Enteric fever

By the end of this study note, the student will be able to evaluate, diagnose, and outline the initial and definitive management of enteric fever in the Kenyan setting; drug doses and institutional protocols must be verified against current Kenya Ministry of Health guidelines and local hospital formularies.

Definition

Enteric fever is a systemic, life-threatening infection caused by the invasive, host-restricted bacteria Salmonella enterica serovar Typhi (S. Typhi) and Salmonella enterica serovars Paratyphi A, B, and C. It is characterized by persistent bacteremia, prolonged step-ladder fever, intracellular replication within the reticuloendothelial system, and hyperplasia and ulceration of intestinal lymphoid tissue (Peyer's patches).

Anatomy and physiology you need

• Peyer’s patches (Terminal ileum): Aggregated lymphoid follicles located in the submucosa and lamina propria of the ileum, covered by specialized microfold cells (M-cells). M-cells lack microvilli and sample luminal antigens, serving as the entry portal for Salmonella into gut-associated lymphoid tissue (GALT).
• Mononuclear phagocyte system (Reticuloendothelial system): Macrophages and histiocytes residing within mesenteric lymph nodes, liver (Kupffer cells), spleen, and bone marrow. These cells phagocytose the bacteria but fail to eradicate them, serving as the primary site for intracellular bacterial replication.
• Biliary tract and gallbladder: The alkaline, bile-rich environment promotes S. Typhi colonization and biofilm formation, particularly in the presence of gallstones. Chronic biliary excretion provides a continuous reservoir for asymptomatic fecal shedding and transmission.
• Gastric acid barrier: Normal gastric acidity (pH < 2.0) acts as the primary chemical barrier that destroys ingested enteric pathogens before they reach the small intestine.

Causes and risk factors

Etiological agents

• Salmonella enterica subspecies enterica serovar Typhi (predominant cause of severe systemic disease).
• Salmonella enterica subspecies enterica serovars Paratyphi A, B, and C (often causes a clinically indistinguishable but generally milder illness; Paratyphi A incidence is rising globally).

Transmission

• Fecal-oral route via direct ingestion of water or food contaminated by human feces or urine from acute cases or chronic carriers (human-only reservoir).

Local and tropical risk factors (Kenyan context)

Pathophysiology

Ingestion of contaminated food or water $\downarrow$ Survival through gastric acid barrier $\downarrow$ Adhesion to and invasion of terminal ileum mucosa via M-cells of Peyer’s patches $\downarrow$ Uptake by subepithelial macrophages and dendritic cells in lamina propria $\downarrow$ Inhibition of phagolysosome fusion and survival via Salmonella Pathogenicity Islands (SPI-1, SPI-2) and Vi capsule $\downarrow$ Drainage via lymphatics to mesenteric lymph nodes $\downarrow$ Primary transient bacteremia (asymptomatic incubation period: 7–14 days) $\downarrow$ Dissemination and intracellular replication within reticuloendothelial organs (liver, spleen, bone marrow) $\downarrow$ Secondary sustained bacteremia with high bacterial loads (onset of clinical step-ladder fever and constitutional symptoms) $\downarrow$ Pyrogen release (TNF-alpha, IL-1, IL-6) from infected macrophages causing systemic inflammatory response and relative bradycardia $\downarrow$ Re-invasion of the gallbladder with subsequent high-concentration excretion into bile $\downarrow$ Re-entry of bile-borne bacteria into the lumen of the small bowel $\downarrow$ Hyper-sensitized Peyer's patches undergo severe mononuclear cell infiltration and marked hypertrophy $\downarrow$ Ischemic necrosis of lymphoid follicles leading to mucosal sloughing, oval ulcer formation, and potential hemorrhage or free perforation

