1. Organism

Shigella are Gram-negative, non-motile, non- sporeforming, rod-shaped bacteria. Shigella species, which include Shigella sonnei, S. boydii, S. flexneri, and

S. dysenteriae, are highly infectious agents. Some strains produce enterotoxins and Shiga toxin. The latter is very similar to the toxins produced by E. coli O157:H7.

Humans are the only host of Shigella, but it has also been isolated from higher primates. The organism is frequently found in water polluted with human feces.

In terms of survival, shigellae are very sensitive to environmental conditions and die rapidly. They are heat sensitive and do not survive pasteurization and cooking temperatures. In terms of growth, shigellae are not particularly fastidious in their requirements and, in most cases, the organisms are routinely cultivated in the laboratory, on artificial media. However, as noted in subsequent sections, the relative difficulty of cultivating this organism is dependent, in part, on the amount of time within which stool or food samples are collected and processed.

Shigella species are tolerant to low pH and are
able to transit the harsh environment of the
stomach. These pathogens are able to survive
and, in some cases, grow in foods with low pH,
such as some fruits and vegetables. They are
able to survive on produce commodities
packaged under vacuum or modified
atmosphere and can also survive in water, with a slight decrease in numbers.

2. Disease

The illness caused by Shigella is shigellosis (also called bacillary dysentery), in which diarrhea may range from watery stool to severe, life-threatening dysentery. All Shigella spp. can cause acute, bloody diarrhea. Shigella spp. can spread rapidly through a population, particularly in crowded and unsanitary conditions.

S. dysenteriae type 1 causes the most severe disease and is the only serotype that produces the Shiga toxin, which may be partially responsible for cases in which hemolytic uremic syndrome (HUS) develops. S. sonnei produces the mildest form of shigellosis; usually watery diarrhea.

S. flexneri and S. boydii infections can be either mild or severe.
In developed countries, S. sonnei is the Shigella species most often isolated, whereas S. flexneri predominates in developing countries.

• Mortality: In otherwise healthy people, the disease usually is self-limiting, although some strains are associated with fatality rates as high as 10-15%. (See Illness / complications section, below.)

• Infective dose: As few as 10 to 200 cells can cause disease, depending on the age and condition of the host.

• Onset: Eight to 50 hours.

• Illness / complications: In otherwise healthy people, the disease usually consists of self- limiting diarrhea (often bloody), fever, and stomach cramps. Severe cases, which tend to occur primarily in immunocompromised or elderly people and young children, are associated with mucosal ulceration, rectal bleeding, and potentially drastic dehydration. Potential sequelae of shigellosis include reactive arthritis and hemolytic uremic syndrome.

• Symptoms: May include abdominal pain; cramps; diarrhea; fever; vomiting; blood, pus, or mucus in stools; tenesmus (straining during bowel movements).

• Duration: Uncomplicated cases usually resolve in 5 to 7 days. Most of the time, the illness is self-limiting. In some circumstances, antibiotics are given; usually trimethoprim-sulfamethoxazole, ceftriaxone, or ciprofloxacin.

• Route of entry: The fecal-oral route is the primary means of human-to-human transmission of Shigella. With regard to foods, contamination is often due to an infected food handler with poor personal hygiene.

• Pathway: The disease is caused when Shigella cells attach to, and penetrate, colonic epithelial cells of the intestinal mucosa. After invasion, they multiply intracellularly and spread to contiguous epithelial cells, resulting in tissue destruction. As noted, some strains produce enterotoxin and Shiga toxin similar to those produced by E. coli O157:H7.

3. Frequency

A recent Centers for Disease Control and Prevention (CDC) report on foodborne illnesses acquired annually in the United States revealed that about 15,000 laboratory-confirmed isolates are reported each year, with estimates of actual occurrence ranging from 24,511 to 374,789 cases (average of 131,243). About 31% of these are estimated to be foodborne. Estimates of foodborne illness episodes (mean) caused by 31 pathogens placed Shigella as the sixth most frequent cause (after norovirus, Salmonella species, Clostridium perfringens, Campylobacter, and Staphylococcus aureus, in that order).

