American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the most reliable method for diagnosing typhoid fever?

1. Isolating the organism from blood, stool, urine, or bone marrow

2. Serum sputum culture

3. Skin biopsy

4. Urine dipstick test

The correct answer is: Isolating the organism from blood, stool, urine, or bone marrow

Isolating the organism from blood, stool, urine, or bone marrow is recognized as the most reliable method for diagnosing typhoid fever. The causative agent of typhoid fever is *Salmonella enterica* serotype Typhi, and finding this bacterium in body fluids confirms the diagnosis. Blood cultures are particularly important because they allow for the identification of the bacteria during the fever phase when it is actively circulating in the bloodstream. Stool cultures can also be useful, especially after the initial fever subsides. Bone marrow cultures are also a very sensitive method, although they are less commonly performed due to the invasive nature of the procedure. Collectively, these methods provide direct evidence of the infection and can help determine the antibiotic susceptibility of the organism. In contrast, other options listed do not offer reliable means of diagnosing typhoid fever. Serum sputum cultures are not standard for this condition, as typhoid primarily affects the gastrointestinal system rather than the respiratory tract. Skin biopsy is used for diagnosing skin conditions or systemic diseases but does not pertain to typhoid fever. A urine dipstick test lacks specificity for typhoid and is typically not used for diagnosing this illness, as it primarily detects the presence of blood, glucose,