Clinical features

History questions that matter

• Fever pattern and duration: Ask about a step-ladder rise over several days versus sudden onset; untreated enteric fever classically climbs over the first week to a sustained high plateau.
• Gastrointestinal symptoms: Ask whether the patient has constipation (classic in early adult disease due to intestinal hypomotility) or diarrhea ("pea-soup", more frequent in children, advanced disease, and immunocompromised hosts).
• Neurological features: Ask about persistent dull frontal headache, apathy, insomnia, or confusion ("typhoid state").
• Exposure risks: Inquire about untreated drinking water, street food vending, poor sanitation, and travel from informal urban settlements or rural endemic zones.
• Prior antibiotic exposure: Many Kenyan patients self-medicate with over-the-counter ampicillin, cotrimoxazole, or ciprofloxacin, blunting the clinical presentation and causing negative blood cultures.
• Underlying conditions: Establish HIV status, sickle cell disease, or malaria co-infection, which worsen disease course or predispose to invasive salmonellosis.

Examination findings and why each occurs

• Fever with relative bradycardia (Faget sign): High core temperature without the expected physiological pulse rise. Caused by direct myocardial toxicity from bacterial endotoxins, vagal tone stimulation, or impaired sinoatrial node response.
• Coated tongue: Thick white or brown furring over the dorsum with red, clean margins and tip, reflecting systemic toxicity and dehydration.
• Abdominal findings:
  • Right lower quadrant tenderness: Inflammation of terminal ileal Peyer's patches and mesenteric lymphadenitis.
  • Abdominal distension and borborygmi: Paralytic ileus induced by local intestinal wall inflammation and neurotoxins.
  • Guarding or rigidity: Indicates micro-perforation or overt peritonitis of the thin, inflamed ileum.
• Hepatosplenomegaly: Soft, mildly tender enlargement resulting from massive reticuloendothelial uptake and macrophage hyperplasia handling the intracellular bacteria.
• Rose spots: Faint, blanching, salmon-pink maculopapular lesions (2–4 mm) clustered on the trunk. Caused by bacterial embolization into the dermis; frequently missed in dark-skinned patients unless searched for under good natural light.
• "Coma vigil" / Typhoid state: Marked apathy, delirium, picking at bedclothes, and stupor seen in the second to third week, driven by systemic endotoxemia and neuroinflammation.

Differential diagnosis

Investigations

Diagnosis and severity

Establishing the diagnosis

A definitive diagnosis requires the isolation of Salmonella enterica serovar Typhi or Paratyphi from blood, bone marrow, stool, or urine. In resource-limited settings where cultures are delayed or unavailable, a probable diagnosis is made based on prolonged unexplained fever (≥3 days), abdominal symptoms, toxemia, leukopenia, and failure to respond to antimalarials, supported by local epidemiology.

Severity stratification

• Uncomplicated enteric fever: Patient is fully conscious, able to take oral medications and fluids, shows no peritoneal signs, and maintains normal vital signs aside from fever.
• Complicated / Severe enteric fever: Defined by the presence of any of the following:
  • Gastrointestinal: Intestinal perforation (peritonitis, shock) or severe lower intestinal hemorrhage (melena or hematochezia with acute drop in hemoglobin).
  • Neurological: Delirium, obtundation, coma, or generalized seizures (typhoid encephalopathy).
  • Cardiopulmonary: Myocarditis (arrhythmias, heart failure) or pneumonia.
  • Hemodynamic: Septic shock (hypotension, prolonged capillary refill, cool extremities, oliguria) requiring resuscitation and intensive monitoring.

Management

Immediate Stabilisation

The immediate priority is to address haemodynamic instability and severe dehydration.

• Fluid Resuscitation: Intravenous fluids are crucial for hypovolemic shock. Use crystalloids (e.g., Normal Saline, Ringer's Lactate) to restore circulating volume. Monitor urine output and vital signs closely.
• Electrolyte Correction: Correct significant electrolyte imbalances, especially hyponatremia or hypokalemia, guided by laboratory results.
• Antipyretics: Paracetamol can be used for fever control to improve patient comfort and reduce metabolic demand.

Definitive Treatment

Antibiotics are the cornerstone of definitive management.

