Screening for TB infection is crucial to prevent progression to active TB disease.
TB screening in low incidence populations, i.e., the developed nations, is a critical public health service aimed at finding TB in an early latent phase when it is easily treatable. Routine, periodic screening is focused on the millions of people working in high exposure and risk environments such as health care and educational professionals, incarcerated individuals, the military, immigrant populations, food service personnel, nursing home residents, and the immunocompromised.
For these populations, TB infection is usually diagnosed, or “ruled-in” through combination and cross-reference between diagnostic tools, as well as subjective analysis of patient history, symptoms and environment. Current screening tools include the century old tuberculin skin test (TST) and blood-based interferon-gamma (IFN-γ) release assays (IGRA).
A confirming diagnosis can take 2-5 business days and requires multiple patient visits to multiple clinical locations. Beyond the trials of patient non-compliance and time/cost required to obtain a result, the current testing regime suffers from challenges in accuracy, sample handling requirements, laboratory availability, test antigen availability, and quality control. To date, new tests for TB screening have been slow to evolve, playing a distant second to global attention on the prevention, diagnosis and treatment of active and drug resistant TB disease.
If the diagnosis is positive for TB infection, clinical treatment of daily medication proceeds over 6-9 months. It is estimated that 30% of people prescribed antibiotics for treatment of TB infection do not have the infection at all, and that over 40% of patients that start treatment do not finish it. Both shortcomings lead to the unfortunate emergence of drug-resistant strains of TB, which are much more difficult and expensive to treat.