Typhoid fever, also known as enteric fever, is a serious, life-threatening infection caused by the bacterium Salmonella enterica serovar Typhi (often simply called Salmonella Typhi). It is a systemic disease, meaning it affects the entire body, and is particularly prevalent in areas with poor sanitation and a lack of safe drinking water.
Cause and Transmission
Typhoid fever is solely a human-borne disease; the bacterium Salmonella Typhi lives only in humans, and no animal reservoir exists.
Causative Agent
The infection is caused by the Gram-negative bacterium Salmonella enterica serovar Typhi.
Mode of Transmission
Typhoid fever is transmitted through the fecal-oral route. This occurs when a person ingests food or water contaminated with the feces of an infected person.
- Contaminated Water and Food: The most common sources are water, ice, or foods (especially raw fruits, vegetables, and shellfish) that have been contaminated by sewage or handled by an infected person.
- Chronic Carriers: Some individuals, known as chronic carriers (like the historical "Typhoid Mary"), continue to harbor the bacteria, usually in their gallbladder, and shed them in their feces for months or even years after recovering from the acute illness, potentially spreading the disease to others.
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Symptoms and Course of Infection
The incubation period for typhoid fever typically ranges from 6 to 30 days after exposure.
Early Symptoms (Week 1)
- Prolonged, Stepwise Fever: The hallmark symptom is a fever that increases gradually over several days, often reaching as high as 104∘F(40∘ C).
- Headache
- Malaise (general feeling of discomfort or illness)
- Fatigue
- Cough
- Abdominal pain
Peak Illness (Weeks 2-3)
If untreated, the fever remains high, and more severe symptoms appear:
- Prostration (extreme weakness)
- Rose Spots: A characteristic rash of small, faint, rose-colored spots may appear on the lower chest and abdomen in about a third of patients.
- Gastrointestinal Issues: Constipation is often more common than diarrhea in adults, while diarrhea is more typical in children.
- Abdominal Distension
- Hepatosplenomegaly: Enlargement of the liver and spleen.
- "Nervous Fever": Confusion, delirium, or a state of being too tired to get up (sometimes called "coma vigil" in severe cases) may occur.
Complications
Without prompt treatment, typhoid fever can lead to severe and life-threatening complications, usually during the third week of illness:
- Intestinal Hemorrhage: Severe gastrointestinal bleeding.
- Intestinal Perforation: A critical complication where a hole develops in the wall of the small intestine (usually the distal ileum), leading to peritonitis and sepsis, which is often fatal.
- Encephalitis (brain inflammation)
- Pneumonia
- Myocarditis (heart muscle inflammation)
Diagnosis and Treatment
Diagnosis
Diagnosis is typically confirmed by identifying S. Typhi in clinical samples:
- Blood Culture: Most reliable during the first week of fever.
- Bone Marrow Culture: Considered the most sensitive test, as the bacteria are often present even after antibiotic treatment has started.
- Stool or Urine Culture: Used for later diagnosis and for identifying chronic carriers.
- Serological Tests (e.g., Widal test): Used to look for antibodies against the bacteria, but their reliability is limited due to potential cross-reactions and delays in antibody production.
Treatment
Antibiotics are the only effective treatment for typhoid fever.
- First-line treatment depends on the local patterns of antibiotic resistance. Commonly used drugs include fluoroquinolones (like ciprofloxacin, though resistance is increasing), azithromycin, and ceftriaxone.
- Supportive Care includes fluid and electrolyte replacement to prevent dehydration, and adequate rest.
- Drug Resistance: The rise of multi-drug resistant (MDR) and extensively drug-resistant (XDR) strains of S. Typhi is a major public health concern, making treatment more complicated and expensive.
Prevention
Prevention strategies combine public health interventions and individual protective measures.
Public Health Measures
- Safe Water and Sanitation (WASH): Providing access to clean drinking water and adequate sanitation (sewage disposal) is the cornerstone of long-term typhoid prevention.
- Food Safety: Ensuring proper hygiene among food handlers and regulating food preparation, especially street food, is crucial.
Vaccination
Vaccination is an important tool, particularly for travelers to endemic regions and for people living in high-risk areas. Two main types of vaccines are available:
- Injectable Vi Polysaccharide Vaccine (ViCPS): An inactivated vaccine, generally recommended for people 2 years of age and older.
40 Requires a booster dose every 2-3 years. - Oral Live Attenuated Vaccine (Ty21a): A live vaccine given in multiple doses (typically 4 capsules on alternating days), generally recommended for people 6 years of age and older. Requires a booster dose every 5 years.
- Typhoid Conjugate Vaccines (TCV): The World Health Organization (WHO) preferentially recommends TCVs because they offer longer protection, require only a single dose, and are safe and effective for children as young as 6 months of age, making them suitable for routine childhood immunization programs in endemic countries.
Traveler's Precautions
Travelers to areas where typhoid fever is common should follow strict food and water precautions:
- Boil it, cook it, peel it, or forget it!
- Drink only bottled or boiled water. Avoid ice unless you know it's made from safe water.
- Eat food that is properly cooked and served hot.
- Avoid raw fruits and vegetables that you cannot peel yourself.
- Wash hands frequently with soap and water, especially before eating and after using the toilet.
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