The infectivity of a patient with diphtheria is –
**Core Concept**
The underlying principle being tested is the understanding of the infectious period of diphtheria, a bacterial infection caused by *Corynebacterium diphtheriae*. The infectivity of a patient depends on the presence and virulence of the bacteria.
**Why the Correct Answer is Right**
The correct answer choice is related to the duration the patient remains contagious, which is typically until 2 weeks after the onset of illness or until 2 negative throat cultures are obtained after antibiotic treatment. This is because *Corynebacterium diphtheriae* can be transmitted through respiratory droplets.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it underestimates the duration of infectivity.
**Option B:** This option overestimates the duration of infectivity.
**Option D:** This option does not accurately reflect the infectivity period.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that patients with diphtheria should be isolated to prevent spread, and antibiotic treatment should be initiated promptly to reduce infectivity.
**Correct Answer:** D. 2 weeks or until 2 negative throat cultures after antibiotic treatment.