Typhoid Fever

Overview
Pathogen Biology
Transmission & Epidemiology
Symptoms by Phase
Diagnosis
Treatment
Home & Supportive Care
Complications
Prevention & Vaccines
Key Research Papers
Connections
Featured Videos

1. Overview

Typhoid fever (also called enteric fever) is a systemic bacterial infection caused by Salmonella enterica serotype Typhi. An estimated 11–21 million cases occur globally each year, resulting in approximately 128,000–161,000 deaths. Paratyphoid fever, caused by S. Paratyphi A, B, or C, causes a clinically similar but typically milder illness.

Typhoid is a disease of contaminated food and water in settings with inadequate sanitation. It is one of the most important bacterial causes of fever in returning travelers from South Asia, sub-Saharan Africa, and Southeast Asia. The illness is characterized by sustained high fever, abdominal pain, relative bradycardia, splenomegaly, and a distinctive rash called "rose spots." Untreated, mortality reaches 10–30%; with appropriate antibiotic therapy, case fatality falls below 1%.

The emergence of extensively drug-resistant (XDR) typhoid — particularly a clone originating in Pakistan and spreading internationally — has complicated treatment, making vaccination increasingly important as a public health tool.

2. Pathogen Biology

Salmonella enterica serotype Typhi is a Gram-negative, facultative anaerobic, non-spore-forming rod in the family Enterobacteriaceae. It is a human-restricted pathogen — humans are the only reservoir and primary host.

Virulence Mechanisms

After ingestion, S. Typhi transits the stomach and enters the small intestine. The organism invades intestinal epithelium via M cells overlying Peyer's patches and is taken up by macrophages. Rather than being killed, S. Typhi survives and multiplies within mononuclear phagocytes using a type III secretion system (T3SS, encoded on Salmonella Pathogenicity Island 1 and 2) that injects bacterial effector proteins into host cells to subvert phagolysosome fusion and innate immune signaling.

A unique virulence feature of S. Typhi is the Vi (virulence) polysaccharide capsule, which inhibits complement deposition and phagocytosis and is the basis for the Vi polysaccharide vaccine. After an incubation period of 7–21 days (typically 10–14 days), bacteria re-enter the bloodstream from mesenteric lymph nodes in a primary bacteremia. Secondary bacteremia seeds the liver, gallbladder, spleen, bone marrow, and intestinal lymphoid tissue (Peyer's patches), causing the systemic illness.

Chronic Carriage

Approximately 1–5% of patients become chronic carriers — individuals who continue to shed S. Typhi in stool or urine for more than 1 year following acute infection. The gallbladder, particularly in patients with gallstones or structural abnormalities, serves as the primary reservoir for chronic carriage. Chronic carriers are key drivers of ongoing typhoid transmission, as illustrated by the historical case of "Typhoid Mary" (Mary Mallon).

3. Transmission & Epidemiology

Typhoid fever is transmitted exclusively via the fecal-oral route — through the consumption of food or water contaminated by the feces or urine of acutely infected individuals or chronic carriers. There is no animal reservoir.

Global Distribution

Typhoid is endemic in South Asia (India, Pakistan, Bangladesh, Nepal account for the majority of global cases), sub-Saharan Africa, and parts of Southeast Asia. South Asia alone accounts for approximately 70% of the global typhoid burden. The disease is rare in high-income countries with treated water supplies and robust sanitation systems, occurring primarily in travelers returning from endemic regions and in communities with compromised water infrastructure.

Antimicrobial Resistance

The emergence of multidrug-resistant (MDR) typhoid — resistant to ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole (the traditional first-line drugs) — began in the 1990s. More alarming is the XDR typhoid strain (H58 clade 4.3.1) that emerged in Pakistan in 2016, additionally resistant to fluoroquinolones and third-generation cephalosporins, leaving azithromycin and carbapenems as the only reliable oral and parenteral options, respectively. XDR typhoid has since spread to multiple countries.

