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In the year 1906, 3,000 New York state residents contracted typhoid fever, a contagious and life-threatening bacterial illness. A feisty Irish cook named Mary Mallon seems to have infected only a small percentage of these people, yet she became so identified in the public mind with the epidemic that she was dubbed Typhoid Mary and was quarantined for life on an island in the Hudson River.

Today, typhoid fever is rare in industrialized countries, although it remains a serious health threat in the developing world.

Typhoid fever spreads through contaminated food and water or through close contact with someone who's infected. Signs and symptoms usually include high fever, headache, abdominal pain and either constipation or diarrhea. A related condition, paratyphoid fever, causes similar problems, but in a milder form.

When treated with antibiotics, most people feel better within a few days, although a small percentage — especially older adults and those with chronic diseases — may die of complications. And a few people, like Mary Mallon, continue to carry the bacteria in their bodies and to infect others, even though they appear healthy.

Vaccines against typhoid fever are available, but they're only partially effective and are usually reserved for people who may be exposed to the disease or are traveling to areas where typhoid fever is endemic.

Although children with typhoid fever sometimes become sick suddenly, signs and symptoms are more likely to develop gradually — often appearing one to three weeks after exposure to the disease. In some cases you may not become sick for as long as two months after exposure. The incubation period for paratyphoid fever is shorter — usually one to 10 days.

Once signs and symptoms do appear, you're likely to experience:

• Fever, often as high as 103 or 104 F (39 or 40 C).
• Headache.
• Weakness and fatigue.
• A sore throat.
• Abdominal pain.
• Diarrhea or constipation. Children are more likely to have diarrhea whereas adults may become severely constipated.

During the second week, you may develop a rash of small, flat, rose-colored spots on your lower chest or upper abdomen. The rash is temporary, usually disappearing in three or four days.

Second stage
If you don't receive treatment for typhoid fever, you may enter a second stage during which you become very ill. Your fever will remain high, and you may develop either diarrhea that has the color and consistency of pea soup or severe constipation. You may lose considerable weight during this phase, and your abdomen may become extremely distended.

The typhoid state
By the third week, you may become delirious, lying motionless and exhausted with your eyes half-closed in what's known as the typhoid state. Life-threatening complications often develop at this time.

Improvement
Improvement may come slowly during the fourth week. Your fever is likely to decrease gradually until your temperature returns to normal in another week to 10 days. But signs and symptoms can return up to two weeks after your fever has subsided.

Paratyphoid fever causes signs and symptoms similar to those of typhoid fever, but in a milder form. Complications aren't as severe, and you generally recover more quickly.

Typhoid fever appears to have afflicted human beings for millennia, but the cause of the illness — a virulent and invasive bacterium called Salmonella typhi — wasn't discovered until the late 19th century. A different pathogen, Salmonella paratyphi, causes paratyphoid fever. Although they're related, these aren't the same as the bacteria responsible for salmonellosis, another serious intestinal infection.

Fecal-oral route
The bacteria that cause typhoid and paratyphoid fever both spread through contaminated food or water and occasionally through direct contact with someone who is already infected. In developing nations, where typhoid and paratyphoid are endemic, most cases result from contaminated drinking water and poor sanitation. The majority of people in industrialized countries pick up the typhoid bacteria while traveling and spread it to others through the fecal-oral route.

This means that S. typhi and S. paratyphi are passed in the feces and sometimes in the urine of infected people. You can contract the infection if you eat food handled by someone with typhoid fever who hasn't washed carefully after using the bathroom. You can also become infected by drinking water contaminated with the bacteria.

Typhoid carriers
Even after treatment with antibiotics, a small number of people who recover from typhoid fever continue to harbor the bacteria in their intestinal tract or gallbladder, often for years. These people, called chronic carriers, shed the bacteria in their feces and are capable of infecting others, although they no longer have signs or symptoms of the disease themselves.

Typhoid fever remains a serious threat in the developing world, where it affects more than 12 million people annually. The disease is endemic in India, Southeast Asia, Africa, South America and in certain regions of the former Soviet Union, especially Tajikistan and Uzbekistan.

Worldwide, children are at greatest risk of contracting the disease, although they generally have milder symptoms and fewer complications than adults do.

If you live in a country where typhoid and paratyphoid fevers are rare, you're at increased risk if you:

• Work in or travel to areas where typhoid fever is endemic
• Have close contact with someone who is infected or has recently been infected with typhoid fever
• Have an immune system weakened by medications such as corticosteroids or diseases such as HIV/AIDS
• Drink water contaminated by sewage that contains S. typhi

See a doctor immediately if you suspect you have typhoid fever. If you become ill while traveling in a foreign country, call the U.S. Consulate for a list of doctors. Better yet, find out in advance about medical care in the areas you'll visit, and carry a list of the names, addresses and phone numbers of recommended English-speaking doctors. Your doctor, local or state medical society, the International Association for Medical Assistance to Travellers or the Department of State's Office of Overseas Citizens Services can help provide the information you need.

If you develop signs and symptoms once you return home, consider consulting a doctor who focuses on international travel medicine or infectious diseases. A specialist may be able to recognize and treat your illness more quickly than a doctor who isn't trained in these areas can.

Your doctor is likely to suspect typhoid or paratyphoid fever based on your symptoms and your medical and travel history. But the diagnosis is usually confirmed by identifying S. typhi or S. paratyphi in a culture of your blood or other body fluid or tissue.

For the culture, a small sample of your blood, stool, urine or bone marrow is placed on a special medium that encourages the growth of bacteria. In 48 to 72 hours, the culture is checked under a microscope for the presence of typhoid bacteria. A bone marrow culture often is the most sensitive test for S. typhi.

