**Core Concept:**
Salmonella is a type of bacteria that can cause infections in humans, particularly salmonellosis. The incubation period (time from infection to onset of symptoms) for salmonella infections is typically around 12-72 hours. Once the symptoms appear, the infected individual becomes contagious and can transmit the infection to others until they are treated and cured.

**Why the Correct Answer is Right:**
The correct answer, C. till symptoms disappear, is the period during which the infected person is contagious. Salmonella infections cause symptoms such as fever, abdominal pain, and diarrhea, which indicate the presence of the bacteria in the infected individual. Until these symptoms disappear, the person remains a potential source for spreading the infection to others.

**Why Each Wrong Option is Incorrect:**
A. 14 days: This is too long, as the person becomes non-contagious much sooner after starting antibiotic treatment or when their symptoms improve.
B. 14 days post-infection: This is also incorrect, as the incubation period is shorter than 14 days, and the person remains contagious even before the onset of symptoms.
D. till antibiotic therapy is completed: Antibiotic therapy may reduce the duration of contagiousness but does not guarantee the individual is no longer contagious. Contagiousness depends on the presence of symptoms rather than the completion of antibiotic treatment.

**Clinical Pearl / High-Yield Fact:**
In salmonella infections, the period of isolation should be based on symptom resolution rather than arbitrary timeframes like 14 days or completion of antibiotic therapy. Isolation should be continued until the infected individual is no longer contagious, which is typically when their symptoms have disappeared. This ensures that the individual no longer poses a risk of transmitting the infection to others.