• Choice of Antibiotics:
  • First-line: Ceftriaxone is often the preferred empirical choice due to its broad spectrum, efficacy, and favourable safety profile. It penetrates well into the central nervous system.
  • Alternatives: Other options include fluoroquinolones (e.g., Ciprofloxacin) or azithromycin. The choice may be influenced by local resistance patterns, patient allergies, and severity of illness.
  • Oral Therapy: Once the patient is afebrile and clinically improving, and if oral intake is tolerated, a switch to oral antibiotics (e.g., azithromycin or a fluoroquinolone) may be considered for a full course.
• Duration of Treatment: A typical course lasts for 10-14 days, but this can be extended in complicated cases or if there is a poor clinical response.
• Steroids: Corticosteroids (e.g., Dexamethasone) may be considered in patients with severe enteric fever and signs of increased intracranial pressure or shock, but their routine use is debated and should be carefully considered.

Monitoring and Follow-up

Close monitoring is essential to assess treatment response and detect complications.

• Clinical Assessment: Daily assessment of fever, vital signs, hydration status, abdominal examination, and neurological status.
• Laboratory Monitoring: Repeat blood counts and electrolytes as clinically indicated. Blood cultures should be repeated if there is a lack of clinical improvement.
• Follow-up: Patients should be advised on hygiene practices to prevent further transmission. Stool cultures may be considered after treatment to ensure eradication, especially in healthcare workers or food handlers.

Contraindications and Safety

• Antibiotic Allergies: Documented allergies to specific antibiotic classes require careful selection of alternatives.
• Renal or Hepatic Impairment: Dose adjustments may be necessary for certain antibiotics.
• Pregnancy and Lactation: Antibiotic choice needs careful consideration.
• Fluoroquinolone Use: Avoid in children due to potential cartilage damage.

Complications and Prognosis

Enteric fever can lead to significant morbidity and mortality if not managed promptly and effectively.

Prognosis: With prompt diagnosis and appropriate antibiotic therapy, the prognosis is generally good. However, complications significantly worsen the prognosis and increase mortality. Untreated or delayed treatment carries a high mortality rate. Chronic carrier state can occur, particularly in individuals with gallstones.

High-yield Exam Points

• Look-alike Conditions: Typhoid fever often mimics malaria, tuberculosis, amoebic dysentery, and other febrile illnesses. Differentiating features are key.
• Commonest Wrong First Steps: Starting antimalarials without confirming malaria, or delaying antibiotics while awaiting definitive stool or blood culture results in a severely ill patient.
• Examiner at Bedside:
  • "What is your primary concern with this patient?" (Dehydration, shock, perforation, neurological compromise).
  • "What are the key findings on examination that support your diagnosis?" (Relative bradycardia, rose spots, hepatosplenomegaly, abdominal tenderness).
  • "What are your immediate management priorities?" (Fluid resuscitation, antibiotics).
  • "How would you monitor this patient's response to treatment?" (Fever pattern, vital signs, urine output, abdominal exam).
  • "What are the potential complications you are looking out for?"

Clinical Case

A 10-year-old boy presents with a 7-day history of progressively worsening fever, headache, and abdominal pain. He has also developed a dry cough and is becoming increasingly lethargic. On examination, he is febrile (39.5°C), tachycardic, and has a blood pressure of 90/60 mmHg. His abdomen is distended and tender, particularly in the right iliac fossa. He has a few faint, pink, macular spots on his trunk.

Questions:

1. What is the most likely diagnosis, and what are the key findings supporting it?
2. What are your immediate management steps?
3. What are the most critical complications you need to monitor for in this child?

Model Answers:

1. The most likely diagnosis is enteric fever (typhoid fever). Key supporting findings include the prolonged fever, headache, abdominal pain, lethargy, relative bradycardia (implied by fever and lethargy), rose spots, and tenderness in the right iliac fossa (suggestive of ileal involvement).
2. Immediate management involves aggressive intravenous fluid resuscitation to address dehydration and potential shock, followed by prompt administration of intravenous antibiotics (e.g., Ceftriaxone). Close monitoring of vital signs and urine output is crucial.
3. The most critical complications to monitor for are intestinal perforation (indicated by worsening abdominal pain, rigidity, and signs of peritonitis), severe dehydration and shock, and neurological complications such as meningoencephalitis.

