Typhoid fever is a severe infection caused by a bacterium, Salmonella typhi. S. typhi is in the same family of bacteria as the type spread by chicken and eggs, commonly known as "salmonella poisoning," or food poisoning. S. typhi bacteria do not have vomiting and diarrhea as the most prominent symptoms of their presence in humans. Instead, persistently high fever is the hallmark of S. typhi infection.
Description
S. typhi bacteria are passed into the stool and urine of infected patients. They may continue to be present in the stool of asymptomatic carriers, who are persons who have recovered from the symptoms of the disease but continue to carry the bacteria. This carrier state occurs in about 3% of all individuals recovered from typhoid fever.
Typhoid fever is passed from person to person through poor hygiene, such as incomplete or no hand washing after using the toilet. Persons who are carriers of the disease and who handle food can be the source of epidemic spread of typhoid. One such individual gave her name to the expression "Typhoid Mary," a name given to someone whom others avoid.
Typhoid fever is a particularly difficult problem in parts of the world with poor sanitation practices. In the United States, most patients who contract typhoid fever have recently returned from travel to another country where typhoid is much more common, including Mexico, Peru, Chile, India, and Pakistan.
Causes and symptoms
S. typhi must be ingested to cause disease. Transmission often occurs when a person in the carrier state does not wash hands thoroughly (or not at all) after defecation and serves food to others. This pathway is sometimes called the fecal-oral route of disease transmission. In countries where open sewage is accessible to flies, the insects land on the sewage, pick up the bacteria, and then contaminate food to be eaten by humans.
After being swallowed, the S. typhi bacteria head down the digestive tract, where they are taken in by cells called mononuclear phagocytes. These phagocytes are cells of the immune system, whose job it is to engulf and kill invading bacteria and viruses. In the case of S. typhi, however, the bacteria are able to survive ingestion by the phagocytes, and multiply within these cells. This period of time, during which the bacteria are multiplying within
the phagocytes, is the 10- to 14-day incubation period of typhoid fever. When huge numbers of bacteria fill an individual phagocyte, they spill out of the cell and into the bloodstream, where their presence begins to cause symptoms.
The presence of increasingly large numbers of bacteria in the bloodstream (bacteremia) is responsible for an increasingly high fever, which lasts throughout the four to eight weeks of the disease in untreated individuals. Other symptoms of typhoid fever include constipation (at first), extreme fatigue, headache, joint pain, and a rash across the abdomen known as rose spots.
The bacteria move from the bloodstream into certain tissues of the body, including the gallbladder and lymph tissue of the intestine (called Peyer's patches). The tissue's response to this invasion causes symptoms ranging from inflammation of the gallbladder (cholecystitis) to intestinal bleeding to actual perforation of the intestine. Perforation of the intestine refers to an actual hole occurring in the wall of the intestine, with leakage of intestinal contents into the abdominal cavity. This leakage causes severe irritation and inflammation of the lining of the abdominal cavity, which is called peritonitis. Peritonitis is a frequent cause of death from typhoid fever.
Other complications of typhoid fever include liver and spleen enlargement, sometimes so great that the spleen ruptures or bursts; anemia, or low red blood cell count due to blood loss from the intestinal bleeding; joint infections, which are especially common in patients with sickle cell anemia and immune system disorders; pneumonia caused by a bacterial infection—usually Streptococcus pneumoniae—which is able to take hold due to the patient's weakened state; heart infections; and meningitis and infections of the brain, which cause mental confusion and even coma. It may take a patient several months to recover fully from untreated typhoid fever.
Diagnosis
In some cases, the doctor may suspect the diagnosis if the patient has already developed the characteristic rose spots, or if he or she has a history of recent travel in areas with poor sanitation. The diagnosis, however, is confirmed by a blood culture. Samples of a patient's stool, urine, and bone marrow can also be used to grow S. typhi in a laboratory for identification under a microscope. Cultures are the most accurate method of diagnosis. Blood cultures usually become positive in the first week of illness in 80% of patients who have not taken antibiotics.
Treatment
Antibiotics are the treatment of choice for typhoid fever. Chloramphenicol (Chloromycetin) is the most effective medication for S. typhi. The patient's symptoms begin to improve slightly after only 24-48 hours of receiving the medication. Another drug, ceftriaxone (Rocephin), has been used as well, and is also extremely effective. It lowers fever fairly quickly.
Carriers of S. typhi must be treated even when they do not show any symptoms of the infection, because carriers are responsible for the majority of new cases of typhoid fever. Eliminating the carrier state is actually a fairly difficult task. It requires treatment with one or even two different medications over a period of four to six weeks. In the case of a carrier with gallstones, surgery may need to be performed to remove the gallbladder. This measure is necessary because typhoid bacteria are often housed in the gallbladder, where they may survive in spite of antibiotic treatment.
Prognosis
The prognosis for recovery is good for most patients. In the era before effective antibiotics were discovered, about 12% of all typhoid fever patients died of the infection. Now, however, fewer than 1% of patients who receive prompt antibiotic treatment will die. The mortality rate is highest in the very young and very old, and in patients suffering from malnutrition. The most ominous signs are changes in a patient's state of consciousness, including stupor or coma.
Prevention
Hygienic sewage disposal systems in a community as well as proper personal hygiene are the most important factors in preventing typhoid fever. Immunizations are available for travelers who expect to visit countries where S. typhi is a known public health problem. Some of these immunizations provide only short-term protection (for a few months), while others may be effective for several years. Efforts are being made to develop immunizations that provide a longer period of protection with fewer side effects from the vaccine itself.
BOOKS
"Salmonellosis." In Sherris Medical Microbiology: An Introduction to Infectious Diseases. 3rd ed. Ed. Kenneth J. Ryan. Norwalk, CT: Appleton & Lange, 1994.
Stoffman, Phyllis. The Family Guide to Preventing and Treating 100 Infectious Diseases. New York: John Wiley & Sons, 1995.
PERIODICALS
Zenilman, J. M. "Typhoid Fever." Journal of the American Medical Association (10 Sept. 1997): 847+.
ORGANIZATIONS
Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311. <http://www.cdc.gov>.
Rosalyn Carson-DeWitt, MD
KEY TERMS
Asymptomatic—A state in which a person experiences no symptoms of a disease.
Bacteremia—Bacteria in the blood.
Carrier—A person who has a particular disease agent present within his/her body, and can pass this agent on to others, but who displays no symptoms of infection.
Epidemic—A large number of cases of the same disease or infection all occurring within a short time period in a specific location.
Mononuclear phagocyte—A type of cell of the human immune system that ingests bacteria, viruses, and other foreign matter, thus removing potentially harmful substances from the bloodstream. These substances are usually then digested within the phagocyte.
Rose spots—A pinkish rash across the trunk or abdomen that is a classic sign of typhoid fever.
