The Shigella Outbreak

Screen Shot 2016-07-05 at 5.30.27 PMOn December 4, 2015 staff at the County of San Diego Health and Human Services Agency (SDHHSA) detected an outbreak of Shigella among customers of Café Coyote, a restaurant located in the Old Town district of San Diego. The outbreak was identified through routine interviews with reported case patients. Additional cases were reported by other county/state health jurisdictions and complaints called in to the County of San Diego Department of Environmental Health (DEH).  A total of five separate affected parties ranging in size from 2 to 15 persons with 1 to 8 ill persons in the party were identified. Four of the parties dined at Café Coyote on November 24, 2015. The fifth party dined the morning of November 25. Two parties also ate at the restaurant on another occasion between November 23 and November 26.  Thirty-six persons were interviewed representing all five parties. There were 19 cases and 17 controls. Six ill persons were cultured confirmed with Shigella sonnei. One patient was positive for Shigella by PCR. There were 12 probable cases.

Genetic testing of isolates cultured from three outbreak associated case patients was conducted by the Microbial Diseases Laboratory at the California Department of Public Health (CDPH). Pulsed field gel electrophoresis (PFGE) showed that all three cases were infected with PulseNet strain J16X01.1166.

Case control data analysis showed that salsa was statistically associated with illness.  All of the ill persons consumed salsa versus only 41% of the controls, p. <0.0001. Investigators were not able to determine if there was a contaminated ingredient or if the salsa was contaminated via an ill food handler. DEH conducted an on-site investigation at the Café Coyote on December 7. Salsa was observed to be slightly out of proper temperature holding range. All food handlers including those who prepared salsa denied illness.  Many food handlers participate in serving any one table so any one of the 200 food handlers could have potentially contaminated the salsa.

SDHHSA and CDPH reported the outbreak to the Centers for Disease Control and Prevention (CDC) using the Foodborne Disease Outbreak Report form. The local identification number assigned to the outbreak was 15-244.

The Shigella germ is a family of enteric bacteria that can cause diarrhea in humans. They are microscopic living organisms that thrive in human intestines and are spread through person-to-person contact. Japanese scientist Kiyoshi Shiga, for whom they are named, discovered Shigella over 100 years ago.

Shigellosis, also known as bacillary dysentery, is the infectious disease caused by the Shigella bacteria. Most people who are infected with Shigella develop diarrhea, fever, and stomach cramping that that begins one or two days after exposure—the diarrhea is often bloody. For most people, Shigellosis usually resolves on its own in five-to-seven days. In some persons, though—especially young children and the elderly—the diarrhea can become so severe that the patient needs to be hospitalized. A severe infection with high fever may also be associated with seizures in children younger than two-years-old. Yet other persons who are infected may be carriers but have no symptoms at all, and still pass the Shigella bacteria to others.

There are several different kinds of Shigella bacteria: Shigella sonnei, also known as “Group D,” accounts for much of the infection in the United States and is the strain most often linked to infection from food (shigellosis accounts for less than 10% of the reported outbreaks of foodborne illness in the United States.) A second type, Shigella flexneri, or “group B,” accounts for almost all of the rest of the infections in the U.S., and recent studies have determined that a high percentage of infection by this strain is transmitted sexually. Other types of Shigella, such as Shigella dysenteriae type 1, are most often found in water that is contaminated with human feces. Although rare in the U.S., these other types of Shigella continue to be important causes of death and disease in the developing world.

Shigellosis infections are more common in summer than winter. An estimated 500,000 cases of shigellosis occur annually in the U.S. and Shigella infections cause an estimated 600,000 deaths per year worldwide.[1] Children, especially toddlers between the ages of two and four, are 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. Most of the deaths caused by Shigella infections occur in developing countries with poor hygiene and unsafe water supplies.

Shigella bacteria

Screen Shot 2016-07-05 at 5.30.07 PMIncreasingly, multidrug-resistant shigellosis cases are appearing in the U.S. that are often linked to travelers from outside the US.[2] Multidrug-resistant cases include Shigella sonnei, which is resistant to ciprofloxacin, a main line antibiotic used to treat infections in adults. Shigella is already resistant to ampicillin.  

Where does Shigella come from?

The organism is frequently found in water that is polluted with human feces. Salads (potato, tuna, shrimp, macaroni, and chicken), raw vegetables, dairy products, and poultry are foods commonly listed as sources of Shigella. Therefore, water polluted with human feces, and unsanitary handling by food handlers, are the two most common causes of contamination. The exact number of infections attributable to contaminated food is unknown, but because it takes very little Shigella to cause infection, the number of infections is likely substantial.

How is Shigella detected?

Determining that Shigella is the cause of a person’s illness depends on laboratory tests that identify the bacteria in the stools of the infected person. These tests are sometimes not routinely performed unless the laboratory is instructed specifically to look for the organism. Laboratories can also do special tests to identify the specific type of Shigella the person has become infected with and which antibiotics, if any, would be the best to treat it. Organisms like Shigella are difficult to isolate in foods because standard methods are insensitive to such toxins. Recently, a method to identify foodborne pathogens like Shigella, by specifying segments of the pathogen’s DNA, has been developed by the FDA and is currently under field test. But the isolation procedures are still inadequate.

What are the typical symptoms of Shigella?

Symptoms include abdominal pain, cramps, diarrhea, fever, vomiting, blood, pus, or mucus in stools, and painful rectal spasms. These symptoms normally manifest one to two days after ingestion of the pathogen. The disease is caused when virulent Shigella organisms attach to and penetrate the wall of the intestinal tract. After invasion, they multiply and spread to other smooth surface cells within the body, resulting in tissue destruction. Some strains produce enterotoxin and Shiga toxin, very much like the verotoxin of E. coli O157:H7.

What are the more severe symptoms and long-term risks of Shigella?

Persons with Shigella-related diarrhea usually recover completely, although it may be several months before their bowel habits are entirely normal. But about 3% of persons who are infected with one type of ShigellaShigella flexneri—will later develop pains in their joints, irritation of the eyes, and painful urination. This is called Reiter’s Syndrome. Reiter’s Syndrome can last for months or years, can lead to chronic arthritis, and is difficult to treat. Reiter’s Syndrome is caused by a reaction to Shigella infection that happens only in people who are genetically predisposed to it. Other long-term health risks associated with Shigella infection include reactive arthritis and hemolytic uremic syndrome (HUS).

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. Infants, the elderly, and those with weakened immune systems are susceptible to the severest symptoms of disease, but all humans are susceptible to some degree. Shigellosis is also a very common illness suffered by those with acquired immune deficiency syndrome (AIDS) and other immuno-compromised individuals.


[1]           Id.: “Shigella causes an estimated 500,000 cases of diarrhea in the United States every year. It spreads easily and rapidly from person to person and through contaminated food and recreational water. It can cause watery or bloody diarrhea, abdominal pain, fever, and malaise.”

[2]           See CDC “Multidrug-resistant Shigellosis Spreading in the United States.” April 2, 2015. Web April 23, 2015.