Episodes of shigellosis appear to follow seasonal variations. In developed countries, the highest incidences generally occur during the warmer months of the year.

4. Sources

Most cases of shigellosis are caused by ingestion of fecally contaminated food or water. In the case of food, the major factor for contamination often is poor personal hygiene among food handlers. From infected carriers, this pathogen can spread by several routes, including food, fingers, feces, flies, and fomites.

Shigella is commonly transmitted by foods consumed raw; for example, lettuce, or as non- processed ingredients, such as those in a five-layer bean dip. Salads (potato, tuna, shrimp, macaroni, and chicken), milk and dairy products, and poultry also are among the foods that have been associated with shigellosis.

5. Diagnosis

Diagnosis is by serological or molecular identification of cultures isolated from stool. Shigella may be more difficult to cultivate if stool samples are not processed within a few hours.

6. Target Populations

All people are susceptible to shigellosis, to some degree, but children 1 to 4 years old, the elderly, and the immunocompromised are most at risk. Shigellosis is very common among people with AIDS and AIDS-related complex.

7. Food Analysis

Shigellae remain a challenge to isolate from foods. A molecular-based method (PCR) that targets a multi-copy virulence gene has been developed and implemented by FDA. Improvements in the bacterial isolation method continue and should be available in the near future.

The window for collecting and processing Shigella from foods, for cultivation, may be days (rather than hours, as is the case with stool), depending on the food matrix and storage conditions; e.g., temperature. Shigella species can be outgrown by the resident bacterial populations found in foods, which may reflect the usual low numbers of the organism present in foods and, in some foods, a very large number of non-Shigella bacteria. Another factor that reduces the chance of isolating Shigella from foods may be the physiological state of the pathogen at the time of analysis. Environmental conditions could affect its ability to either grow or survive in any food matrix.

8. Examples of Outbreaks

The CDC’s Morbidity and Mortality Weekly Reports provide information about Shigella outbreaks.

9. Other Resources

• Loci index for genome Shigella spp.

• GenBank Taxonomy database

• More information about Shigella and shigellosis can be found on the CDC website.

Lanza said the county usually sees three to 30 cases of Shigella a month, and this month there have been about 12 to 15 cases.

"We're seeing this in child-care centers, and that's where our most-vulnerable population center is — our children — and we just want child-care providers and parents to know what to look for," Lanza said.

He said simple hygiene practices can keep gastrointestinal illnesses like Shigella at bay.

"The No. 1 way of transmitting these kind of diseases is by not washing your hands with soap and water," Lanza said. He said it's important to thoroughly wash hands after using the bathroom, changing diapers and handling food.

Lanza had another health message: If you or your child has a gastrointestinal illness, stay home instead of spreading the germs.

"If you as an adult, or your child, are sick, for at least 48 hours, stay at home. Don't go to work," he said.

Small children acquire Shigella at the highest rate.

Prevent the spread of Shigella from an infected person to others with frequent and careful handwashing with soap.

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 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 outbreaks of 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 Shigella bacteria, 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.

When traveling in developing countries, only treated or boiled water, and eat only cooked hot foods or fruits you peel yourself.

School district spokesman Kevin Christian said the bacteria were not found at the school. But since both cases involved Maplewood students, officials decided to clean the school for the safety of the students. It sent a team of custodians to scrub the school and cafeteria just in case the bacteria originated there.

Christian said the illness is more common in the day-care setting.

The school district also sent an Alert Now message and a letter to Maplewood parents.

Superintendent of Schools Jim Yancey said the district does not know who the children are since, by law, the Health Department could not disclose those names.

Yancey said the district response was phenomenal. He said he was worried because of the profoundly disabled young students at the school. He wanted to make sure the bacteria, if any, was eliminated quickly.

"It sounds like they did a good job," said School Board Chairwoman Judi Zanetti.

Yancey said health officials say only 14,000 shigellosis cases are reported annually in the United States.

The 13-year study, involved a review of dairy product outbreaks from 1993 to 2006 in all 50 states. The authors compared the amount of milk produced in the United States during the study period (about 2.7 trillion pounds) to the amount that CDC estimates was likely consumed raw (1 percent or 27 billion pounds) to determine the 150 times higher rate for outbreaks caused by raw milk products. Raw milk products include cheese and yogurt.

