Shigellosis

Overview
Shigellosis, also known as bacillary dysentery in its most severe manifestation, is a foodborne illness caused by infection by bacteria of the genus Shigella. It accounts for less than 10% of the reported outbreaks of foodborne illness in the USA. Shigellosis rarely occurs in animals; it is principally a disease of humans and primates such as monkeys and chimpanzees. The causative organism is frequently found in water polluted with human feces, and is transmitted via the fecal-oral route. The usual mode of transmission is directly person-to-person hand-to-mouth, in the setting of poor hygiene among children.

Epidemiology and Demographics
Approximately 14,000 laboratory confirmed cases of shigellosis and an estimated 448,240 total cases (85% due to S. sonnei) occur in the United States each year. In the developing world, S.flexneri predominates. Epidemics of S. dysenteriae type 1 have occurred in Africa and Central America with case fatality rates of 5-15%.


 * All reported cases are laboratory-confirmed in states or at CDC. Shigellosis is a notifiable infectious disease.
 * Decreasing incidence in cases since 1995; characteristically, S. sonnei causes large periodic outbreaks.

How common is shigellosis?
Every year, about 18,000 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. Shigellosis 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 more 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.

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 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. 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 may look and smell 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. Shigella infections can also be acquired by drinking or swimming in contaminated water. Water may become contaminated if sewage runs into it, or if someone with shigellosis swims in it.

Risk Factors
In the United States, groups at increased risk of shigellosis include children in child-care centers and persons in custodial institutions, where personal hygiene is difficult to maintain; Native Americans; orthodox Jews; international travelers; men who have sex with men; and those in homes with inadequate water for handwashing.

Etiologic Agent:
Four species of Shigella: boydii, dysenteriae, flexneri, and sonnei.

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 the shigellosis in the United States. A second type, Shigella flexneri, or "group B" Shigella, accounts for almost all of 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, causes deadly epidemics there.

How is it transmitted?

 * Food or water contamination
 * Person to person spread (small number of organisms needed)
 * Incubation period is 1-7 days

Genetics
Reiter's syndrome is a late complication of S. flexneri infection, especially in persons with the genetic marker HLA-B27.

Diagnosis
Many different kinds of diseases can cause diarrhea and bloody diarrhea, and the treatment depends on which germ is causing the diarrhea. Determining that Shigella is the cause of the illness depends on laboratory tests that identify Shigella in the stools of an infected person. These tests are sometimes not performed unless the laboratory is instructed specifically to look for the organism. The laboratory can also do special tests to tell which type of Shigella the person has and which antibiotics, if any, would be best to treat it.

Symptoms
Symptoms may range from mild abdominal discomfort to full-blown dysentery characterized by cramps, diarrhea, fever, vomiting, blood, pus, or mucus in stools or tenesmus. Onset time is 12 to 50 hours.

Infections are associated mucosal ulceration, rectal bleeding, drastic dehydration; fatality may be as high as 10-15% with some strains. Reiter's disease, reactive arthritis, and hemolytic uremic syndrome are possible sequelae that have been reported in the aftermath of shigellosis.

In some persons, especially young children and the elderly, the diarrhea can be so severe that the patient needs to be hospitalized. A severe infection with high fever may also 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.

Clinical Features

 * Symptoms
 * Fever (40%)
 * Bloody Diarrhea (40-50%)
 * Vomiting (35%)
 * Abdominal Pain (90%)
 * Mucoid Diarrhea (70-80%)
 * Constitutional symptoms often precede diarrhea
 * Small volume diarrhea (dehydration is unusual)
 * Intestinal Complications (Rare)
 * Rectal prolapse, proctitis
 * Toxic Megacolon
 * Colonic Perforation
 * Systemic Complications
 * Bacteremia (gram-negative rod's (GNR’s), not just Shigella)
 * Hyponatremia (syndrome of inappropriate antidiuretic hormone secretion (SIADH)
 * Leukemoid Reactions
 * Seizure
 * Reactive Arthritis
 * Hemolytic Uremic Syndrome
 * MAHA (microangiopathic hemolytic anemia)
 * Thrombocytopenia
 * Acute Renal Failure

Risk Stratification and Prognosis
Reiter's syndrome is a late complication of S. flexneri infection, especially in persons with the genetic marker HLA-B27. Hemolytic-uremic syndrome can occur after S. dysenteriae type 1 infection. Convulsions may occur in children; the mechanism may be related to a rapid rate of temperature elevation or metabolic alterations

Treatment of Shigellosis
Treatment consists mainly of replacing fluids and salts lost because of diarrhea. Oral replacement is satisfactory for most people, but some may need to receive fluids intravenously. In most cases, the disease resolves within 4 to 8 days without antibiotics. Severe infections may last 3 to 6 weeks. Antibiotics such as trimethoprim-sulfamethoxazole, norfloxacin, ciprofloxacin, or furazolidone may be given when the person is very young or very old, when the disease is severe, or when there is a high risk of the infection spreading to other people. The severity of the symptoms and the length of time the stool contains Shigella are reduced with antibiotics. Antidiarrheal drugs (such as diphenoxylate or loperamide) may prolong the infection and should not be used.

Primary Prevention
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. Frequent, supervised handwashing of all children should be followed in day care centers and in homes with children who are not completely toilet-trained (including children in diapers). When possible, young children with a Shigella infection who are still in diapers should not be in contact with uninfected children.

People who have shigellosis should not prepare food or pour water for others until they have been shown to no longer be carrying the Shigella bacterium.

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 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 household bleach, Lysol or bactericidal wipes.

Basic food safety precautions and regular drinking water treatment prevents shigellosis. At swimming beaches, having enough bathrooms near the swimming area helps keep the water from becoming contaminated.

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

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.
 * Persons with diarrheal illness should not prepare food for others.
 * Avoid drinking pool water

Secondary Prevention
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 and compared to other Shigella. If many cases occur at the same time, it may mean that a restaurant, food or water supply has a problem which 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 hygiene for vegetables and fruit picking and packing may prevent shigellosis caused by contaminated produce.

Some prevention steps occur everyday, without you thinking about it. Making municipal water supplies safe and treating sewage are highly effective prevention measures that have been in place for many years.

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 to investigate outbreaks, determine means of transmission and devise control measures. 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.

Histopathology of Shigellosis (Bacillary dysentery)


Acknowledgements
The content on this page was first contributed by: C. Michael Gibson, M.S., M.D.