Shigellosis: Symptoms, Causes & Treatment of Dysentery

What Is Shigellosis?

Shigellosis is a bacterial intestinal infection caused by Shigella bacteria that invade and damage the lining of the large intestine. It causes bloody diarrhea, mucus in stool, severe abdominal pain, and fever. Also known as bacillary dysentery, it is one of the most common causes of bloody diarrhea worldwide.

Shigellosis, commonly called bacillary dysentery, is an acute intestinal infection that affects approximately 165 million people globally each year, causing an estimated 600,000 deaths. Unlike many other gastrointestinal infections that primarily affect the small intestine, Shigella bacteria specifically target the large intestine (colon), where they invade the intestinal lining and cause intense inflammation.

The Shigella bacteria belong to the family Enterobacteriaceae and are closely related to E. coli. There are four main species of Shigella that cause human disease: Shigella dysenteriae (the most severe, capable of producing Shiga toxin), Shigella flexneri (most common in developing countries), Shigella boydii (relatively rare), and Shigella sonnei (most common in industrialized countries). Each species has multiple serotypes, and infection with one type does not provide immunity against others.

What makes shigellosis particularly dangerous is its extremely low infectious dose. While most bacterial infections require ingestion of millions of bacteria to cause disease, Shigella can cause infection with as few as 10-100 organisms. This makes it highly contagious and explains why it spreads so easily in settings with poor sanitation, crowded conditions, or inadequate handwashing practices.

The pathophysiology of Shigella infection

When Shigella bacteria are ingested, they survive passage through the acidic environment of the stomach and reach the large intestine. Unlike bacteria that remain in the intestinal lumen, Shigella actively invades the epithelial cells lining the colon. The bacteria enter these cells, multiply within them, and then spread to adjacent cells, destroying the intestinal lining in the process.

This invasive mechanism triggers a powerful inflammatory response. The body's immune system sends white blood cells to fight the infection, resulting in the characteristic symptoms of dysentery: bloody diarrhea containing mucus and pus, intense abdominal cramping, and the painful urge to defecate (tenesmus). The inflammation also causes fever and general malaise as the body attempts to combat the infection.

Some strains, particularly Shigella dysenteriae type 1, produce a potent toxin called Shiga toxin. This toxin can cause additional damage to blood vessels and may lead to serious complications such as hemolytic uremic syndrome (HUS), which affects the kidneys and blood clotting system.

What Are the Symptoms of Shigellosis?

The main symptoms of shigellosis include watery diarrhea that becomes bloody with mucus, severe abdominal cramps, fever (often above 38.5°C/101.3°F), nausea, and tenesmus (painful urge to defecate). Symptoms typically appear 1-3 days after infection and can range from mild to severe.

Shigellosis symptoms typically develop within 1 to 3 days after exposure to the bacteria, though the incubation period can extend up to 7 days in some cases. The severity of symptoms varies considerably depending on the Shigella species involved, the amount of bacteria ingested, and the individual's immune status and overall health.

The infection often begins with general symptoms such as fever, fatigue, and loss of appetite. Within the first 24-48 hours, watery diarrhea develops, which may initially be mistaken for ordinary gastroenteritis. However, as the bacteria invade the intestinal lining, the characteristic symptoms of dysentery emerge: the stool becomes bloody and contains visible mucus or pus, distinguishing shigellosis from many other causes of diarrhea.

Abdominal pain in shigellosis is notably severe and crampy, often described as colicky pain that comes in waves. The pain is typically concentrated in the lower abdomen, corresponding to the location of the large intestine where the infection is centered. Many patients also experience tenesmus, a painful and persistent urge to defecate even when the bowels are empty. This symptom can be extremely distressing and exhausting.

Symptom progression and severity

The disease typically follows a predictable course. During the first 1-2 days, patients experience fever, malaise, and the onset of diarrhea. The diarrhea frequency increases, with patients passing 10-30 watery stools per day in severe cases. By days 2-3, the stools become smaller in volume but more frequent, containing blood and mucus, indicating the invasive phase of the infection.

In uncomplicated cases, symptoms begin to improve after 5-7 days, with most people recovering fully within 1-2 weeks. However, some individuals may continue to shed bacteria in their stool for up to 4 weeks after symptoms resolve, remaining potentially infectious during this period.

