How many consecutive negative sputum cultures indicate that a patient is noninfectious?

How many consecutive negative sputum cultures indicate that a patient is noninfectious?

• A. One
• B. Four
• C. None
• D. Two or three

Answer: (D)

In TB care, infectiousness is judged by whether viable Mycobacterium tuberculosis can still be cultured from sputum. Because a single negative culture can be unreliable due to sampling variation, clinicians look for multiple negatives on separate days. Two consecutive negative sputum cultures are typically taken as evidence that the patient is no longer contagious, and some guidelines require three for added certainty. So, two or three consecutive negative cultures indicate noninfectiousness. A lone negative culture isn’t sufficient to clearance, and asking for four is stricter than most protocols.

In TB care, infectiousness is judged by whether viable Mycobacterium tuberculosis can still be cultured from sputum. Because a single negative culture can be unreliable due to sampling variation, clinicians look for multiple negatives on separate days. Two consecutive negative sputum cultures are typically taken as evidence that the patient is no longer contagious, and some guidelines require three for added certainty. So, two or three consecutive negative cultures indicate noninfectiousness. A lone negative culture isn’t sufficient to clearance, and asking for four is stricter than most protocols.