts below 50 cells/μL, suggested
unmasking immune reconstitution inflammatory
syndrome.”
Source: The
HIV-CAUSAL Collaboration. Impact of antiretroviral therapy on
tuberculosis incidence among HIV-positive patients in
high-income countries.
Clinical Infectious Disease. 2012; 54: 1364-1372.
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