Symptoms in children

Children, particularly those under 5 years of age, are at highest risk for severe shigellosis. They may develop symptoms more rapidly and have a higher risk of complications. In addition to the typical symptoms, children may experience fever-induced seizures (febrile seizures), which can be frightening for parents but usually do not cause lasting harm.

Young children also become dehydrated more quickly than adults because of their smaller body size and higher metabolic rate. Signs of dehydration in children include decreased urination, dry mouth and tongue, crying without tears, irritability, and lethargy. Any child with bloody diarrhea should be evaluated by a healthcare provider promptly.

What Causes Shigellosis and How Does It Spread?

Shigellosis is caused by Shigella bacteria and spreads through the fecal-oral route. Transmission occurs through contaminated food or water, direct person-to-person contact, and contaminated surfaces. Only 10-100 bacteria are needed for infection, making it highly contagious.

Shigellosis is caused exclusively by bacteria of the genus Shigella. Understanding how these bacteria spread is essential for prevention. The infection follows the fecal-oral transmission route, meaning the bacteria present in an infected person's stool must somehow be ingested by another person to cause disease.

The extremely low infectious dose of Shigella makes transmission remarkably efficient. While Salmonella infection typically requires ingestion of millions of bacteria, Shigella can establish infection with just 10-100 organisms. This explains why shigellosis outbreaks can spread rapidly through households, daycare centers, nursing homes, and communities with inadequate sanitation.

Primary transmission routes

Contaminated food and water: This is the most common route of transmission globally. Food can become contaminated when handled by an infected person who has not washed their hands properly after using the toilet. Raw vegetables irrigated with contaminated water, shellfish harvested from polluted waters, and food prepared in unsanitary conditions are common sources. In developing countries, contaminated drinking water is a major source of infection.

Person-to-person contact: Direct transmission occurs when bacteria from an infected person's hands are transferred to another person and subsequently to their mouth. This is particularly common in settings involving close contact, such as households with young children, daycare centers, and healthcare facilities. Sexual transmission can also occur, particularly through oral-anal contact.

Contaminated surfaces: Shigella can survive on surfaces for extended periods, especially in moist environments. Touching contaminated surfaces such as bathroom fixtures, doorknobs, diaper-changing stations, or toys and then touching the mouth can lead to infection. This fomite transmission is a significant factor in daycare and household outbreaks.

Risk factors for shigellosis

Several factors increase the risk of acquiring shigellosis:

• International travel: Travelers to regions with poor sanitation infrastructure, particularly parts of Africa, Asia, and Central and South America, face significantly elevated risk. Shigellosis is one of the leading causes of travelers' diarrhea.
• Young age: Children between 1 and 4 years old have the highest incidence of shigellosis. Their developing immune systems, tendency to put objects in their mouths, and incomplete toilet training contribute to their vulnerability.
• Living in crowded conditions: Refugee camps, military barracks, dormitories, and other crowded living situations facilitate rapid spread of the infection.
• Poor sanitation: Lack of access to clean water and adequate toilet facilities dramatically increases transmission risk.
• Immunocompromised status: People with weakened immune systems, including those with HIV/AIDS, cancer patients undergoing chemotherapy, and transplant recipients, are more susceptible to severe disease.

When Should You See a Doctor for Shigellosis?

Seek medical care immediately for bloody diarrhea with high fever, signs of severe dehydration, severe abdominal pain, or symptoms in young children, elderly, or immunocompromised individuals. Emergency care is needed if you cannot keep fluids down, have no urination for 8+ hours, or experience confusion.

While mild cases of shigellosis may resolve on their own with supportive care, the infection can become serious and even life-threatening. Knowing when to seek medical attention is crucial for preventing complications and ensuring appropriate treatment.

The most important warning sign is bloody diarrhea combined with fever. This combination suggests an invasive bacterial infection that may require antibiotic treatment. Unlike viral gastroenteritis, which is typically self-limiting, bacterial dysentery can worsen without proper medical care and may lead to serious complications.

