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Shigellosis (Shigella Infection) – A Practical Patient Guide

Overview

Shigellosis is an acute intestinal infection caused by bacteria of the genus Shigella. The disease is characterized by diarrhea—often bloody—and abdominal cramps. It spreads primarily through the fecal‑oral route, meaning that ingestion of contaminated food, water, or hands can transmit the organism.

Who it affects: While anyone can become infected, the highest rates occur in children under five, travelers to endemic areas, men who have sex with men (MSM), and people living in crowded or unsanitary environments such as refugee camps or day‑care centers.

Prevalence: According to the World Health Organization (WHO), shigellosis accounts for an estimated 80–165 million cases worldwide each year, resulting in up to 600,000 deaths, most of them in low‑income countries. In the United States, the CDC reports roughly 500,000 infections annually, with the majority being caused by Shigella sonnei and S. flexneri.<sup>1</sup>

Symptoms

Symptoms typically appear 1–3 days after exposure (incubation period) and may last from a few days up to a week. The severity can range from mild to severe, especially in young children, the elderly, and immunocompromised individuals.

• Diarrhea – watery to bloody stools; may contain mucus or pus.
• Abdominal cramps – often severe and worsen after meals.
• Fever – low‑grade (≤38.5 °C) to high (≥39 °C) in some cases.
• Urgent need to defecate (tenesmus) – a feeling of incomplete evacuation.
• Nausea & vomiting – more common in children.
• Loss of appetite and weight loss due to decreased oral intake.
• Dehydration signs – dry mouth, reduced urine output, dizziness, or sunken eyes.
• Blood in stool – may appear as bright red blood or “currant‑jelly” stools, especially in severe cases.
• General malaise – fatigue, headache, and muscle aches.

In infants, symptoms may include irritability, fever, and a sudden increase in the frequency of stools. Some people become asymptomatic carriers, shedding bacteria for weeks after recovery, which can perpetuate outbreaks.

Causes and Risk Factors

What causes shigellosis?

Shigellosis is caused by four main species of Shigella:

• Shigella sonnei – most common in industrialized nations.
• Shigella flexneri – prevalent in low‑ and middle‑income countries.
• Shigella dysenteriae – associated with severe dysentery and high mortality.
• Shigella boydii – less common, geographically limited.

The bacteria invade the lining of the large intestine, causing inflammation and cell death, which leads to the classic bloody diarrhea.

Risk Factors

• Age: Children <5 years old have the highest incidence.
• Travel: Visiting areas with poor sanitation (e.g., parts of Africa, South Asia, Central America).
• Close‑contact settings: Day‑care centers, prisons, nursing homes.
• Sexual practices: Oral‑anal contact increases risk, especially among MSM.
• Immunocompromise: HIV, cancer chemotherapy, organ transplantation.
• Antibiotic resistance: Prior use of antibiotics can select for resistant Shigella strains, making infections harder to treat.

Diagnosis

Early clinical suspicion is essential, especially during outbreaks or in high‑risk groups. Diagnosis is confirmed with laboratory testing.

Stool Tests

• Culture – gold standard; stool is plated on selective media (e.g., MacConkey, XLD) to grow Shigella. Takes 24–48 hours.
• Polymerase chain reaction (PCR) – rapid (often <12 hours) and highly sensitive; can identify species and resistance genes.
• Rapid antigen tests – less widely used but provide point‑of‑care results.

Additional Tests (if needed)

• Complete blood count (CBC) – may show leukocytosis.
• Electrolytes & renal function – assess dehydration severity.
• Blood cultures – reserved for severe cases with systemic signs.

Because symptoms overlap with other bacterial or viral gastroenteritis, a stool test is the only way to differentiate shigellosis from, for example, Salmonella, Campylobacter, or norovirus infection.

Treatment Options

Most healthy adults recover without antibiotics within 5–7 days. However, treatment goals are to reduce symptom duration, prevent complications, and limit transmission.

