Meaning
Salmonella Typhi (S. Typhi) is a bacterium that causes typhoid fever, a systemic infection transmitted mainly through contaminated food and water.
Unlike many other Salmonella species that infect both animals and humans, S. Typhi is primarily human-restricted.
Transmission
Typhoid spreads through the faeco-oral route.
Common pathways include:
- contaminated drinking water;
- food handled by an infected person;
- poor sanitation and sewage disposal;
- inadequate hand hygiene.
The chain is broadly:
Infected person → Faecal contamination → Food/Water → New infection
What Happens in the Body?
After ingestion, S. Typhi:
- crosses the intestinal lining;
- survives inside immune cells;
- spreads through the bloodstream;
- can reach organs such as the liver, spleen and bone marrow.
This ability to spread beyond the intestine makes typhoid a systemic disease, unlike ordinary food poisoning.
Major Symptoms
Common features include:
- prolonged fever;
- headache;
- weakness;
- abdominal discomfort;
- loss of appetite;
- constipation or diarrhoea.
Severe untreated disease may cause:
- intestinal bleeding;
- intestinal perforation;
- sepsis;
- neurological complications.
Diagnosis
Diagnosis may involve:
- blood culture, especially early in illness;
- bone-marrow culture in difficult cases;
- other microbiological tests.
The traditional Widal test has important limitations and should not be relied upon alone for definitive diagnosis.
Treatment
Typhoid is treated with appropriate antibiotics, but treatment has become more difficult because of antimicrobial resistance (AMR).
Drug-resistant and extensively drug-resistant strains of S. Typhi have emerged in several regions, making laboratory-guided treatment increasingly important.
Carrier State
Some individuals continue to carry S. Typhi after recovering and may shed the bacteria without symptoms.
The gallbladder can act as an important reservoir in chronic carriers.
Such carriers can contribute to continued community transmission.
Prevention
Key measures include:
- safe drinking water;
- sanitation and sewage treatment;
- hand hygiene;
- food safety;
- identification and treatment of carriers;
- typhoid vaccination.
Typhoid Conjugate Vaccine
Typhoid Conjugate Vaccines (TCVs) provide longer-lasting protection and can be used in younger children compared with older typhoid vaccines.
They are especially important in areas with:
- high disease burden;
- poor sanitation;
- increasing antimicrobial resistance.
S. Typhi vs Non-Typhoidal Salmonella
S. Typhi: primarily causes systemic typhoid fever and is human-restricted.
Non-typhoidal Salmonella: more commonly causes gastroenteritis and often has animal reservoirs.
Why It Matters for India
Typhoid remains important because of:
- dense populations;
- uneven sanitation;
- contaminated water risks;
- antimicrobial resistance;
- need for stronger vaccination and surveillance.
Key Takeaway
Salmonella Typhi → Human-restricted bacterium → Faeco-oral transmission → Typhoid fever → Increasing AMR challenge
