Symptoms of Shigella Infection
Most people who are infected with Shigella develop diarrhea, fever, and stomach cramps after they are exposed to the bacteria. Symptoms of shigellosis, the illness caused by the ingestion of Shigella bacteria, may start within 12 to 96 hours after exposure, and usually begin within 1 to 3 days (APHA, 2000).
Diarrhea associated with Shigella food poisoning is bloody 25% to 50% of the time and most often contains mucus. The diarrhea may range from mild to very severe diarrhea. Rectal spasms, medically termed “tenesmus,” are common. A severe infection with high fever may be associated with seizures in children less than two years old.
Shigellosis usually resolves in 5 to 7 days.
Some persons who are infected with shigellosis may have no symptoms at all, but may still pass Shigella bacteria to others. Someone who contracts shigellosis through contact with another person is considered a secondary case.
Persons with shigellosis in the U.S. rarely require hospitalization, although the hospitalization rate has been estimated to be in excess of 50,000 per year (Mead, et al., 1999). The hospitalization rate tends to be highest among older individuals (MMWR April 10, 2009).
In the U.S., it is estimated that about 700 persons die yearly from shigellosis (Mead, 1999). Young children and the elderly are at greatest risk of death from a Shigella infection. More than one million deaths occur in the developing world yearly due to infections with Shigella; the victims are mostly children (Philpott, Edgeworth & Sansonetti, 2000).
What are the serious and long-term risks of Shigella infection?
The illness caused by Shigella food poisoning is more severe than other forms of gastroenteritis. Once ingested, Shigella bacteria multiply in the human intestinal tract and invade the cells, which results in much tissue destruction (Philpott, Edgeworth & Sansonetti, 2000). Many strains produce a toxin called Shiga toxin, which is very potent and destructive.
Shiga toxin is very similar to the verotoxin produced by E. coli O157:H7 and other pathogenic strains of E. coli, and Shigella food poisoning can therefore result in hemolytic uremic syndrome, or HUS, which is most often associated with E. coli infections.
Persons with diarrhea caused by S. sonnei in particular usually recover completely, although it may be several months before their bowel habits are entirely normal. About 2% of persons who are infected with S. flexneri later develop pains in their joints, irritation of the eyes, and painful urination. This is called post-infectious arthritis, or reactive arthritis (CDC, 2009a).
Once someone has had shigellosis, they are not likely to be infected with that specific type again for at least several years, but they can still be infected with other types of Shigella.
Complications of Shigella Food Poisoning
Common complications of shigellosis include:
- severe dehydration
- seizures in small children
- rectal bleeding
- invasion of the blood stream by bacteria (bacteremia or sepsis).
Other, more rare and serious complications include:
Proctitis and rectal prolapse. The bacteria that cause shigellosis may also cause inflammation of the lining of the rectum (proctitis) or rectal prolapse. In the latter condition, straining during bowel movements may cause the rectal mucous membrane, or lining, to move down or through the anus (Mayo website, 2009).
Toxic megacolon. This rare complication of shigellosis occurs when the colon becomes paralyzed, preventing bowel movements or passing gas. Signs and symptoms include abdominal pain and swelling, fever, weakness, and disorientation. Untreated, the colon may rupture and cause peritonitis, a life-threatening condition requiring emergency surgery (Mayo clinic, 2009). It is more common in S. dysenteriae infections (APHA, 2000).
Reactive Arthritis. Recent data suggest that the more severe the initial gastrointestinal infection, the more likely reactive arthritis (formerly called Reiter’s Syndrome) will develop (Carter & Hudson, 2009), although it is usually associated with Shigella flexneri infection(APHA, 2000). Up to 3% of persons who are infected with Shigella may later develop joint pain and swelling, irritation of the eyes, and sometimes-painful urination. It occurs because the immune system, intending to fight Shigella, attacks the body instead (Ringrose, 2001).
Reactive arthritis is most common in persons with the HLA-B27 genetic makeup (testing for this is readily available), and is more common in adults than children. Reactive arthritis can last for months or years and may be difficult to treat.
Hemolytic uremic syndrome (HUS). Hemolytic uremic syndrome is a rare complication of shigellosis, that is more commonly caused by E. coli O157:H7. HUS can lead to a low red blood cell count (hemolytic anemia), low platelet count (thrombocytopenia), and acute kidney failure (Mayo Clinic, 2009). It is more common in individuals suffering Shigella dysenteriae infections (APHA, 2000).