The study included 121 dairy–related disease outbreaks, which caused 4,413 illnesses, 239 hospitalizations and three deaths. In 60 percent of the outbreaks (73 outbreaks) state health officials determined raw milk products were the cause. Nearly all of the hospitalizations (200 of 239) were in those sickened in the raw milk outbreaks. These dairy-related outbreaks occurred in 30 states, and 75 percent (55 outbreaks) of the raw milk outbreaks occurred in the 21 states where it was legal to sell raw milk products at the time. The study also reported that seven states changed their laws during the study period.

For a consumer, it is impossible to tell if raw milk is safe to drink by simply looking at, smelling, or tasting it. Even under ideal conditions of cleanliness, the process of collecting milk introduces some bacteria. Unless the milk is pasteurized, these bacteria can multiply and grow in the milk and cause illness in those who consume it. Pasteurization involves heating milk to kill disease-causing bacteria.

“This study shows an association between state laws and the number of outbreaks and illnesses from raw milk products,” said Robert Tauxe, M.D., M.P.H., deputy director of CDC’s Division of Foodborne, Waterborne and Environmental Diseases (DFWED). “Restricting the sale of raw milk products is likely to reduce the number of outbreaks and can help keep people healthier. The states that allow sale of raw milk will probably continue to see outbreaks in the future.”

The study also found that the raw milk product outbreaks led to much more severe illnesses, and disproportionately affected people under age 20. In the raw milk outbreaks with known age breakdowns, 60 percent of patients were younger than age 20, compared to 23 percent in outbreaks from pasteurized products. Because of their underdeveloped immune systems, children are more likely than adults to get seriously ill from the bacteria in raw milk.

“While some people think that raw milk has more health benefits than pasteurized milk, this study shows that raw milk has great risks, especially for children, who experience more severe illnesses if they get sick,” said study co-author Barbara Mahon, M.D., M.P.H., deputy chief of CDC’s DFWED Enteric Diseases Epidemiology Branch. “Parents who have lived through the experience of watching their child fight for their life after drinking raw milk now say that it’s just not worth the risk.”

Additional information on evidence-based scientific studies covering the benefits and risks of raw milk consumption can be found HERE (pdf).

Improper sanitation and cross-contamination can be contributing factors to Shigella outbreaks associated with restaurant food.

The introduction of pasteurization greatly reduced the number of foodborne illness outbreaks associated with milk and other dairy sources, but the consumption of raw milk and unpasteurized cheeses remains a risk factor for Shigella infection. Shigella and other pathogens are shed in the feces of livestock such as cows and goats and can contaminate milk during the milking process.

Fresh fruits and vegetables can become contaminated before or after harvest. Water intended for recreation (e.g., pools, shallow lakes) and for human consumption can also become contaminated. When lakes become contaminated it may be several weeks or months before water quality conditions to improve or return to normal. Proper chlorination kills Shigella bacteria in pools and municipal water systems.

Person-to-person transmission of Shigella occurs through a fecal-oral route, and is particularly common among infants and young children due to their unrefined hygienic practices. Person-to-person transmission of Shigella has also been known to occur between infected individuals and their caregivers, and between infected food handlers and people who consume the food they prepare.

That’s the highest number in any week so far during the current outbreak, which has seen 84 confirmed cases in 13 weeks.

Shigellosis is a highly-contagious diarrhea illness caused by Shigella bacteria. Symptoms include watery or loose stools for several days, and in severe cases abrupt onset of fever, nausea, abdominal cramping and vomiting.

For the past five years, Louisville has had an average of 62 confirmed cases annually.

To prevent the illness, health officials are urging people to wash their hands carefully with soap and water, including under the fingernails. This is especially important after handling items such as diapers, after each bowel movement, after helping children use the toilet and before preparing or eating food, health officials said.

Shigella belongs to a family of bacteria that can cause sudden and severe diarrhea in humans. Shigellosis, the illness caused by the ingestion of Shigella bacteria, is also known as bacillary dysentery. Shigella thrives in the human intestine and is commonly spread both through food and person-to-person contact. Shigella is the third most common pathogen transmitted through food.