4. Symptoms by Phase

The clinical course of typhoid fever classically progresses through stepwise weekly phases, though this pattern is not always distinct in practice:

Week 1 — Prodrome and Rising Fever

Gradual onset of fever that rises in a step-ladder pattern, reaching 39–40°C. Associated symptoms: malaise, headache, anorexia, myalgias, abdominal discomfort, and non-productive cough. Relative bradycardia (pulse slower than expected for the degree of fever, a finding called Faget's sign) is a classic but not universally present feature. Leukopenia is typical, helping distinguish typhoid from bacterial pyogenic infections.

Week 2 — Peak Fever and Abdominal Signs

Sustained plateau fever (39–40°C), increasing toxicity, and abdominal findings: diffuse abdominal tenderness, hepatosplenomegaly in the majority of patients, and constipation (more common than diarrhea in the early stages). Rose spots: faint salmon-colored macular or maculopapular rash appearing on the trunk (abdomen, lower chest) in approximately 30–50% of patients, lasting 2–5 days before fading; difficult to see on darker skin tones. Mental status changes — confusion, delirium, prostration ("typhoid state") — may appear in severe cases.

Week 3 — Complications or Defervescence

The critical period. Without treatment, life-threatening complications can develop: intestinal hemorrhage from necrosis of Peyer's patches, intestinal perforation (most feared complication), hepatitis, myocarditis, or neurologic involvement. With adequate antibiotic treatment, fever begins to defervescence around days 5–7 and the patient improves over 1–2 weeks. Relapses occur in 5–10% of patients 2–3 weeks after clinical recovery.

5. Diagnosis

Diagnosis requires clinical suspicion based on fever in a returning traveler or resident of an endemic area, combined with laboratory confirmation.

Blood Culture (Gold Standard)

Blood culture is the most reliable diagnostic test, with sensitivity of 80–90% in the first week of illness (before antibiotics). Sensitivity decreases substantially after antibiotic administration. Multiple blood culture sets (3 sets at 12-hour intervals) increase diagnostic yield. Culture requires 2–5 days for growth of S. Typhi.

Bone Marrow Culture

Bone marrow aspirate culture is the most sensitive test for typhoid fever (sensitivity ~90%) even after several days of antibiotic treatment. It is invasive but valuable when blood cultures are negative and typhoid is strongly suspected.

Widal Test

The Widal agglutination test detects antibodies against O and H antigens of S. Typhi. Widely used in resource-limited settings due to low cost, but has poor specificity (false positives in prior vaccination, other Salmonella infections, and endemic populations with high background serology), variable sensitivity, and requires paired samples for reliable interpretation. Not recommended as the sole diagnostic test in guideline-adherent practice.

Typhoid Rapid Diagnostic Tests (RDTs)

Typhoid IgM lateral flow assays (e.g., Test-It Typhoid, Typhidot) detect anti-S. Typhi IgM antibodies. Sensitivity varies widely (50–80%) by study and population; they perform better in the second week of illness. The TUBEX test (anti-O9 antibody) has slightly better performance. RDTs are useful in endemic low-resource settings but should not replace blood culture when feasible.

PCR

Quantitative PCR for S. Typhi DNA in blood can detect low levels of bacteremia and may identify cases earlier than culture; high sensitivity and specificity, but not yet standardized or widely available.

6. Treatment

Antibiotic Selection Based on Susceptibility

Treatment must be guided by local resistance patterns. Given the spread of XDR typhoid from South Asia, empiric therapy should account for likely origin:

Fluoroquinolone-susceptible typhoid: Ciprofloxacin 500 mg PO twice daily × 5–7 days, or ofloxacin 400 mg PO twice daily × 5 days — highly effective (cure rates >95%); avoid if from South Asia/Pakistan where fluoroquinolone resistance is common.
Fluoroquinolone-resistant (non-XDR) typhoid: Azithromycin 1 g PO on day 1, then 500 mg daily × 6 days (for uncomplicated typhoid); ceftriaxone 2–4 g IV daily × 10–14 days for severe disease.
XDR typhoid (Pakistan-origin, resistant to fluoroquinolones + cephalosporins): Azithromycin 20 mg/kg/day PO (max 1 g) × 7 days for uncomplicated disease. Meropenem 1 g IV every 8 hours for severe or complicated XDR typhoid.
Pediatric dosing: Azithromycin 20 mg/kg/day and ceftriaxone 75 mg/kg/day are preferred in children; fluoroquinolones are generally avoided in children under 18 due to theoretical joint toxicity, though used when benefits outweigh risks.
Dexamethasone (3 mg/kg loading dose, then 1 mg/kg every 6 hours for 48 hours) is recommended for patients with severe typhoid complicated by delirium, obtundation, stupor, coma, or shock — reduces mortality in severe disease.

Chronic Carriage Treatment

Fluoroquinolones for 28 days (ciprofloxacin 750 mg PO twice daily) achieve microbiologic cure in approximately 80% of carriers without structural biliary disease. Cholecystectomy combined with antibiotic therapy is required for carriers with gallstones or other biliary pathology unresponsive to antibiotics.

7. Home & Supportive Care

Patients with uncomplicated typhoid who are able to take oral antibiotics and fluids can often be managed at home with close follow-up:

Hydration: Typhoid causes significant insensible fluid losses through fever; ensure 2.5–3 liters of fluid intake daily. ORS is useful if diarrhea is present.
Fever management: Paracetamol every 6 hours — avoid NSAIDs, which can increase gastrointestinal bleeding risk in a disease that can affect Peyer's patches.
Diet: Soft, easily digestible foods — congee, boiled rice, bananas, cooked vegetables. Avoid high-fiber foods, raw vegetables, and spicy foods during acute illness; high residue can worsen bowel wall stress where ulceration may be occurring.
Activity restriction: Complete bed rest is recommended during the febrile phase; physical exertion can theoretically increase risk of intestinal perforation.
Strict hygiene: Hand washing after toilet use is critical to prevent transmission to household contacts. Food preparation should be delegated to an uninfected person until the patient is culture-negative.
Warning signs requiring hospital assessment: Severe abdominal pain (especially with rebound tenderness — may indicate perforation), signs of bleeding (rectal blood or melaena), altered consciousness, respiratory distress, or failure to improve after 5 days of antibiotics.

8. Complications

Intestinal perforation: Occurs in 1–3% of untreated cases (more common in children and adolescents) from necrosis and ulceration of Peyer's patches in the terminal ileum. Presents as sudden worsening of abdominal pain, rigidity, and peritoneal signs. Requires emergency laparotomy with primary repair or segmental resection; mortality even with surgery is 10–30%.
Intestinal hemorrhage: Significant GI bleeding from ulcerated Peyer's patches in approximately 1–3%; managed with transfusion and hemostasis; may require surgery.
Hepatitis: Transaminase elevation in up to 50% of cases; rarely progresses to hepatic failure.
Myocarditis and pericarditis: Occur in approximately 1–5%; may manifest as arrhythmia, conduction defects, or heart failure.
Neuropsychiatric typhoid: Encephalopathy, meningism, delirium, and psychosis in severe disease; cranial nerve palsies, cerebellar ataxia, and Guillain-Barré syndrome are rare.
Relapse: Occurs in 5–10% of treated patients, typically 2–3 weeks after defervescence. Relapses are usually milder than the primary episode; treat with antibiotics based on sensitivities.
Hemophagocytic lymphohistiocytosis (HLH): Rare but life-threatening complication of typhoid fever, presenting as unremitting fever, cytopenia, and hyperferritinemia.

9. Prevention & Vaccines

Sanitation and Water Safety

The most effective long-term prevention is safe water, sanitation, and hygiene (WASH): chlorinated water supplies, sewage treatment, food safety, and hand hygiene education. These interventions have eliminated endemic typhoid from high-income countries.

