Temporal trends in the prevalence of Mycobacterium tuberculosis infection in South African adolescents

<sec id="st1"> <title>SETTING</title> South Africa. </sec> <sec id="st2"> <title>OBJECTIVE</title> 1) To measure changes in the adolescent prevalence of latent tuberculous infection (LTBI) between 2005 and 2015, and 2) to evaluate medium-term impact of TB control measures on LTBI prevalence. </sec> <sec id="st3"> <title>DESIGN</title> We compared baseline data from a cohort study (2005-2007) and a vaccine trial (2014-2015) which enrolled adolescents from the same eight South African high schools. LTBI was defined based on QuantiFERON^®-TB Gold In-Tube test positivity. </sec> <sec id="st4"> <title>RESULTS</title> We analysed data from 4880 adolescents between 2005 and 2007, and 1968 adolescents between 2014 and 2015, when the average LTBI prevalence was respectively 43.8% (95%CI 28.4-59.1) vs. 48.5% (95%CI 41.1-55.8). Age-specific LTBI prevalence increased between the ages 12 and 18 years by 13% only in lower socio-economic quintile schools, where the average LTBI prevalence was unchanged between the two periods (54% vs. 53%). In the highest socio-economic quintile schools, LTBI prevalence did not increase with age; however, the average LTBI prevalence increased from 20% to 38% between the two periods. </sec> <sec id="st5"> <title>CONCLUSION</title> Adolescent LTBI prevalence remained high and constant over a decade, suggesting that Mycobacterium tuberculosis transmission to children was not impacted in the medium term by effective TB control efforts. Trends in adolescent LTBI prevalence should be interpreted in the context of the sociodemographic factors that affect the risk of transmission before and during adolescence. </sec>.

Impact of isoniazid preventive therapy on the evaluation of long-term effectiveness of infant MVA85A vaccination

SETTING:

South Africa.

OBJECTIVE:

To evaluate the long-term effectiveness of infant modified vaccinia Ankara virus-expressing antigen 85A (MVA85A) vaccination against tuberculosis (TB).

DESIGN:

We analysed data from a double-blind randomised placebo-controlled Phase 2b MVA85A infant TB vaccine trial (2009–2012), with extended post-trial follow-up (2012–2014). Isoniazid preventive therapy (IPT) was provided by public health services according to national guidelines. The primary outcome was curative treatment for TB disease. Survival analysis and Poisson regression were used for study analysis.

RESULTS:

Total follow-up was 10 351 person-years of observation (pyo). Median follow-up age was 4.8 years (interquartile range 4.4–5.2). There were 328 (12%) TB cases. TB disease incidence was 3.2/100 pyo (95%CI 2.8–3.5) overall, and respectively 3.3 (95%CI 2.9–3.9) and 3.0 (95%CI 2.6–3.5)/100 pyo in the MVA85A vaccine and placebo arms. A total of 304 children (11%) received IPT, with respectively 880 and 9471 pyo among IPT and non-IPT recipients. There were 23 (7.6%) TB cases among 304 IPT recipients vs. 305 (12.9%) among 2374 non-IPT recipients (P = 0.008). IPT effectiveness was 85% (95%CI 76–91).

CONCLUSION:

Extended follow-up confirms no long-term effectiveness of infant MVA85A vaccination, but a six-fold reduction in TB risk can be attributed to IPT. National TB programmes in high TB burden countries should ensure optimal implementation of IPT for eligible children.