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Shigella

shigella_1.jpgShigella is a bacterium that can cause sudden and severe diarrhea (gastroenteritis) in humans. Shigellosis is the name of the disease that Shigella causes. The illness is also known as “bacillary dysentery.” Shigella bacteria can infect the intestinal tract after the ingestion of relatively few organisms. This is why shigellosis is the most communicable of the bacterial-induced diarrheas.

The source of Shigella bacteria is the excrement (feces) of an infected individual that is ultimately ingested by another person. The infectious material is spread to new cases by person-to-person contact or via contaminated food or water. Approximately 20% of the nearly 450,000 cases of shigellosis that occur annually in the U.S are foodborne-related. Generally, the food preparer is the individual who contaminates the food, but food may also become contaminated during processing. Contamination of drinking water by Shigella is a problem that more often occurs in the developing world, but swimming pools and beaches in the U.S. can become contaminated by infected individuals. No group of individuals is immune to shigellosis, but certain individuals are at increased risk, particularly small children. Persons infected with HIV experience shigellosis much more commonly than other individuals.

Symptoms of Shigella Infection

Most people who are infected with Shigella develop diarrhea, fever, and abdominal cramps. Severity of the disease ranges from mild to very severe diarrhea. Diarrhea is bloody 25-50% of the time and most often contains mucus. Rectal spasms are common. The illness starts 12 hours to 6 days, usually 1 to 2 days, after exposure to the bacteria. Dehydration is also a common symptom.

Detection and treatment of Shigella Infection

A culture of an infected personís stool sample can identify the Shigella bacteria. The laboratory can also do special tests to tell which species of Shigella the person has and which antibiotics would be best to treat it.

Although shigellosis is usually a self-limited illness, antibiotics can shorten the course, and in the most serious cases, might be life-saving. When therapy is indicated, a fluoroquinolone antibiotic is the recommended first-line treatment for non-pregnant adults, such as ciprofloxacin 500 mg twice daily for three days. Alternative antimicrobial agents include trimethoprim-sulfamethoxazole, azithromycin, and ceftriaxone. Antidiarrheal agents such as loperamide (Imodium) or diphenoxylate with atropine (Lomotil) are likely to make the illness worse and should be avoided.

While shigellosis usually resolves in 5 to 7 days, it may be several months before an affected personís bowel habits are entirely normal. In some persons, especially young children, the elderly, and immune compromised persons, the diarrhea can be so severe that the affected person needs to be hospitalized. It is estimated that over 6,000 hospitalizations for shigellosis occur each year in the U.S. Complications of shigellosis include severe dehydration, seizures in small children, rectal bleeding, and invasion of the blood stream by the bacteria. In the U.S., it is estimated that about 70 persons die yearly from shigellosis, with small children and the elderly at greatest risk of dying.

Up to 3% of persons infected with Shigella may later develop a syndrome that includes joint pain and swelling, irritation of the eyes, and sometimes painful urination. This is a reaction to the previous gastroenteritis and is called reactive arthritis or Reiter’s Syndrome. Basically, the immune system, intending to fight Shigella, attacks the bodyís cells. Reiter’s Syndrome is most common in persons with the human leukocyte antigen (HLA) B27 genetic makeup. Reiter’s Syndrome can last for months or years, can lead to chronic arthritis, and may be difficult to treat.

How can a Shigella Infection be Prevented?

Frequent and careful hand washing with soap and water should be done by both the ill individual and anyone who is in contact with that person. Supervised hand washing of all children should be followed in day care centers and as soon as children return home. Young children with a Shigella infection, or with diarrhea of any cause, should not be in contact with uninfected children.

Everyone who changes an infected child’s diapers should be sure the diapers are disposed of properly in a closed-lid garbage can and should wash their hands carefully with soap and warm water immediately after changing the diapers. After use, the diaper changing area should be wiped down with disinfectant, such as household bleach.

Shigella organisms are killed by heat used in cooking. People who have shigellosis or any diarrhea should not prepare food for others until they have been shown to no longer be carrying the bacteria.

At swimming pools, maintaining a chlorine level of at least 0.5-PPM will kill Shigella. Children not yet toilet trained should be excluded from public swimming areas; stay clear if this rule is broken. Children with diarrhea should never be taken to public swimming areas.

Drink water only if it has been chlorinated (most tap water) or treated with ozone (most bottled water). Avoid drinking pool or beach water. Consume only pasteurized dairy products.

Simple precautions taken while traveling to the developing world can also prevent getting shigellosis: “boil it, cook it, peel it, or forget it”. Drink beverages only if they are canned/bottled in a sanitary environment, boiled (like coffee), or have been in contact with alcohol for a prolonged period (wine or beer, not mixed drinks). Do not use ice in beverages.

References

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