## TB Incidence vs. Prevalence Relationship **Key Point:** In high-burden TB countries, prevalence exceeds incidence because of prolonged disease duration (months to years if untreated) and incomplete case detection, creating a reservoir of undiagnosed and inadequately treated cases. **High-Yield:** The relationship is governed by the epidemiological principle: $$\text{Prevalence} \approx \text{Incidence} \times \text{Duration of Disease}$$ In India, WHO estimates show: - **Incidence:** ~199 per 100,000 population - **Prevalence:** ~244 per 100,000 population (higher due to long disease duration and diagnostic delays) **Clinical Pearl:** This gap between incidence and prevalence is a key indicator of health system performance. Countries with robust TB programs (high case detection, rapid treatment initiation) show lower prevalence relative to incidence because cases are removed from the pool quickly. ## Why Prevalence > Incidence in High-Burden Settings | Factor | Impact on Prevalence | |--------|---------------------| | Long disease duration (months–years untreated) | Accumulates cases in population | | Low case detection rate (<70% in many regions) | Undiagnosed cases remain in prevalence pool | | Treatment delays and loss to follow-up | Extends duration of active disease | | High relapse rates | Adds previously treated cases back | **Mnemonic:** **DUPE** = Duration, Undetected, Prolonged, Excess - **D**uration of disease is long - **U**ndetected cases accumulate - **P**rolonged treatment delays - **E**xcessive prevalence relative to incidence
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