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Patient Story: Rahul, a 28-year-old software engineer, presents to the outpatient clinic with continuous high fever (103°F), headache, severe fatigue, and loss of appetite for 8 days. He notices his fever rises in a step-ladder pattern every evening. Physical Examination Findings: - Temperature: 102.8°F - Pulse: 76 beats per minute (Relative Bradycardia / Faget's sign — pulse is slower than expected for high fever) - Abdomen: Mild tenderness in the upper left quadrant with mild enlargement of the spleen (splenomegaly). Diagnostic Reasoning & Testing: The clinician suspects Enteric Fever (Typhoid fever caused by Salmonella Typhi). To confirm, a step-by-step diagnostic panel is ordered based on the illness duration: 1. Microbial Culture (Blood Culture): Since the patient is in the 2nd week of illness, 10 mL of blood is inoculated into a blood culture bottle (Brain Heart Infusion Broth). After 24 hours of incubation, subculture onto MacConkey Agar produces pale, translucent colonies (non-lactose fermenting gram-negative bacilli). 2. Antimicrobial Susceptibility Testing (AST): The cultured Salmonella Typhi is tested against antibiotics. It shows sensitivity to Ceftriaxone and Azithromycin, but resistance to Ciprofloxacin. 3. Serology (Widal Test): Serum agglutination test shows high antibody titers: Anti-O titer is 1:320 (cut-off > 1:160) and Anti-H titer is 1:320, confirming active Salmonella infection. 4. Molecular Test (Multiplex PCR): PCR performed on blood targeting the flagellin gene (fliC) confirms Salmonella enterica serovar Typhi DNA within 4 hours. Management Plan: Rahul is started on Injection Ceftriaxone 2 grams IV daily for 10 days based on the culture sensitivity report. His fever completely resolves on Day 4 of treatment, and he recovers fully.