**Core Concept**
Typhoid fever is a systemic infection caused by Salmonella Typhi, requiring a definitive diagnosis to initiate appropriate treatment. The definitive diagnosis involves identifying the causative organism, either through direct culture or molecular detection.

**Why the Correct Answer is Right**
The most dependable definitive diagnosis of typhoid fever is by **Widal test-negative blood culture**. Blood culture is a direct method of detecting the pathogen, allowing for its isolation and identification. This method has a high sensitivity, especially during the second week of illness. It is considered the gold standard for diagnosing typhoid fever.

**Why Each Wrong Option is Incorrect**
**Option A:** Serological tests, such as the Widal test, are not definitive as they detect antibodies against the O and H antigens, which can be present in healthy carriers or individuals with past exposure.

**Option B:** Urine culture may be positive in some cases of typhoid fever but is not as reliable as blood culture for definitive diagnosis.

**Option C:** Stool culture can be positive in typhoid fever but is less sensitive than blood culture for detecting the pathogen.

**Clinical Pearl / High-Yield Fact**
In cases of suspected typhoid fever, multiple blood cultures should be collected over 24-48 hours to increase the likelihood of isolation of the pathogen.

**Correct Answer: C. Stool culture may be positive in typhoid fever but is less sensitive than blood culture for detecting the pathogen.**