Rehydration – First‑line

• Oral rehydration solution (ORS) – the cornerstone for mild‑to‑moderate dehydration. WHO‑recommended formula contains sodium, potassium, glucose, and citrate.
• Intravenous fluids – required for severe dehydration, hypotension, or when the patient cannot tolerate oral intake.

Antibiotic Therapy

Antibiotics are indicated for:

• Severe illness (high fever, >6 watery stools per day, or bloody stools).
• Infants, the elderly, or immunocompromised patients.
• Persistent diarrhea lasting >4 days.
• Prevention of spread during outbreaks.

Choice of drug is based on local resistance patterns (CDC reports rising resistance to ampicillin and trimethoprim‑sulfamethoxazole). Common regimens include:

• Ciprofloxacin 500 mg PO BID for 3 days (first‑line in many regions).
• Azithromycin 500 mg PO once daily for 3 days – useful where fluoroquinolone resistance is high.
• Ceftriaxone 2 g IV daily – reserved for severe cases or when oral therapy is impossible.

Always complete the full prescribed course, even if symptoms improve, to prevent resistance.

Adjunctive Therapies

• Anti‑motility agents (e.g., loperamide) – generally avoided because they may prolong bacterial shedding; may be used under medical supervision in selected adult patients without high fever or blood in stool.
• Probiotics – some evidence suggests they shorten diarrhea duration, though they are not a substitute for rehydration or antibiotics.

Living with Shigellosis

Even after symptoms resolve, careful self‑care helps prevent relapse and spread.

• Stay hydrated – continue oral fluids and ORS until stool returns to normal consistency.
• Diet – eat bland, low‑fat foods (BRAT diet: bananas, rice, applesauce, toast) and gradually reintroduce fiber.
• Hygiene – wash hands with soap and water for at least 20 seconds after using the bathroom, before handling food, and after changing diapers.
• Isolation – avoid work, school, or daycare for at least 24 hours after the last bloody stool or while fever persists.
• Cleaning – disinfect bathroom surfaces with a bleach solution (1 part 5% bleach to 9 parts water) daily during the infectious period.
• Follow‑up – see a clinician if diarrhea lasts beyond a week, if you experience weight loss, or if you develop new symptoms.

Prevention

Because shigellosis spreads easily, public‑health measures and personal habits are crucial.

Individual Practices

• Wash hands thoroughly with soap and running water, especially after using the toilet, changing diapers, and before eating.
• Avoid consuming raw or undercooked foods and unpasteurized milk when traveling to high‑risk regions.
• Drink only bottled, boiled, or treated water abroad; use water purification tablets if necessary.
• Practice safe sexual behaviors – use barrier protection during oral‑anal contact.
• Disinfect surfaces regularly in households with a recent case.

Community/Public‑Health Strategies

• Ensure safe drinking water and proper sewage disposal.
• Implement strict hygiene protocols in day‑care centers and schools (hand‑washing stations, routine cleaning).
• Rapid outbreak investigation and reporting to local health departments.
• Education campaigns targeting high‑risk groups (MSM, travelers, caregivers).
• Vaccines are under development; none are currently licensed, but clinical trials are ongoing (e.g., Shigella conjugate vaccines).

Complications

When untreated or severe, shigellosis can lead to serious health problems:

• Severe dehydration – electrolyte imbalances can cause kidney injury or seizures.
• Hemolytic‑uremic syndrome (HUS) – a rare but life‑threatening condition characterized by kidney failure, anemia, and low platelets, most often linked to S. dysenteriae toxin production.
• Septicemia – bacterial entry into the bloodstream, especially in immunocompromised patients.
• Reactive arthritis – joint inflammation occurring weeks after infection.
• Persistent carrier state – some individuals continue to shed bacteria for months, posing a public‑health risk.

When to Seek Emergency Care

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Sources: CDC – Shigellosis, Mayo Clinic, WHO Fact Sheet, CDC Antibiotic Guidance, NIH Journal Review, 2020.

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