You should contact a healthcare provider promptly if you experience any of the following after recent travel or potential exposure:

• Diarrhea containing blood or mucus
• Fever above 38°C (100.4°F) accompanying diarrhea
• Diarrhea lasting more than 3 days without improvement
• Severe or worsening abdominal pain
• More than 6 loose stools in 24 hours
• Recent travel to areas with known shigellosis outbreaks or poor sanitation

Emergency situations

Certain situations require emergency medical care. Call your local emergency number or go to the nearest emergency department immediately if you or someone you are caring for experiences:

• Severe dehydration: Signs include no urination for 8 or more hours, dark-colored urine, rapid heartbeat, dizziness when standing, sunken eyes, or extreme thirst
• Inability to maintain hydration: If vomiting prevents keeping any fluids down
• Altered mental status: Confusion, extreme drowsiness, or difficulty staying awake
• Seizures: Particularly in children with high fever
• Signs of shock: Cold, clammy skin, rapid breathing, weak pulse

Special considerations for vulnerable groups

Certain populations require lower thresholds for seeking medical care due to their increased risk of complications:

Infants and young children: Any infant under 3 months with fever and diarrhea needs immediate medical evaluation. For older infants and toddlers, seek care at the first sign of bloody stool, high fever, or reduced fluid intake. Children can deteriorate quickly from dehydration.

Elderly individuals: Adults over 65 are at higher risk for severe disease and complications. Their thirst mechanism may be impaired, making them more susceptible to dehydration. Any elderly person with bloody diarrhea should be evaluated promptly.

Immunocompromised patients: People with weakened immune systems may have atypical presentations and are at risk for more severe and prolonged illness. Early medical evaluation is essential.

Pregnant women: While shigellosis does not typically harm the fetus directly, severe dehydration and high fever during pregnancy can have adverse effects. Pregnant women with suspected shigellosis should seek medical care promptly.

What Can You Do at Home to Manage Shigellosis?

Home management of shigellosis focuses on preventing dehydration through oral rehydration, resting, and preventing spread to others. Drink small, frequent amounts of clear fluids or oral rehydration solution. Practice strict hand hygiene, avoid preparing food for others, and monitor for warning signs requiring medical care.

For mild cases of shigellosis that do not require immediate medical attention, proper home care can significantly improve comfort and support recovery. The cornerstone of home management is maintaining hydration and preventing spread to household members.

Preventing and treating dehydration

Dehydration is the most significant risk during any diarrheal illness. The body loses not only water but also essential electrolytes (sodium, potassium, chloride) with each loose stool. Replacing both water and electrolytes is crucial for recovery.

Oral rehydration solution (ORS): The World Health Organization recommends oral rehydration solution as the gold standard for preventing and treating dehydration from diarrhea. ORS is available at pharmacies worldwide and contains the optimal balance of glucose and electrolytes to promote absorption. If commercial ORS is unavailable, you can make a temporary substitute by mixing 6 teaspoons of sugar and 1/2 teaspoon of salt in 1 liter of clean water.

Drinking strategy: Rather than drinking large amounts at once, which may trigger nausea or vomiting, take small, frequent sips throughout the day. Aim for at least 200-250ml of fluid after each loose bowel movement to replace losses. Adults should aim for a minimum of 2-3 liters of total fluid intake daily during illness.

Other suitable fluids: In addition to ORS, other appropriate fluids include water, clear broths, diluted fruit juices (avoid acidic juices if nausea is present), and weak tea. Avoid caffeine, alcohol, and very sugary drinks, as these can worsen dehydration.

Hand hygiene and preventing spread

Given shigellosis's extreme contagiousness, strict hygiene measures are essential to protect others:

• Wash hands thoroughly: Use soap and water for at least 20 seconds, especially after using the toilet, before eating, and before preparing food. Hand sanitizers are less effective against Shigella than proper handwashing.
• Do not prepare food for others: Avoid handling food that others will eat until you have been symptom-free for at least 48 hours, or as advised by your healthcare provider.
• Clean bathroom surfaces: Regularly disinfect toilet handles, faucets, and other bathroom surfaces. Use a bleach-based cleaner for best results.
• Avoid swimming pools: Do not swim in pools, water parks, or natural bodies of water until at least 2 weeks after diarrhea has stopped.
• Launder soiled items separately: Wash clothing and bedding contaminated with stool in hot water with detergent.