Your doctor may recommend other tests to help diagnose typhoid fever, such as:

• Enzyme-linked immunosorbent assay (ELISA). This blood test looks for an antigen that's specific to typhoid bacteria. An antigen is any substance, such as a virus, bacterium, toxin or foreign protein, that triggers an immune system response in your body.
• Fluorescent antibody test. This test checks for antibodies to S. typhi. Antibodies are proteins produced by your immune system in response to harmful substances (antigens). Each antibody is unique and defends your body against a single antigen.

The most serious complication of typhoid fever — intestinal bleeding or perforation — may develop in the third week of illness. About 5 percent of people with typhoid fever experience this complication.

Intestinal bleeding is often marked by a sudden drop in blood pressure and shock, followed by the appearance of blood in your stool.

A perforated intestine occurs when your small intestine or large bowel develops a hole, causing intestinal contents to leak into your abdominal cavity and triggering signs and symptoms such as severe abdominal pain, nausea, vomiting and blood stream infection (sepsis). This life-threatening emergency requires immediate medical care — intestinal perforation causes nearly a quarter of the deaths that occur from typhoid fever.

Other, less common complications of typhoid fever include:

• Inflammation of the heart muscle (myocarditis)
• Pneumonia
• Inflammation of the pancreas (pancreatitis)
• Kidney or bladder infections
• Infections of the spine (osteomyelitis)
• Infection and inflammation of the membranes and fluid surrounding your brain and spinal cord (meningitis)
• Psychiatric problems such as delirium, hallucinations and paranoid psychosis

With prompt treatment, nearly all people in industrialized nations recover from typhoid, but without treatment, some people may not survive complications of the disease.

Antibiotic therapy is the only effective treatment for typhoid and paratyphoid fevers. In the past, the drug of choice was chloramphenicol. Doctors no longer commonly use it, however, because of severe side effects, a high relapse rate and widespread bacterial resistance. In fact, the existence of antibiotic-resistant bacteria is a serious and growing problem in the treatment of typhoid, especially in the developing world.

When bacteria prove resistant to standard antibiotics, illnesses last longer, and the risks of complications and death increase. What's more, failure to treat an infection properly leads to longer periods in which a person is contagious and able to spread the resistant strain to others. And because bacteria mutate much more quickly than researchers can develop new antibiotics, the possibility exists that one day highly lethal strains of resistant bacteria will evolve and doctors will have no effective way to treat them.

In recent years, S. typhi has proved resistant to trimethoprim-sulfamethoxazole, ampicillin and tetracycline, in addition to chloramphenicol. In some parts of the world, such as Vietnam and Tajikistan, resistance has begun to extend even to new antibiotics such as ciprofloxacin (Cipro).

In the United States, most doctors now prescribe ciprofloxacin for adults other than pregnant women. Women who are pregnant and children most often receive ceftriaxone (Rocephin) injections. Still, all of these drugs can cause side effects and long-term use can lead to the development of antibiotic-resistant strains of bacteria.

Other treatment steps aimed at managing symptoms include:

• Drinking fluids. This helps prevent the dehydration that results from a prolonged fever and diarrhea. If you're severely dehydrated, you may need to receive fluids through a vein in your arm (intravenously).
• Eating a healthy diet. Nonbulky, high-calorie meals can help replace the nutrients you lose when you're sick.

In many developing nations, the public health goals that can help prevent and control typhoid — safe drinking water, improved sanitation and adequate medical care — may be difficult to achieve. For that reason, some experts believe that vaccinating high-risk populations is the best way to control typhoid fever.

Two vaccines are currently in use — one is injected in a single dose, and the other is administered orally over a period of days. Neither is 100 percent effective, and both require repeat vaccinations. No vaccine exists for paratyphoid fever.

If you're traveling to an area where typhoid fever is endemic, consider being vaccinated. But because the vaccine won't provide complete protection, be sure to follow these guidelines as well:

• Wash your hands. Frequent hand washing is the best way to control infection. Wash your hands thoroughly with hot, soapy water, especially before eating or preparing food and after using the toilet. Carry an alcohol-based hand rub for times when water isn't available.
• Avoid untreated water. Contaminated drinking water is a particular problem in areas where typhoid is endemic. For that reason, drink only bottled water or canned or bottled carbonated beverages, wine and beer. Carbonated bottled water is safer than still water is. Wipe the outside of all bottles and cans before you open them. Ask for drinks without ice. Use bottled water to brush your teeth, and try not to swallow water in the shower.
• Avoid raw fruits and vegetables. Because raw produce may have been washed in unsafe water, avoid fruits and vegetables that you can't peel, especially lettuce. To be absolutely safe, you may want to avoid raw foods entirely.
• Choose hot foods. Avoid food that's stored or served at room temperature. Steaming hot foods are best. And although there's no guarantee that meals served at the finest restaurants are safe, it's best to avoid food from street vendors — it's more likely to be contaminated.

To prevent infecting others
If you're recovering from typhoid or paratyphoid, these measures can help keep others safe:

• Wash your hands often. This is the single most important thing you can do to keep from spreading the infection to others. Use plenty of hot, soapy water and scrub thoroughly for at least 30 seconds, especially before eating and after using the toilet.
• Clean household items daily. Clean toilets, door handles, telephone receivers and taps at least once a day with a household cleaner and paper towels or disposable cloths.
• Avoid handling food. Avoid preparing food for others until your doctor says you're no longer contagious. If you work in the food service industry or a health care facility, you won't be allowed to return to work until tests show that you're no longer shedding typhoid bacteria.
• Keep personal items separate. Set aside towels, bed linen and utensils for your own use and wash them frequently in hot, soapy water. Heavily soiled items can be soaked first in disinfectant.