How is infection with Salmonella typhi acquired?

How Typhoid Fever is Acquired

Typhoid fever is acquired through the fecal-oral route by ingesting food or water contaminated with Salmonella Typhi from infected individuals or chronic carriers. 1

Primary Transmission Routes

Contaminated Food and Water

• The most common mode of transmission is consumption of food or water contaminated with S. Typhi from fecal matter of infected persons or chronic carriers. 2, 3
• Transmission is facilitated by poor sanitation and inadequate hygiene practices in endemic areas. 3
• In the United States, typhoid outbreaks are uncommon but typically associated with foodborne transmission from asymptomatic carriers. 1

Geographic Risk Factors

• Typhoid fever incidence is highest in South and Southeast Asia, with moderate risk in Central and South America, Africa, Central and East Asia, and Oceania. 1
• Among U.S. cases from 2004-2009,68% of S. Typhi infections and 50% of S. Paratyphi infections were travel-related. 1
• Risk is greatest for travelers to developing countries who have prolonged exposure to potentially contaminated food and drink. 1

Less Common Transmission Routes

Household and Close Contact

• Intimate exposure to a documented typhoid carrier (such as household contact) represents a significant transmission risk. 1
• Person-to-person transmission can occur through direct contact when proper hand hygiene is not followed. 1

Laboratory Exposure

• Microbiologists and laboratory personnel working with S. Typhi cultures are at risk for laboratory-acquired infection. 1
• During 1985-1994, seven cases of laboratory-acquired typhoid were reported among microbiology workers in the U.S. 1
• Laboratory-acquired cases represented 11.2% of sporadic typhoid cases in one study, with 21 of 24 cases occurring during educational or proficiency testing. 4
• Recent cases have occurred despite working in biosafety cabinets, emphasizing ongoing risk. 5

Sexual Transmission

• Sexually acquired S. Typhi urinary tract infections have been documented, particularly in men who have sex with men. 6

Critical Prevention Points

Hand Hygiene

• Hand hygiene must be performed after using the toilet, changing diapers, before and after preparing food, before eating, and after handling garbage or soiled laundry. 1
• Hand hygiene with soap and water or alcohol-based sanitizers should be used in care of people with diarrhea. 1

Food Safety

• Appropriate food safety practices are essential, including avoiding cross-contamination and ensuring meats and eggs are cooked and maintained at proper temperatures. 1
• Travelers should avoid unpasteurized dairy products and undercooked meat. 1

Vaccination for High-Risk Groups

• Typhoid vaccination is recommended for travelers to endemic areas, household contacts of chronic carriers, and laboratory personnel routinely exposed to S. Typhi cultures. 1
• Two vaccines are available: oral live-attenuated Ty21a (4-dose series) and injectable Vi polysaccharide vaccine (single dose). 1
• Both vaccines provide 50-80% protection and require boosters every 5 years (oral) or 2 years (injectable). 1

Common Pitfalls

• Typhoid vaccination is not a substitute for careful food and water selection, as vaccines are not 100% effective and protection can be overwhelmed by large inocula. 1
• Asymptomatic chronic carriers can shed S. Typhi for over a year after acute infection, particularly if they have gallbladder pathology or urinary tract abnormalities. 1, 7
• The portal of entry is the gastrointestinal tract, though diarrhea is actually an uncommon feature of typhoid fever itself. 1