Shigellosis: What It Is, How You Get It, and How It's Treated

Sudden stomach cramps, an urgent trip to the bathroom, and diarrhea that looks a little too bloody for comfort. If this happened after eating from a roadside stall or drinking water you weren't quite sure about, shigellosis could be the reason. It's one of the more common bacterial infections behind acute diarrhea in India, and while most cases clear up on their own, some need medical attention fast.

This guide covers what shigellosis is, how you actually get it, the symptoms to watch for, the tests doctors use to confirm it, and how it's treated.

What Is Shigellosis?

Shigellosis is an intestinal infection caused by a group of bacteria called Shigella. It's also known by its older name, bacillary dysentery. Unlike a typical viral stomach bug that passes in a day or two, shigellosis is bacterial, and it tends to inflame the lining of the colon, which is why the diarrhea it causes is often bloody or mucoid rather than just watery.

Shigella infections are especially common in developing regions with variable water quality and sanitation, and India is no exception. Globally, Shigella species are estimated to cause well over a hundred million diarrheal episodes each year, with the highest burden falling on young children. Knowing what shigellosis is matters because it changes how you approach treatment. Some viral infections just need time and fluids, but shigellosis sometimes calls for antibiotics, and getting that decision right depends on catching it early.

How Do You Get Shigellosis?

Shigellosis spreads through what's called the fecal-oral route. In plain terms, that means the bacteria travel from the stool of an infected person into someone else's mouth, usually through contaminated hands, food, water, or surfaces.

What makes Shigella particularly easy to catch is that it takes a very small number of bacteria to make someone sick, often as few as ten to a hundred organisms. That's a much lower dose than many other foodborne bacteria need, which is part of why shigellosis spreads so quickly in households, schools, and crowded settings.

Common ways people pick it up include:

• Drinking water that hasn't been properly treated or boiled
• Eating food prepared by someone who didn't wash their hands after using the toilet
• Touching contaminated surfaces, such as changing tables or diaper pails, and then touching your mouth
• Close contact with someone who currently has shigellosis or had it in the past couple of weeks
• Swimming in ponds, lakes, or pools that aren't properly chlorinated

In India, monsoon season tends to see a spike in shigellosis and similar infections, largely because of water contamination during heavy rains. Street food and unfiltered water are also common sources. Some groups face higher risk than others, including young children, older adults, people with weakened immune systems, and international travelers visiting regions with limited sanitation infrastructure.

Shigellosis Symptoms

Symptoms usually show up one to three days after exposure, though in some cases they can appear in as little as twelve hours. Here's what to watch for.

Common symptoms:

• Diarrhea, which is often watery at first and can become bloody or mucoid
• Abdominal cramps and pain
• Fever
• Nausea and sometimes vomiting
• Tenesmus, an urgent and frequent need to pass stool, even when little comes out

For most people, symptoms last around five to seven days and resolve without any lasting issues. But certain signs mean you shouldn't wait it out.

See a doctor promptly if you notice:

• Blood or mucus in the stool
• High or persistent fever
• Signs of dehydration, such as reduced urination, dizziness, or a very dry mouth
• Symptoms in an infant, elderly person, or someone with a weakened immune system

Rare but serious complications can include dehydration severe enough to need hospitalization, seizures in young children (usually linked to high fever), reactive arthritis appearing weeks after the infection, and in the most severe cases, hemolytic uremic syndrome, a condition that affects the kidneys and red blood cells. Bloodstream infections are also possible, particularly in people with weakened immunity.

How Is Shigellosis Diagnosed? What Tests Are Required

A doctor will usually start with your symptom history and a physical exam, but confirming shigellosis requires lab testing. Here are the tests typically used.

Stool culture. This is the gold standard test. A sample of your stool is sent to a lab, where technicians try to grow and identify the Shigella bacteria. Beyond confirming the diagnosis, a culture also allows for antibiotic susceptibility testing, which tells the doctor which antibiotics will actually work against that particular strain. This matters more than it used to, because antibiotic-resistant Shigella strains are becoming more common worldwide.

Stool microscopy. This is a quicker, cheaper first step. A lab technician looks at the stool sample under a microscope for signs of inflammation, such as white blood cells (fecal leukocytes) and blood. It doesn't confirm Shigella specifically, but it supports the diagnosis and helps rule out other causes.

PCR or molecular stool panels. Many labs now offer faster, DNA-based tests that can detect Shigella genetic material within hours instead of the days a culture takes. These are convenient, but they don't provide antibiotic susceptibility information, so a culture is often still needed alongside them, especially for more severe cases.

Blood tests. A complete blood count (CBC) and electrolyte panel may be ordered to check for signs of dehydration, infection severity, or complications, particularly if the illness is more than mild.

If you've had these tests done and you're staring at a stool culture report or a CBC full of unfamiliar terms, a medical report reader can help translate the values into plain language while you wait to discuss the results with your doctor.

Shigellosis Treatment

Most cases of shigellosis are mild and self-limited, meaning they get better on their own within a week without needing antibiotics.

Hydration comes first. Since diarrhea causes fluid and electrolyte loss, drinking oral rehydration solution (ORS) or plenty of fluids is the most important part of treatment for almost everyone with shigellosis. In cases of severe dehydration, IV fluids in a hospital setting may be needed.

Avoid anti-diarrheal medication. Drugs like loperamide, which slow down bowel movements, are generally not recommended for shigellosis. They can trap the bacteria and toxins in the gut longer, which may worsen the illness rather than help it.

Antibiotics, when needed. Not everyone with shigellosis needs antibiotics, but they're generally recommended for people with severe symptoms, bloody diarrhea, or a confirmed positive stool culture, and for high-risk groups such as young children, older adults, people with HIV or other immune conditions, food handlers, and healthcare workers. Commonly prescribed antibiotics include ciprofloxacin, azithromycin, and ceftriaxone. Because antibiotic resistance in Shigella is a growing concern globally, doctors increasingly rely on culture and susceptibility results to choose the right drug rather than guessing.

If a full course of antibiotics is prescribed, it's important to complete it even if symptoms improve early, to reduce the chance of the infection lingering or spreading to others.

How to Prevent Shigellosis

A few consistent habits go a long way in avoiding shigellosis altogether.

• Wash your hands with soap and water, especially after using the toilet, changing a diaper, and before eating or preparing food
• Stick to boiled, filtered, or properly treated drinking water, particularly during monsoon season or while traveling
• Be cautious with street food and raw foods that may have been prepared or washed with contaminated water
• Avoid swallowing water while swimming in ponds, lakes, or pools that aren't chlorinated
• Keep anyone with active symptoms away from food preparation, childcare, or healthcare duties until they've fully recovered

There is currently no vaccine for shigellosis, so prevention comes down almost entirely to hygiene and safe food and water practices.

Getting Started

Shigellosis is common, usually manageable, and rarely something to panic over, but it's not something to ignore either, especially if there's blood in the stool or the person affected is a young child or elderly. Knowing the symptoms, getting the right test done, and understanding when antibiotics are actually necessary can make the difference between a rough week and a hospital visit.

If you've recently had a stool test or blood work done and want a simple explanation of what the results mean, you can upload your report for a free plain-language analysis on Bharat Swasth's website or send it over on WhatsApp.

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Disclaimer: This content is for educational purposes only and is not a substitute for professional medical advice. Always consult a qualified doctor for diagnosis or treatment decisions.