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Shigellosis

General Information

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What is shigellosis?

Shigellosis is an infectious disease caused by a group of bacteria called Shigella. Most who are infected with Shigella develop diarrhea, fever, and stomach cramps starting a day or two after they are exposed to the bacteria. The diarrhea is often bloody. Shigellosis usually resolves in 5 to 7 days. Persons with shigellosis in the United States rarely require hospitalization. A severe infection with high fever may be associated with seizures in children less than 2 years old. Some persons who are infected may have no symptoms at all, but may still pass the Shigella bacteria to others.

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What sort of germ is Shigella?

The Shigella germ is actually a family of bacteria that can cause diarrhea in humans. They are microscopic living creatures that pass from person to person. Shigella were discovered over 100 years ago by a Japanese scientist named Shiga, for whom they are named. There are several different kinds of Shigella bacteria: Shigella sonnei, also known as "Group D" Shigella, accounts for over two-thirds of shigellosis in the United States. Shigella flexneri, or "group B" Shigella, accounts for almost all the rest. Other types of Shigella are rare in this country, though they continue to be important causes of disease in the developing world. One type found in the developing world, Shigella dysenteriae type 1, can cause deadly epidemics.

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How can Shigella infections be diagnosed?

Many different kinds of germs can cause diarrhea, so establishing the cause will help guide treatment. Determining that Shigella is the cause of the illness depends on laboratory tests that identify Shigella in the stools of an infected person. The laboratory can also do special tests to determine which antibiotics, if any, would be best to treat the infection.

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How can Shigella infections be treated?

Persons with mild infections usually recover quickly without antibiotic treatment. However, appropriate antibiotic treatment may shorten the duration of illness and decrease the spread of infection. Antibiotic treatment is recommended for patients with severe disease, bloody diarrhea, or compromised immune systems. Resistance to traditional first-line drugs like ampicillin and trimethoprim-sulfamethoxazole is common, and resistance to some other antibiotics is increasing. With this in mind, antibiotic susceptibility testing can help guide appropriate therapy. When susceptibility is unknown or when an ampicillin- or trimethroprim-sulfamethoxazole-resistant strain is isolated, choices for therapy include fluoroquinolones, ceftriaxone, and azithromycin. Antidiarrheal agents such as loperamide (Imodium®) or diphenoxylate with atropine (Lomotil®) can make the illness worse and should be avoided.

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Are there long term consequences to a Shigella infection?

Persons with diarrhea usually recover completely, although it may be several months before their bowel habits are entirely normal. About 2% of persons who are infected with one type of Shigella, Shigella flexneri, later develop pains in their joints, irritation of the eyes, and painful urination. This is called post-infectious arthritis. It can last for months or years, and can lead to chronic arthritis. Post-infectious arthritis is caused by a reaction to Shigella infection that happens only in people who are genetically predisposed to it.

Once someone has had shigellosis, they are not likely to get infected with that specific type again for at least several years. However, they can still get infected with other types of Shigella.

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How do people catch Shigella?

The Shigella bacteria pass from one infected person to the next. Shigella are present in the diarrheal stools of infected persons while they are sick and for up to a week or two afterwards. Most Shigella infections are the result of the bacterium passing from stools or soiled fingers of one person to the mouth of another person. This happens when basic hygiene and handwashing habits are inadequate and can happen during certain types of sexual activity. It is particularly likely to occur among toddlers who are not fully toilet-trained. Family members and playmates of such children are at high risk of becoming infected.

Shigella infections may be acquired from eating contaminated food. Contaminated food usually looks and smells normal. Food may become contaminated by infected food handlers who forget to wash their hands with soap after using the bathroom. Vegetables can become contaminated if they are harvested from a field with sewage in it. Flies can breed in infected feces and then contaminate food. Water may become contaminated with Shigella bacteria if sewage runs into it, or if someone with shigellosis swims in or plays with it (especially in splash tables, untreated wading pools, or shallow play fountains used by daycare centers). Shigella infections can then be acquired by drinking, swimming in, or playing with the contaminated water. Outbreaks of shigellosis have also occurred among men who have sex with men.

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What can a person do to prevent this illness?

