Typhoid is a serious bacterial infection caused by Salmonella Typhi, a pathogen that spreads through contaminated water and food. It affects roughly 9 million people worldwide each year and kills about 110,000, with most cases concentrated in parts of South Asia, sub-Saharan Africa, and Southeast Asia. Unlike the common food poisoning caused by other Salmonella species, typhoid enters the bloodstream and can affect multiple organs, making it far more dangerous if left untreated.
How Typhoid Spreads
Typhoid is a fecal-oral infection. The bacteria leave the body in the stool of an infected person, and new infections happen when those bacteria find their way into someone else’s mouth, almost always through contaminated drinking water or food. This is why typhoid thrives in places with poor sanitation, unreliable water treatment, or overcrowded living conditions. Even a relatively small number of bacteria, as few as a thousand organisms, can be enough to cause infection.
One of the trickiest aspects of typhoid is the carrier state. Between 3% and 5% of people who recover from the infection become chronic carriers, meaning they continue shedding bacteria in their stool for months or years without feeling sick themselves. The bacteria survive by attaching to gallstones and forming a protective coating called a biofilm, which shields them from both the immune system and antibiotics. These carriers can unknowingly contaminate food or water and spark new outbreaks. The most famous example in history, “Typhoid Mary,” was a chronic carrier who worked as a cook in early 1900s New York.
What the Bacteria Do Inside Your Body
After you swallow contaminated food or water, the bacteria must first survive your stomach acid, which acts as a natural barrier. Those that make it through reach the small intestine, where they actively invade the cells lining the gut wall. Salmonella Typhi carries a molecular needle-like structure that injects proteins into intestinal cells, forcing them to rearrange their internal scaffolding and essentially pull the bacteria inside.
What makes Salmonella Typhi different from the Salmonella strains that cause ordinary food poisoning is a protective capsule called the Vi antigen. This capsule acts like a cloak, hiding the bacteria from immune cells and preventing them from being destroyed in the bloodstream. The bacteria also produce a unique toxin that enters host cells and damages their DNA, triggering cell death. This toxin is found only in typhoid-causing strains and is responsible for many of the disease’s characteristic symptoms.
Symptoms and How They Progress
Typhoid doesn’t hit all at once. After an incubation period of 6 to 30 days (typically 10 to 14), the illness begins gradually. The first sign is usually a slowly climbing fever that increases in a stepladder pattern, reaching 38 to 40°C (100.4 to 104°F) by the third or fourth day. Alongside the fever, you’ll typically notice fatigue, headache, loss of appetite, and a general sense of feeling unwell. Abdominal discomfort is common early on, and some people develop a slower-than-expected heart rate relative to their fever during the first week.
Without treatment, the disease intensifies over the following weeks. The fever stays persistently high, abdominal symptoms worsen, and complications become more likely. The most dangerous complication is intestinal perforation, where the bacteria erode through the wall of the intestine. This occurs in a wide range of untreated cases, and when it happens in resource-limited settings, the mortality rate typically falls between 11% and 30%.
How Typhoid Is Diagnosed
Diagnosing typhoid can be surprisingly difficult because its early symptoms overlap with many other infections. The gold standard is a blood culture, where a sample of your blood is tested for the presence of Salmonella Typhi. When it detects the bacteria, a blood culture is 100% specific, meaning it never produces a false positive. The catch is that it only picks up about 15% of actual cases, so a negative result doesn’t rule typhoid out. Blood cultures are most useful during the first week of illness.
Doctors also use a blood test called the Widal test, which looks for antibodies your immune system produces in response to the infection rather than the bacteria themselves. The Widal test catches about 65% of cases but occasionally gives false positives, with a specificity around 90%. It works best during the second week of illness, after your body has had time to mount an immune response. In practice, doctors often combine multiple test results with clinical judgment, especially in areas where typhoid is common.
Treatment and Drug Resistance
Antibiotics are recommended for all patients with typhoid fever, and when the bacteria are susceptible to standard drugs, treatment is straightforward and highly effective. The challenge is that Salmonella Typhi has been steadily developing resistance to the antibiotics that once worked reliably against it.
The most alarming development is the emergence of extensively drug-resistant (XDR) strains. First identified in Pakistan in 2016, these strains resist nearly all commonly used antibiotics, including one called ceftriaxone that had been a go-to treatment. XDR typhoid has since spread to travelers visiting Pakistan and neighboring countries, and cases have appeared in the United States in people who never left the country. Because of this resistance, the CDC now recommends that doctors use lab testing to determine exactly which antibiotics will work before choosing a treatment, rather than relying on standard first-line options.
Vaccination
Two types of typhoid vaccines are available, but the newer typhoid conjugate vaccine (TCV) has become the preferred option, especially for children. In a large clinical trial in Malawi, a single dose of TCV provided 78% protection against typhoid fever, with that protection holding steady over a median follow-up of more than four years. The vaccine worked across all age groups tested, including children as young as 9 months, with efficacy ranging from about 71% in the youngest children to nearly 80% in those aged 2 to 12.
The World Health Organization now recommends TCV for mass vaccination campaigns targeting children 9 months to 15 years old in typhoid-endemic areas, followed by routine vaccination in the first two years of life. For travelers heading to high-risk regions, vaccination is a practical layer of protection, though it’s not a substitute for careful food and water hygiene. Avoiding untreated tap water, raw foods washed in local water, and street food from vendors with questionable sanitation practices remains the most reliable way to reduce your risk.