## Distinguishing Feature: Transmissibility **Key Point:** The critical epidemiological distinction between PTB and EPTB is the mode and efficiency of transmission. ### Transmission Dynamics | Feature | Pulmonary TB | Extrapulmonary TB | |---------|--------------|-------------------| | **Airborne transmission** | Yes (droplet nuclei) | No (non-infectious) | | **Public health threat** | High (community spread) | Low (individual disease) | | **Infectiousness** | Depends on cavity status & bacillary load | Non-infectious to others | | **AFB in secretions** | Present in sputum/respiratory secretions | Absent or minimal | **High-Yield:** PTB is the only form of TB that poses a significant transmission risk to the general population. EPTB (lymph node TB, spinal TB, TB meningitis, etc.) does not transmit from person to person, making it an epidemiological dead-end [cite:Park 26e Ch 7]. ### Why Transmissibility Matters 1. **Case detection strategy:** TB control programs prioritize identification and treatment of PTB cases because each untreated case can infect 10–15 contacts annually. 2. **Contact tracing:** Only PTB patients require systematic contact investigation. 3. **Infection control:** Airborne precautions apply only to PTB; EPTB does not require respiratory isolation. **Clinical Pearl:** A patient with spinal TB (Pott's disease) or TB meningitis poses NO transmission risk to healthcare workers or family members, even if untreated. This is why EPTB is not counted in TB incidence for epidemiological surveillance in some contexts. ### Mnemonic **"PTB = Transmission; EPTB = Termination"** — PTB continues the chain of transmission; EPTB ends it.
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