Travel Precautions

Travelers to endemic regions should follow strict food and water precautions: drink only bottled or boiled water, eat only thoroughly cooked food and pasteurized dairy, avoid raw fruits and vegetables that cannot be peeled, and avoid street food. These measures substantially reduce (but do not eliminate) risk.

Typhoid Conjugate Vaccine (TCV) — Preferred

Typhoid conjugate vaccines (Typbar-TCV, PedaTyph, Typhi-TEV) couple the Vi polysaccharide antigen to a carrier protein (tetanus toxoid), producing T-cell-dependent immunity, longer-lasting protection, and immunogenicity in children under 2 years. WHO prequalified Typbar-TCV (Bharat Biotech) has demonstrated 81.6% efficacy in a phase 3 trial in Nepal and 82–87% efficacy in Malawi. Recommended from 6 months of age, with a single dose; boostability established. WHO recommends TCV as the preferred typhoid vaccine for programmatic use.

Vi Polysaccharide Vaccine (Typhim Vi, Typherix)

Single IM dose; efficacy approximately 60–70%, duration of protection 3 years. Not immunogenic in children under 2 years due to T-cell independence. Used in travelers from age 2 years; requires repeat dosing every 3 years if ongoing exposure.

Oral Ty21a Vaccine (Vivotif)

Live attenuated oral vaccine; 4 capsules taken on alternate days. Efficacy approximately 50–67% in endemic populations; 3–7 years protection. Must be refrigerated; contraindicated in immunocompromised individuals and during antibiotic use. Used in travelers from age 6 years.

10. Key Research Papers

Crump JA, Luby SP, Mintz ED. The global burden of typhoid fever. Bull World Health Organ. 2004;82:346–353. PMID: 15298225.
Parry CM, Hien TT, Dougan G, et al. Typhoid fever. N Engl J Med. 2002;347:1770–1782. PMID: 12456854.
Pitzer VE, Bowles CC, Baker S, et al. Predicting the impact of vaccination on the transmission dynamics of typhoid in South Asia. PLOS Negl Trop Dis. 2014;8:e1521. PMID: 24516683.
Shakya M, Colin-Jones R, Theiss-Nyland K, et al. Phase 3 Efficacy Analysis of a Typhoid Conjugate Vaccine Trial in Nepal. N Engl J Med. 2019;381:2209–2218. PMID: 31774954.
Klemm EJ, Shakoor S, Page AJ, et al. Emergence of an extensively drug-resistant Salmonella enterica serovar Typhi clone harboring a promiscuous plasmid encoding resistance to fluoroquinolones and third-generation cephalosporins. mBio. 2018;9:e00105-18. PMID: 29463654.
Britto C, Pollard AJ, Voysey M, Blohmke CJ. An appraisal of the clinical features of pediatric enteric fever: systematic review and meta-analysis of the age-stratified disease occurrence. Clin Infect Dis. 2017;64:1604–1611. PMID: 28475731.
Darton TC, Blohmke CJ, Moorthy VS, et al. Design, recruitment, and microbiological considerations in human challenge studies. Lancet Infect Dis. 2015;15:840–851. PMID: 26026083.
Thaver D, Zaidi AK. Burden of neonatal infections in developing countries: a review of evidence from community-based studies. Pediatr Infect Dis J. 2009;28:S3–S9. PMID: 19106768.
Andrews JR, Ryan ET. Diagnostics for invasive Salmonella infections: current challenges and future directions. Vaccine. 2015;33:C8–C15. PMID: 26116628.
Wain J, Hendriksen RS, Mikoleit ML, et al. Typhoid fever. Lancet. 2015;385:1136–1145. PMID: 25458731.
Srikantiah P, Medalla F, Whichard JM, et al. Emergence of fluoroquinolone-resistant Salmonella Typhi. Emerg Infect Dis. 2006;12:1175–1177. PMID: 16836838.
Milligan R, Paul M, Richardson M, Neuberger A. Vaccines for preventing typhoid fever. Cochrane Database Syst Rev. 2018;5:CD001261. PMID: 29851031.

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