Dietary considerations

During the acute phase of illness, appetite is usually reduced. Do not force yourself to eat if you feel nauseated. As symptoms improve, gradually reintroduce bland, easily digestible foods:

• Plain rice, bread, or crackers
• Bananas (help replace potassium)
• Boiled potatoes without skin
• Plain cooked chicken or fish
• Clear soups and broths

Avoid dairy products, fatty foods, spicy foods, and high-fiber foods until symptoms have completely resolved, as these can aggravate diarrhea.

How Is Shigellosis Treated?

Shigellosis treatment focuses on fluid replacement to prevent dehydration. Antibiotics are recommended for severe cases, immunocompromised patients, and to reduce transmission in high-risk settings. Common antibiotics include azithromycin, ciprofloxacin, and ceftriaxone. Most people recover within 5-7 days with proper care.

The treatment approach for shigellosis depends on disease severity, the patient's risk factors, and the need to prevent transmission to others. For all cases, maintaining adequate hydration is the foundation of treatment. The role of antibiotics varies based on individual circumstances.

Fluid replacement therapy

Preventing and correcting dehydration is the most critical aspect of shigellosis treatment. For mild to moderate cases, oral rehydration is usually sufficient. The WHO-recommended oral rehydration solution provides optimal electrolyte and glucose balance to maximize fluid absorption even when intestinal function is impaired.

For severe dehydration or when patients cannot tolerate oral fluids due to vomiting, intravenous (IV) fluid therapy becomes necessary. This typically requires hospitalization and allows for rapid correction of fluid and electrolyte deficits. IV fluids like normal saline or Ringer's lactate are administered until the patient is stable enough to resume oral intake.

Antibiotic therapy

Not every case of shigellosis requires antibiotics. Mild infections in otherwise healthy adults often resolve without antimicrobial treatment. However, antibiotics are recommended in several situations:

• Severe disease: Patients with high fever, bloody diarrhea, or signs of invasive infection
• Immunocompromised patients: Those with weakened immune systems need antibiotics to prevent complications
• Very young or very old: Infants, young children, and elderly patients benefit from treatment
• To reduce transmission: Food handlers, healthcare workers, and childcare workers may be treated to shorten the period of infectivity
• Outbreaks: During institutional or community outbreaks, antibiotics help control spread

The choice of antibiotic is complicated by increasing antimicrobial resistance in Shigella species worldwide. Historically, ampicillin and trimethoprim-sulfamethoxazole were first-line treatments, but resistance has made these less reliable. Current preferred antibiotics include:

• Azithromycin: Often the first choice, especially for children, due to its once-daily dosing and generally favorable resistance profile
• Ciprofloxacin: Effective option for adults, though fluoroquinolone resistance is increasing in some regions
• Ceftriaxone: Given by injection, used for severe cases or when oral antibiotics cannot be tolerated

Your healthcare provider may request culture and sensitivity testing of your stool sample to identify which antibiotics will be effective against your specific infection.

Hospital treatment

Hospitalization is necessary for patients with severe dehydration, inability to maintain oral intake, signs of complications, or certain high-risk conditions. Hospital care may include:

• Intravenous fluid therapy for rapid rehydration
• Intravenous antibiotics if oral medications cannot be tolerated
• Close monitoring of vital signs and fluid balance
• Management of complications such as electrolyte abnormalities
• Supportive care for fever and pain

What Are the Complications of Shigellosis?

Shigellosis complications include severe dehydration, hemolytic uremic syndrome (HUS), reactive arthritis, seizures in children, toxic megacolon, and bacteremia. While most people recover fully, complications can be life-threatening, particularly in children, elderly, and immunocompromised individuals.

Although the majority of shigellosis cases resolve without lasting problems, serious complications can occur, particularly in vulnerable populations. Understanding these potential complications helps in recognizing warning signs and seeking timely medical care.

Severe dehydration

The most common serious complication of shigellosis is severe dehydration resulting from fluid loss through diarrhea. Dehydration can progress rapidly, especially in young children and elderly adults. Severe dehydration can lead to kidney failure, shock, and death if not promptly treated with fluid replacement.

Hemolytic uremic syndrome (HUS)

HUS is a potentially life-threatening condition that can develop following infection with Shigella dysenteriae type 1, which produces Shiga toxin. This toxin damages blood vessel walls, leading to a triad of problems: destruction of red blood cells (hemolytic anemia), low platelet count (thrombocytopenia), and acute kidney failure.

