The bacterium Shigella is a highly contagious pathogen that targets the human intestinal tract, causing the infectious disease known as shigellosis. As a common bacterial cause of diarrheal illness worldwide, understanding how this infection spreads is crucial. The ease with which it moves between people and environments contributes to its persistent circulation, especially in settings with poor sanitation.
Understanding Shigellosis
Shigellosis is the disease caused by infection with one of the four main species of Shigella bacteria. Following exposure, the typical incubation period is short, ranging from one to four days, though symptoms usually start within 48 hours. The infection primarily affects the large intestine, causing a sudden onset of symptoms.
The primary symptom of shigellosis is severe diarrhea, often accompanied by blood, mucus, or pus in the stool (bacillary dysentery). Other symptoms include fever, painful stomach cramps, and tenesmus, which is the painful urge to pass stool. While anyone can contract the illness, young children under five, older adults, and immunocompromised individuals face a higher risk of severe disease. These groups are more vulnerable to complications like dehydration and electrolyte loss.
Routes of Transmission
Shigella is highly infectious due to its very low infectious dose; ingesting as few as 10 to 100 bacterial organisms can cause disease. This efficiency makes the primary transmission mechanism, the fecal-oral route, particularly effective. The bacteria are shed in the stool of infected people, and transmission occurs when these microscopic particles are transferred to the mouth of another person.
Direct person-to-person contact is a major pathway for spread, especially within households and childcare centers. This happens when an infected person does not thoroughly wash their hands after using the bathroom or changing a diaper and then touches surfaces or other people. The organism is hardy and can survive on contaminated surfaces, toys, or clothing long enough to be passed on.
A second route involves the ingestion of contaminated food. Food becomes tainted when handled by an infected person with poor hand hygiene during preparation or serving. Produce may also be contaminated if grown or washed with water containing human sewage. Ready-to-eat foods that are not cooked after handling pose a high risk.
The third common pathway is through contaminated water sources, particularly recreational water like lakes or inadequately chlorinated swimming pools. Swallowing even a small amount of this water while swimming can lead to infection. Untreated drinking water or ice made from unsafe water is also a vehicle for transmission, especially in areas with poor sanitation. Shigellosis can also be transmitted through sexual activities involving contact with feces.
Strategies for Prevention
Breaking the cycle of fecal-oral transmission relies on consistent hygiene practices. Thorough handwashing with soap and running water is the most effective preventative measure against the spread of Shigella. Hands must be washed for at least 20 seconds, especially after using the toilet, changing diapers, assisting someone with diarrhea, and before preparing or eating food.
Strict adherence to safe food handling practices is another defense. This involves preventing cross-contamination between raw and cooked foods and ensuring all produce is rinsed under clean, potable water. Foods should be cooked to the correct internal temperatures to kill bacterial contaminants.
When traveling to regions with questionable sanitation or water quality, individuals should exercise caution regarding what they consume. It is best to only drink sealed, bottled water or water that has been properly treated, such as by boiling or chemical disinfection. Avoiding ice, fountain drinks, and unpeeled raw fruits and vegetables further reduces the risk of exposure.
In childcare and healthcare facilities, isolating individuals with active diarrhea is necessary to prevent wider outbreaks. Caregivers must employ barrier precautions, such as wearing gloves when handling soiled linens or changing diapers, followed immediately by handwashing. These combined measures limit the movement of the bacteria from the environment to the mouth.
Management and Recovery
For most individuals, shigellosis is a self-limiting infection that resolves within five to seven days. The primary focus of care is supportive, aiming to prevent and manage dehydration by replacing lost fluids and electrolytes, ideally with an oral rehydration solution.
Anti-motility medications, such as loperamide, are not recommended because they can prolong the illness or worsen the condition by keeping the bacteria in the digestive tract longer. Antibiotic therapy is usually reserved for severe cases, high-risk individuals, or to reduce transmission risk in group settings. If prescribed, completing the entire course of antibiotics is important, even if symptoms improve quickly.