Shigellosis: Causes, Symptoms, Diagnosis, and Prevention

The Shigella genus consists of four major species: Shigella dysenteriae, Shigella flexneri, Shigella boydii, and Shigella sonnei. Each of these species is associated with varying degrees of illness severity, with Shigella dysenteriae being the most severe due to its production of the Shiga toxin. Shigella sonnei is the most common cause of infection in industrialized nations, while Shigella flexneri is more prevalent in developing regions. These bacteria invade the cells lining the intestines, leading to inflammation, ulcers, and severe diarrhea that may contain blood or mucus. Because Shigella is highly resistant to stomach acid, only a small number of bacteria—sometimes fewer than 100—are needed to cause an infection.

The primary mode of transmission for Shigella is the fecal-oral route. This means that infection occurs when an individual ingests even a tiny amount of contaminated fecal matter. Poor hand hygiene, inadequate sanitation, and the consumption of contaminated food or water are key contributors to outbreaks. In many cases, young children are particularly vulnerable because they frequently put their hands in their mouths and may not practice proper hygiene. Additionally, certain groups, such as travelers to regions with poor sanitation, people in institutional settings, and those with weakened immune systems, face an increased risk of infection. Infected individuals can continue to spread the bacteria for weeks, even after symptoms have subsided, making control efforts challenging.