Currently, there is no vaccine to prevent shigellosis. However, the spread of Shigella from an infected person to other persons can be stopped by frequent and careful handwashing with soap. Frequent and careful handwashing is important among all age groups. Handwashing among children should be frequent and supervised by an adult in daycare centers and homes with children who have not been fully toilet trained.

If a child in diapers has shigellosis, everyone who changes the child's diapers should be sure the diapers are disposed of properly in a closed-lid garbage can, and should wash his or her hands and the child’s hands carefully with soap and warm water immediately after changing the diapers. After use, the diaper changing area should be wiped down with a disinfectant such as diluted household bleach, Lysol* or bactericidal wipes. When possible, young children with a Shigella infection who are still in diapers should not be in contact with uninfected children.

Basic food safety precautions and disinfection of drinking water prevents shigellosis from food and water. However, people with shigellosis should not prepare food or drinks for others until they have been shown to no longer be carrying the Shigella bacterium, or if they have had no diarrhea for at least 2 days. At swimming beaches, having enough bathrooms and handwashing stations with soap near the swimming area helps keep the water from becoming contaminated. Daycare centers should not provide water play areas.

Simple precautions taken while traveling to the developing world can prevent shigellosis. Drink only treated or boiled water, and eat only cooked hot foods or fruits you peel yourself. The same precautions prevent other types of traveler's diarrhea.

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How common is shigellosis?

Every year, about 14,000 cases of shigellosis are reported in the United States. Because many milder cases are not diagnosed or reported, the actual number of infections may be twenty times greater. Shigellosis is particularly common and causes recurrent problems in settings where hygiene is poor and can sometimes sweep through entire communities. It is more common in summer than winter. Children, especially toddlers aged 2 to 4, are the most likely to get shigellosis. Many cases are related to the spread of illness in child-care settings, and many are the result of the spread of the illness in families with small children.

In the developing world, shigellosis is far more common and is present in most communities most of the time.

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What else can be done to prevent shigellosis?

It is important for the public health department to know about cases of shigellosis. It is important for clinical laboratories to send isolates of Shigella to the City, County or State Public Health Laboratory so the specific type can be determined. If many cases occur at the same time, it may mean that a restaurant, food or water supply has a problem that needs correction by the public health department. If a number of cases occur in a day-care center, the public health department may need to coordinate efforts to improve handwashing among the staff, children, and their families. When a community-wide outbreak occurs, a community-wide approach to promote handwashing and basic hygiene among children can stop the outbreak. Improvements in worker hygiene during vegetable and fruit picking and packing may prevent shigellosis caused by contaminated produce.

Some prevention measures in place in most communities help to prevent shigellosis. Making municipal water supplies safe and treating sewage are highly effective prevention measures that have been in place for many years.

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What is the government doing about shigellosis?

The Centers for Disease Control and Prevention (CDC) monitors the frequency of Shigella infections in the country, and assists local and State health departments in investigating outbreaks, determining means of transmission, and devising control measures. In addition, CDC tracks changes in antibiotic resistance among Shigella through the National Antimicrobial Resistance Monitoring System (NARMS). CDC also conducts research to better understand how to identify and treat shigellosis. The Food and Drug Administration inspects imported foods, and promotes better food preparation techniques in restaurants and food processing plants. The Environmental Protection Agency regulates and monitors the safety of our drinking water supplies. The government has also maintained active research into the development of a Shigella vaccine.

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How can I learn more about this and other public health problems?

You can discuss any medical concerns you may have with your heath care provider. Your local city or county health department can provide more information about this and other public health problems. General information about the public health of the nation is published every week in the "Morbidity and Mortality Weekly Report" by CDC. Epidemiologists in your local and State Health Departments track many important public health problems, investigate special problems that arise, and help prevent them form occurring.

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Some tips for preventing the spread of shigellosis:

  • Wash hands with soap carefully and frequently, especially after going to the bathroom, after changing diapers, and before preparing foods or beverages.
  • Dispose of soiled diapers properly
  • Disinfect diaper changing areas after using them.
  • Keep children with diarrhea out of child care settings.
  • Supervise handwashing of toddlers and small children after they use the toilet.
  • Do not prepare food for others while ill with diarrhea
  • Avoid swallowing water from ponds, lakes, or untreated pools. (See more information about this.)

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