Jacksonville NBC affiliate First Coast News reports:

Duval County health leaders say kids are very vulnerable to the infection. Seventy-four percent of cases here have been people between the 0-and-19 age range.

"It's harder to get kids to wash their hands properly and certainly the little kids like two to four year olds, you have to watch them wash their hands because they're still learning to wash their hands and so you just really have to encourage that good behavior," said Karen Elliott, surveillance epidemiologist with the Duval County Health Department.

Each year, New York City has between 300 and 400 cases of the disease, which frequently crops up in day care centers and other places where children congregate. The majority of those affected in this latest outbreak were also children.

No one has been hospitalized, city health department officials said.  The health department has asked doctors not to use antibiotics to treat shigella because drug-resistant strains of the bacteria may be starting to spread.

In any event, a large Shigella outbreak has occurred at Honea Path Elementary School in South Carolina.  Dozens of students have fallen ill in the past several weeks, causing the principal of Honea Path Elementary School to send a letter home to parents explaining what Shigella is and the importance of good handwashing. 

Officials with the State Department of Health and Environmental Control have assisted in the investigation of this outbreak, and have encouraged the school and staff, as well as parents, to recognize the ease by which Shigella can be transmitted person-to-person, and the resulting importance of good handwashing. 

See www.shigellalitigation.com

Shigella is a family of bacteria that can cause sudden and severe diarrhea (gastroenteritis) in humans. Shigellosis – the illness caused by the ingestion of Shigella bacteria – is also known as bacillary dysentery. It can occur after ingestion of fewer than 100 bacteria, making Shigella one of the most communicable and severe forms of the bacterial-induced diarrheas.

Shigella thrives in the human intestine and is commonly spread both through food and by person-to-person contact. Most Shigella infections are passed through the fecal-oral route. This happens when basic hygiene and handwashing habits are inadequate and can happen during certain types of sexual activity. Transmission 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.

Food may become contaminated by infected food handlers who don’t 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 goes into it or if someone with shigellosis swims in or plays with the water (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.

The number of shigellosis cases reported annually to the Centers for Disease Control and Prevention (CDC) has varied over the past several years, from more than 17,000 during 1978–2003, to an all-time low of 14,000 in 2004, to almost 20,000 in 2007. Many cases go undiagnosed and/or unreported, however. The CDC estimates that 450,000 total cases of shigellosis occur in the U.S. every year.

Shigella is the third most common pathogen transmitted through food. During 2006, a total of 1,270 foodborne-related outbreaks from 48 states in the U.S. were reported. Although Shigella was responsible for only 10 (1%) of those outbreaks, 183 confirmed cases of shigellosis were reported. This contrasts with an average of 659 cases annually in the previous five years. Shigella has also responsible for a substantial portion of foodborne outbreaks on cruise ships.

The number of infections and incidence per 100,000 population were reported as follows:

• Salmonella (7,444; 16.20),
• Campylobacter (5,825; 12.68),
• Shigella (3,029; 6.59),
• Cryptosporidium (1,036; 2.25),
• STEC O157 (513; 1.12),
• STEC non-O157 (205; 0.45),
• Yersinia (164; 0.36),
• Listeria (135; 0.29),
• Vibrio (131; 0.29),
• and Cyclospora (17; 0.04).

See the chart below for details. Go here for details on the study.

• Filiberto’s Shigella Outbreak
• Gate Gourmet Shigella Outbreak
• Royal Fork Shigella Outbreak
• Senor Felix Shigella Outbreak
• Shipley Sales Cantaloupe Salmonella Outbreak
• Viva Mexico Shigella Outbreak

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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, but this may largely be due to an increased risk among men having sex with men.

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 ìreactive arthritisî or Reiter's Syndrome. Basically, the immune system, intending to fight Shigella, attacks the bodyís cells. Reiterís Syndrome is most common in persons with the human leukocyte antigen (HLA) B27 genetic makeup. Reiterís Syndrome can last for months or years, can lead to chronic arthritis, and may be difficult to treat. See the Marler Clark sponsored site on Reiterís Syndrome for more information.

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.