HUS typically develops 5-10 days after the onset of diarrhea and affects children more commonly than adults. Symptoms include decreased urine output, fatigue, pallor, and easy bruising. HUS requires hospitalization and may necessitate dialysis or blood transfusions. While most patients recover, some may have permanent kidney damage.

Reactive arthritis

Reactive arthritis, also known as Reiter's syndrome, can develop weeks after a Shigella infection, even after the intestinal symptoms have resolved. This immune-mediated condition causes joint inflammation, particularly affecting the knees, ankles, and feet. Some patients also develop eye inflammation (conjunctivitis or uveitis) and urinary tract symptoms.

Reactive arthritis affects approximately 2-3% of people who have had shigellosis. It is more common in individuals who carry the HLA-B27 gene. While the condition usually resolves over several months, some patients experience chronic or recurring symptoms.

Neurological complications

Seizures are a recognized complication of shigellosis, occurring primarily in children. Febrile seizures may result from high fever, while other seizures may be related to electrolyte imbalances or the effects of bacterial toxins on the nervous system. In rare cases, encephalopathy (brain dysfunction) can occur.

Other complications

• Toxic megacolon: Severe inflammation can cause the colon to dilate dangerously, a surgical emergency
• Intestinal perforation: Rarely, the damaged intestinal wall can develop a hole, allowing contents to leak into the abdominal cavity
• Bacteremia: Bacteria may enter the bloodstream, leading to sepsis, particularly in immunocompromised patients
• Rectal prolapse: Severe straining during defecation can cause the rectum to protrude through the anus, especially in malnourished children

How Can You Prevent Shigellosis?

Prevent shigellosis by practicing thorough handwashing with soap and water, drinking only safe water, eating properly cooked foods, avoiding raw foods when traveling, and maintaining good personal hygiene. The key principle is "boil it, cook it, peel it, or forget it" when traveling to high-risk areas.

Since no vaccine against shigellosis is currently available for routine use, prevention relies entirely on hygiene practices and safe food and water consumption. These measures are particularly important for travelers and anyone caring for infected individuals.

Hand hygiene

Thorough handwashing is the single most effective measure for preventing shigellosis transmission. Wash hands with soap and water for at least 20 seconds:

• After using the toilet or changing diapers
• Before eating or preparing food
• After contact with someone who has diarrhea
• After touching potentially contaminated surfaces

Hand sanitizers containing at least 60% alcohol can supplement handwashing but are not as effective as soap and water for removing Shigella bacteria. Alcohol-based sanitizers should not replace handwashing, especially after using the toilet.

Safe food and water practices

When traveling to areas with poor sanitation or during outbreaks:

• Water safety: Drink only bottled water with intact seals, boiled water, or water treated with appropriate disinfection methods. Avoid ice cubes unless made from safe water.
• Food safety: Eat only foods that are thoroughly cooked and served hot. Avoid raw vegetables, salads, and unpeeled fruits. Be cautious with buffets where food may have been sitting at room temperature.
• The travel rule: "Boil it, cook it, peel it, or forget it" is a simple guide for food safety while traveling.
• Street food caution: While local street food can be tempting, ensure it is cooked thoroughly and served immediately from a hot source.

Preventing household spread

If someone in your household has shigellosis:

• The infected person should not prepare food for others until symptom-free for at least 48 hours
• Assign a separate bathroom if possible, or thoroughly disinfect shared bathrooms after each use
• Wash the infected person's clothing and bedding separately in hot water
• Do not share towels, washcloths, or eating utensils
• Keep young children away from the infected person as much as possible
• Supervise and assist children with handwashing

Special settings

Childcare centers: Proper diaper-changing procedures, staff hand hygiene, and exclusion of ill children are essential. Children with diarrhea should not attend childcare until cleared by a healthcare provider.

Healthcare facilities: Standard precautions plus contact precautions should be implemented for patients with suspected or confirmed shigellosis. Staff hand hygiene compliance is critical.

Swimming pools: People with diarrhea should not swim for at least 2 weeks after symptoms resolve. Proper pool chlorination reduces but does not eliminate transmission risk.

Frequently Asked Questions