# Enteric Fever and Salmonella Typhi

> Enteric fever and Salmonella Typhi for NEET-PG Microbiology, covering pathogenesis, bone marrow culture, chronic carriers, rose spots and treatment choices.

- Canonical URL: https://prepelephant.com/topics/neet-pg/microbiology/enteric-fever-salmonella-typhi
- Exam / course: NEET-PG · Subject: Microbiology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-14
- Last updated: 2026-10-14
- Reference basis: Harrison's Principles of Internal Medicine; Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases; Ananthanarayan and Paniker's Textbook of Microbiology
- How to cite: "Enteric Fever and Salmonella Typhi", PrepElephant, https://prepelephant.com/topics/neet-pg/microbiology/enteric-fever-salmonella-typhi

## Direct answer

Enteric fever is a systemic infection caused by Salmonella Typhi and, less often, by Salmonella Paratyphi A, B or C, in which bacteria reach the bloodstream through Peyer's patches and the reticuloendothelial system. Its hallmarks are prolonged fever, relative bradycardia and rose spots, and culture of blood or bone marrow provides the definitive diagnosis. Azithromycin or ceftriaxone is commonly used, with the choice guided by local resistance patterns.

## What you must remember

- **Organism:** a Gram-negative, motile, non-lactose-fermenting Salmonella with a Vi capsular antigen, and humans are its only natural host.
- **Pathogenesis:** bacteria are taken up through M cells over Peyer's patches, causing primary bacteraemia in the first week and secondary bacteraemia from the reticuloendothelial system later.
- **Relative bradycardia:** a pulse rate lower than expected for the degree of fever, known as Faget sign.
- **Rose spots:** faint salmon-coloured macules on the abdomen and chest, seen in a minority of patients.
- **Culture yield:** blood culture is most useful in the first week, and bone marrow culture remains the most sensitive, even after antibiotics have started.
- **Chronic carriage:** excretion beyond one year, usually from the gall bladder, and often associated with gallstones.
- **Resistance:** multidrug resistance and reduced fluoroquinolone susceptibility, linked to gyrA mutations, are widespread in the region.
- **Vaccines:** Vi polysaccharide, live oral Ty21a and Vi conjugate vaccines are available.

## A diagnostic and treatment pathway for suspected enteric fever

A 20-year-old student has a week of rising fever, headache, abdominal discomfort and relative bradycardia. The steps show how cultures, complications and empirical therapy are sequenced.

1. **Take cultures before antibiotics:** blood culture in the first week and bone marrow culture give the highest yield, so samples should be drawn before antibiotics start.
2. **Use serology only as support:** Widal or Typhidot results are interpreted cautiously, since they are less sensitive and can remain positive after past exposure.
3. **Look for complications:** intestinal perforation, haemorrhage, encephalopathy and myocarditis need urgent surgical or intensive care review.
4. **Test susceptibility:** isolates are tested against ampicillin, cotrimoxazole, chloramphenicol, fluoroquinolones and third-generation cephalosporins, because resistance patterns vary.
5. **Choose empirical therapy by local resistance:** azithromycin or ceftriaxone is commonly used, and fluoroquinolones are chosen only when the isolate is susceptible.
6. **Plan duration and follow-up:** courses vary by drug and severity, and persistent carriage is checked with stool or urine culture after treatment.

## Where the exam tries to catch you

Enteric fever questions test which sample to send, which test is supportive, and what defines a carrier.

- **Trap:** relying on blood culture alone after antibiotics have started — **Correct:** bone marrow culture keeps its yield even after treatment has begun, because bacteria persist in marrow.
- **Trap:** assuming a stool culture is the best early test — **Correct:** stool and urine cultures become positive later in the illness, while blood culture is best in the first week.
- **Trap:** believing every Typhi carrier is symptomatic — **Correct:** chronic carriers are usually asymptomatic, with the gall bladder as the reservoir, and cholecystectomy is considered in selected cases.

## Frequently asked questions

### Why is bone marrow culture the most sensitive test for Salmonella Typhi?
Bone marrow culture is the most sensitive test for enteric fever because Salmonella Typhi persists in the reticuloendothelial system, including bone marrow, for longer than in blood. Its yield remains high even after antibiotic therapy has started.

### What is relative bradycardia in enteric fever?
Relative bradycardia is a pulse rate lower than expected for the degree of fever, and it is a classic clinical sign of typhoid. It is also called Faget sign and is useful in the bedside assessment of fever.

### How is a Salmonella Typhi carrier identified?
A carrier is identified by persistent excretion of Salmonella Typhi in stool or urine beyond one year after infection, usually with gall bladder carriage. Culture and anti-Vi antibody testing help identify carriers during epidemiological screening.

### Why do rose spots occur in enteric fever?
Rose spots are faint salmon-coloured macules on the abdomen and chest, believed to reflect bacterial emboli in skin capillaries during bacteraemia. They appear in a minority of patients and are a supportive clinical feature rather than a diagnostic one.

### Which vaccines protect against enteric fever?
The Vi polysaccharide vaccine, the live oral Ty21a vaccine and Vi conjugate vaccines protect against Salmonella Typhi. Conjugate vaccines are generally preferred for young children because they induce a stronger and more durable immune response.