Which statement best describes the contagion risk of smear-negative TB?

• A. It is lower than smear-positive but still transmissible
• B. It is higher than smear-positive
• C. It is not contagious
• D. It is equally contagious

Answer: (A)

Contagion risk in smear-negative TB depends on how many bacteria are being shed in the air. When the sputum smear is negative, there are fewer bacilli present, so the chance of transmitting the disease through coughing or aerosols is lower than with smear-positive TB. But the shedding is not zero—some bacilli can still be expelled and infected contacts can occur, especially with close or prolonged exposure. So smear-negative TB is less contagious than smear-positive TB, yet it remains transmissible.

That’s why the best description is that it is lower than smear-positive but still transmissible. The other options aren’t accurate because smear-negative TB can still spread disease (not noncontagious), its contagion isn’t as high as smear-positive (not equally contagious), and it isn’t zero (not zero contagious).