Tuberculosis screening in high human immunodeficiency virus prevalence settings: turning promise into reality

Abstract

Twenty years of sky-high tuberculosis (TB) incidence rates and high TB mortality in high human immunodeficiency virus (HIV) prevalence countries have so far not been matched by the same magnitude or breadth of responses as seen in malaria or HIV programmes. Instead, recommendations have been narrowly focused on people presenting to health facilities for investigation of TB symptoms, or for HIV testing and care. However, despite the recent major investment and scale-up of TB and HIV services, undiagnosed TB remains highly prevalent at community level, implying that diagnosis of TB remains slow and incomplete. This maintains high transmission rates and exposes people living with HIV to high rates of morbidity and mortality. More intensive use of TB screening, with broader definitions of target populations, expanded indications for screening both inside and outside of health facilities, and appropriate selection of new diagnostic tools, offers the prospect of rapidly improving population-level control of TB. Diagnostic accuracy of suitable (high throughput) algorithms remains the major barrier to realising this goal. In the present study, we review the evidence available to guide expanded TB screening in HIV-prevalent settings, ideally through combined TB-HIV interventions that provide screening for both TB and HIV, and maximise entry to HIV and TB care and prevention. Ideally, we would systematically test, treat and prevent TB and HIV comprehensively, offering both TB and HIV screening to all health facility attendees, TB households and all adults in the highest risk communities. However, we are still held back by inadequate diagnostics, financing and paucity of population-impact data. Relevant contemporary research showing the high need for potential gains, and pitfalls from expanded and intensified TB screening in high HIV prevalence settings are discussed in this review.

Figure 1

Patient flow and main entry points into TB screening. HIV entry points (5 and 6) are considered separately from other targeted risk groups, such as household contacts (4). TB screening can be directed against subclinical TB or at early stages of health seeking. TB = tuberculosis; HIV = human immunodeficiency virus; HCW = health care worker.

Figure 2

TB progression along an individual patient pathway. Depending on the nature of TB screening, individuals can be targeted at any point along their disease progression. This will influence the choice of diagnostic tools and the principal aim of screening. TB = tuberculosis; MDR-TB = multidrug-resistant TB; PLHIV = people living with HIV; NAAT = nucleic acid amplification test; HIV = human immunodeficiency virus; ART = antiretroviral therapy; IPT = isoniazid preventive therapy; CPT = cotrimoxazole preventive therapy.

Figure 3

Possible patterns of disease progression and onset of infectiousness. TB screening gains in terms of secondary infections averted and ease of diagnosis (sensitivity of diagnostic tools) will depend on the pattern of onset of infectiousness relative to symptoms, and how the screen is targeted. Screening may detect patients who are in the process of self cure following transient culture positivity. Adapted from Dowdy et al. TB = tuberculosis.