Shigella is a group of bacteria that causes an intestinal infection known as shigellosis. This microorganism is a Gram-negative, rod-shaped bacterium, not a virus. Shigellosis is a common cause of diarrheal disease globally, affecting millions each year.
How Shigella Spreads
Shigella bacteria primarily spread through the fecal-oral route, meaning the bacteria transfer from an infected person’s feces to another’s mouth. This occurs through direct contact, such as caring for someone with shigellosis or changing a diaper. Indirect transmission happens when contaminated surfaces, like bathroom fixtures or toys, are touched, and then hands contact the mouth or food.
Contaminated food and water are also common sources of infection. This includes eating food prepared by someone with shigellosis who did not wash their hands, or consuming produce grown in fields exposed to contaminated sewage. Swallowing contaminated recreational water from lakes or rivers can also lead to infection. Only a small number of Shigella bacteria, sometimes as few as 10 to 100 organisms, are needed to cause illness because they survive the stomach’s acidic environment.
Recognizing the Symptoms
Symptoms of shigellosis typically begin one to two days after exposure and can last about seven days. Common signs include watery or loose diarrhea, which may contain mucus, pus, or blood. Individuals may also experience fever, abdominal pain, and cramping.
Another symptom is tenesmus, a painful, persistent urge to pass stool even when bowels are empty. While some people have mild, watery diarrhea, others, particularly young children, can develop more severe symptoms. In young children, symptoms might include sudden fever, irritability, nausea, vomiting, and abdominal distension, with stools becoming bloody, pus-filled, and mucoid within three days.
Diagnosis and Treatment
Diagnosing shigellosis typically involves a physical examination and laboratory testing. A healthcare professional collects a stool sample, analyzed in a lab to identify Shigella bacteria or their toxins. Stool cultures are useful for confirming the diagnosis.
Treatment for shigellosis focuses on supportive care, primarily rehydration therapy, to replace fluids and electrolytes lost due to diarrhea. For mild cases, drinking water may be sufficient. Children and those with significant dehydration may benefit from oral rehydration solutions, which contain necessary salts. In severe instances, intravenous fluid rehydration may be required in a hospital setting. Antibiotics may be prescribed for severe infections or for individuals at higher risk, such as infants, older adults, or those with weakened immune systems. The choice of antibiotic depends on local resistance patterns, as Shigella has shown increasing resistance to some common antibiotics. Anti-diarrhea medicines like loperamide are generally not recommended for shigellosis, as they can worsen the condition.
Preventing Shigella Infection
Preventing shigellosis involves several practical measures, with rigorous handwashing as a primary defense. Hands should be thoroughly washed with soap and clean, running water, especially after using the toilet, changing diapers, and before handling or eating food. If soap and water are unavailable, an alcohol-based hand sanitizer with at least 60% alcohol can be used, though it may be less effective on visibly dirty hands.
Safe food preparation practices are also important. This includes cooking food to appropriate internal temperatures and thoroughly washing raw fruits and vegetables before consumption. Avoiding contaminated water sources, such as untreated recreational water in lakes or pools, helps prevent infection. When traveling to areas with potentially unsafe water or sanitation, drink only treated or boiled water, avoid ice made from tap water, and consume only hot, cooked foods or fruits that can be peeled. Individuals with shigellosis should avoid preparing food for others until they are confirmed to no longer be shedding the bacteria.
Potential Complications
While most people recover from shigellosis without lasting issues, some individuals may experience complications. Dehydration is a common concern due to fluid loss from diarrhea, and in severe cases, it can lead to shock. Young children and chronically ill adults face a higher risk for severe dehydration.
Other potential complications include hemolytic-uremic syndrome (HUS), a rare but serious condition causing kidney failure, a low red blood cell count, and a low platelet count. Reactive arthritis, characterized by joint pain, eye irritation, and painful urination, can develop in about 2% of people infected with Shigella flexneri and may last for months or even years. In rare instances, post-infectious irritable bowel syndrome (IBS) has been observed following shigellosis, with symptoms potentially persisting for several years.