A 32-year-old woman from Delhi presents with a 10-day history of sustained fever, headache, and abdominal pain. Blood culture grows Salmonella typhi. Her roommate develops similar symptoms 5 days later with positive blood culture for Salmonella paratyphi B. Which feature best distinguishes typhoid fever caused by S. typhi from paratyphoid fever caused by S. paratyphi?

Explanation

## Distinguishing Typhoid from Paratyphoid Fever ### Clinical Presentation Comparison | Feature | Typhoid (S. typhi) | Paratyphoid (S. paratyphi) | |---------|-------------------|-------------------------| | **Incubation period** | 7–14 days (range: 6–30 days) | 1–3 days (shorter, more acute) | | **Onset** | Insidious, gradual | Often abrupt | | **Fever pattern** | Sustained, stepladder rise | Variable, may be remittent | | **Severity** | Generally more severe | Milder, shorter course | | **Rose spots** | Present in ~5–10% of cases | Rare, but can occur | | **GI symptoms** | Constipation early, diarrhea late | Diarrhea prominent early | | **Splenomegaly** | Common (75–80%) | Common (60–70%) | | **Hepatomegaly** | Common | Common | | **Complications** | Perforation (1–3%), myocarditis, encephalopathy | Perforation rare (<0.5%), milder complications | **Key Point:** The **shorter incubation period and more acute onset of paratyphoid fever** (1–3 days vs. 7–14 days for typhoid) is the most reliable clinical discriminator. Paratyphoid typically presents with sudden fever and prominent diarrhea, whereas typhoid has an insidious onset with early constipation. ### Why Other Features Are NOT Discriminatory **Rose spots:** Although classically associated with typhoid, they occur in only 5–10% of cases and are NOT pathognomonic—they can appear in paratyphoid as well. This is an unreliable discriminator. **Hepatosplenomegaly:** Both conditions cause splenomegaly and hepatomegaly with similar frequency. Paratyphoid does NOT present with hepatomegaly alone; both organs are commonly affected in both diseases. **Intestinal perforation:** While more common in typhoid (1–3% of cases), perforation can still occur in paratyphoid (rare but documented). It is not an exclusive feature of typhoid. **High-Yield:** In clinical exams, remember that **paratyphoid = acute onset + prominent diarrhea early**, whereas **typhoid = insidious onset + early constipation**. The incubation period difference is the most reliable discriminator. **Clinical Pearl:** Paratyphoid fever often mimics acute gastroenteritis due to its abrupt onset and diarrhea-predominant presentation, whereas typhoid's insidious onset with headache and sustained fever is more characteristic. [cite:Harrison 21e Ch 157]