Shigella or stomach bug? Doctor explain the warning signs you shouldn't ignore

A stomach upset is something most people experience at some point. It is often blamed on eating outside food, drinking contaminated water, consuming spicy meals or catching a seasonal infection.

In many cases, symptoms improve within a day or two with rest, fluids and simple home care. However, health experts warn that not all cases of diarrhoea are the same.

When symptoms include blood or mucus in stools, fever, severe abdominal pain and a constant urge to use the toilet, the condition may be more serious than a routine stomach infection.

These symptoms could point to dysentery, an inflammatory infection of the intestine. One of the most important causes of dysentery is Shigella, a highly contagious bacterium that can spread quickly through contaminated food, water and poor hand hygiene.

According to Dr Bhavini Shah, Head of Clinical Microbiology at Neuberg Diagnostics, understanding the difference between common diarrhoea and dysentery is important because the treatment, risks and public health implications can be very different.

DIARRHOEA AND DYSENTERY ARE NOT THE SAME

Many people use the terms diarrhoea and dysentery interchangeably, but they refer to different conditions.

Diarrhoea usually involves passing loose, watery stools, often in large quantities. It generally affects the small intestine and is commonly caused by viral infections, contaminated food, food poisoning, parasites or digestive disorders.

Common causes of diarrhoea include viruses such as rotavirus and norovirus. Certain bacteria, including Vibrio cholerae and some strains of Escherichia coli (E. coli), can also cause watery diarrhoea. Parasites such as Giardia and Cryptosporidium may also be responsible.

In most uncomplicated cases, the main concern is dehydration. Treatment usually focuses on drinking enough fluids, using oral rehydration solutions and, in children, zinc supplementation.

WHAT MAKES DYSENTERY DIFFERENT?

Dysentery is an inflammatory infection that usually affects the large intestine or colon. Unlike ordinary diarrhoea, it often causes frequent passage of small amounts of stool mixed with blood or mucus.

Patients may also experience:

• Fever
• Severe abdominal cramps
• Pain during bowel movements
• A constant urge to pass stool even when the bowel is nearly empty

This persistent urge is known as tenesmus and is considered a key symptom of dysentery.

Because dysentery involves inflammation and damage to the intestinal lining, it can be more serious than routine diarrhoea and may require medical evaluation.

WHY SHIGELLA IS A CAUSE OF CONCERN

Shigella is one of the most common bacterial causes of dysentery. The bacteria invade the lining of the colon, triggering inflammation and causing symptoms such as bloody stools, mucus, fever and painful cramps.

Unlike a typical stomach upset that may improve with hydration alone, Shigella infections can sometimes require specific treatment. The infection spreads easily through contaminated hands, food and water, making outbreaks possible in schools, hostels, day-care centres and crowded households.

Doctors say that because Shigella is highly contagious, identifying cases early is important not only for the patient but also for preventing further spread in the community.

WHY TESTING MATTERS

One of the biggest challenges is that Shigella symptoms can resemble those caused by several other infections.

Conditions that may produce similar symptoms include:

• Enteroinvasive E. coli (EIEC)
• Campylobacter infection
• Non-typhoidal Salmonella infection
• Enterohaemorrhagic E. coli (EHEC)
• Clostridioides difficile infection
• Amoebic dysentery caused by Entamoeba histolytica

Because different organisms require different treatment approaches, guessing the cause based on symptoms alone can be risky.

Dr Shah says stool testing plays a crucial role in identifying the exact organism responsible for the illness. Laboratory testing helps doctors determine whether the infection is caused by Shigella or another pathogen and guides appropriate treatment decisions.

THE GROWING CONCERN OF ANTIBIOTIC RESISTANCE

Experts also stress the importance of testing because of increasing antimicrobial resistance.

Overuse and misuse of antibiotics have made some Shigella strains more difficult to treat. As a result, doctors increasingly rely on diagnostic testing before deciding which antibiotics, if any, should be prescribed.

Accurate diagnosis can help avoid unnecessary antibiotic use while ensuring that patients who need treatment receive the most effective medication.

WHEN SHOULD YOU SEE A DOCTOR?

Medical attention should be sought if diarrhoea is accompanied by:

• Blood or mucus in stools
• High fever
• Severe abdominal pain
• Signs of dehydration
• Persistent vomiting
• Frequent bowel movements with little stool output

These symptoms may indicate dysentery or another serious intestinal infection that requires medical evaluation.

A simple stomach upset and Shigella infection may appear similar at first, but there are important differences. Large-volume watery stools without blood are more likely to indicate common diarrhoea. Blood or mucus in stools, fever, abdominal cramps and frequent urgent bowel movements are warning signs of dysentery.

Since Shigella falls into this category and can spread rapidly, early diagnosis, proper testing and timely treatment are essential to protect both individual patients and the wider community.