Practice Questions

Question 1

A 15-year-old boy presents with a 10-day history of high fever, headache, and abdominal discomfort. He has been treated for malaria empirically for the past 3 days with no improvement. On examination, he is febrile (39°C), lethargic, and has a palpable spleen tip. His pulse is 90 bpm, and his blood pressure is 100/70 mmHg. He has a few faint maculopapular lesions on his abdomen.

What is the most appropriate next step in management?

A. Repeat malaria smear and start artemisinin-based combination therapy. B. Start intravenous Ceftriaxone and obtain blood cultures. C. Perform an abdominal ultrasound to rule out appendicitis. D. Administer oral Paracetamol for fever control and observe.

Answer: B. Start intravenous Ceftriaxone and obtain blood cultures. Explanation: The prolonged fever despite antimalarial treatment, presence of rose spots, and lethargy strongly suggest enteric fever. Blood cultures are essential for diagnosis, and prompt antibiotic therapy is indicated.

Question 2

A 25-year-old woman with a known history of HIV infection presents with a 2-week history of intermittent fever, weight loss, and generalised abdominal pain. She has a dry cough and is increasingly weak. On examination, she is febrile (38.8°C), tachycardic, and hypotensive. Her abdomen is distended and diffusely tender.

Which of the following investigations is most crucial for establishing a diagnosis in this patient?

A. Sputum microscopy for Acid-Fast Bacilli. B. Stool microscopy for ova and parasites. C. Blood culture for Salmonella Typhi. D. HIV viral load and CD4 count.

Answer: C. Blood culture for Salmonella Typhi. Explanation: While HIV and TB are important co-morbidities, the clinical presentation with prolonged fever, abdominal pain, and potential for shock in the context of enteric fever makes blood culture for Salmonella Typhi the most critical investigation for the primary diagnosis.

Question 3

A 40-year-old man with a history of sickle cell disease presents with a 5-day history of fever, chills, and severe abdominal pain. He appears unwell and is dehydrated. On examination, his temperature is 39°C, pulse is 110 bpm, and blood pressure is 95/65 mmHg. His abdomen is tender, particularly in the right upper quadrant.

Why might this patient be at increased risk for a specific complication of enteric fever?

A. Increased risk of intestinal perforation due to vasculitis. B. Increased risk of cholecystitis and splenic abscess due to impaired splenic function. C. Increased risk of neurological complications due to underlying anaemia. D. Increased risk of haemolytic crisis due to antibiotic side effects.

Answer: B. Increased risk of cholecystitis and splenic abscess due to impaired splenic function. Explanation: Patients with sickle cell disease have impaired splenic function (functional asplenia), making them more susceptible to encapsulated organisms and complications like cholecystitis and splenic abscesses, which can be seen in enteric fever.

Question 4

Which of the following findings in a patient with suspected enteric fever would most strongly suggest intestinal perforation?

A. Relative bradycardia. B. Rose spots on the trunk. C. Rebound tenderness and guarding on abdominal examination. D. Hepatosplenomegaly.

Answer: C. Rebound tenderness and guarding on abdominal examination. Explanation: Rebound tenderness and guarding are classic signs of peritonitis, which is highly suggestive of intestinal perforation. Relative bradycardia and rose spots are typical of uncomplicated enteric fever.

Question 5

A patient with enteric fever is being treated with oral azithromycin. Which of the following is a contraindication to using fluoroquinolones as an alternative or subsequent therapy in this patient?

A. History of allergic reaction to penicillin. B. Age less than 18 years. C. Presence of gallstones. D. Mild renal impairment.

Answer: B. Age less than 18 years. Explanation: Fluoroquinolones are generally avoided in children and adolescents due to the risk of arthropathy (joint problems) and cartilage damage.

Drafted with AI assistance from standard references and reviewed for structure. Check details against your lecture notes and the Kenya MoH guideline.