MSU Extension

Shigella is a bacteria that infects the small intestine of human beings, apes, and monkeys and is commonly passed through contaminated food and water. There are four species of the bacteria and, as a group, they are one of the most communicable and severe forms of bacteria-induced diarrhea. Shigella is closely related to E. coli, and in some scientific circles, the deadly E. coli O157:H7 is actually thought to be better categorized as Shigella.

Worldwide, there are about 165 million cases of shigellosis, the disease caused by infection by Shigella, and over 98 percent occur in third-world countries. In the U.S, the Centers for Disease Control and Prevention (CDC) estimate that 300,000 - 400,000 cases occur each year, leading to 600-1000 deaths yearly. Most cases occur in summer months, between July and October.

How do you catch it? 

Shigella bacteria are transmitted via the fecal-oral route, which means infected fecal matter is ingested through the mouth. Most infections are transmitted person-to-person, but can also be spread through contaminated food, water, and sometimes through sexual contact with an infected person. On average, it takes as little as 100 bacterial cells to infect a person. Depending on the person’s health, as few as 10 cells can cause infection.

According to the CDC, Shigella is the third most common foodborne pathogen in the U.S., and about one-third of all shigellosis cases are thought to have been transmitted by contaminated food or water. The most common food sources are sandwiches and salads that may have been touched by dirty hands during preparation. It is also sometimes referred to as the “picnic bacteria” because Shigella can easily be transmitted by flies that have landed in and around outdoor restrooms and then land on food at picnics and outdoor events. Raw vegetables contaminated in the field with infected water are also a common source. Swimming in and swallowing contaminated water is another way to contract this bacteria.

Symptoms and Duration:

• Are mostly gastrointestinal and include diarrhea, stomach cramps, and fever.
• Usually occur 1-3 days after ingestion and last about 5-7 days, though bacteria can still be transmitted for up to two weeks after symptoms have subsided. 

Who is most at risk?

While the disease can infect anyone, the demographic most affected by Shigella (in the U.S.) is children under the age of 4. It is often passed through childcare centers and schools because it is so highly contagious, and easily passed via shared toys and poor hand hygiene in these settings. Other more-susceptible groups are travelers to foreign countries (because of the increased prevalence of the disease, especially in underdeveloped countries), and persons who are HIV positive (studies show that HIV positive persons have prolonged infections and a higher incidence of the infection getting into the bloodstream, causing sepsis).

How to prevent it

• Proper and frequent hand washing is the easiest way to prevent transmission of this bacteria, especially after using the bathroom, changing a diaper, or cleaning up after/caring for someone who is sick. Supervise handwashing practices of small children after using the bathroom is also important.
• Wash fruits and vegetables before serving/cooking and never prepare food while sick.
• At outdoor events with food, cover foods to prevent flies from landing on it.
• Avoid swallowing water from lakes, ponds, and pools. 
• When travelling in underdeveloped countries only drink bottled or boiled water, avoid ice cubes, and eat only thoroughly cooked, hot foods.

If you or someone in your family is suffering from a diarrheal disease, it is best to stay home to prevent spread to others. The rule of thumb is to stay out of the public for at least 24 hours after your last symptom. In most cases, Shigella will subside on its own after a few days. Treatment with antibiotics can shorten the duration of illness but antibiotic-resistant strains are becoming more common.

For more information regarding Shigella check out the resources listed below. Check back next month to learn more about the Big 6 Pathogens from MSU Extension.

Further resources:

• Centers for Disease Control
• Foodsafety.gov
• “It Was Probably Something You Ate: A Practical Guide to Avoiding and Surviving Food-borne Illness” by Nicholas Fox

Other articles in this series

• Introduction
• E. coli
• Salmonella
• Viruses