1 mL of expectoration contains what number of TB bacilli in an active case of TB?
**Core Concept**
The question tests the understanding of the bacteriological load in a patient with active tuberculosis (TB), specifically the number of **Mycobacterium tuberculosis** bacilli present in the sputum. This knowledge is crucial for understanding the infectiousness of the patient and the risk of transmission to others. The presence of these bacilli is typically detected through sputum smear microscopy.
**Why the Correct Answer is Right**
In an active case of TB, the sputum can contain a significant number of **Mycobacterium tuberculosis** bacilli, making the patient infectious. The correct answer reflects the average bacteriological load that can be expected in such cases, which is around 1,000 to 10,000 bacilli per milliliter of sputum, but the exact number can vary.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it underestimates the bacteriological load typically found in active TB cases.
**Option B:** This option overestimates the typical load, although it's closer to the truth than option A.
**Option D:** This option significantly overestimates the number of bacilli, which is not characteristic of the average active TB case.
**Clinical Pearl / High-Yield Fact**
It's crucial to remember that even a small number of **Mycobacterium tuberculosis** bacilli can be infectious, especially in closed or poorly ventilated environments. The exact number can vary based on the stage of the disease, the presence of cavitation, and the effectiveness of the patient's cough mechanism.
**Correct Answer:** C. 1,000 to 10,000 bacilli.