Does gastroenteritis cause blood in stool?

Gastroenteritis inflames the stomach or intestines, usually during an infection. When the bowel lining is inflamed, stool may contain streaks or mixed blood, often with diarrhoea, cramps, urgency, fever, nausea, or vomiting. The appearance can vary, and dark or tar-like stool may signal bleeding higher in the digestive tract. Blood can also come from piles, a small tear, inflammatory bowel disease, or other conditions. Because the cause cannot be confirmed from appearance alone, do not dismiss new or repeated bleeding.

Contact a healthcare professional promptly for advice about blood in stool, particularly if it is new, recurrent, or accompanied by diarrhoea. Drink small amounts regularly if you can, and note the colour, amount, frequency, pain, fever, vomiting, recent travel, sick contacts, and medicines. Avoid preparing food for others while you have diarrhoea. Do not take anti-diarrhoeal medicine without professional advice when stool contains blood or you have a fever.

Seek urgent help for heavy or continuing bleeding, black tar-like stool, severe abdominal pain, repeated vomiting, faintness, confusion, marked weakness, or signs of dehydration such as very little urine. Children, older adults, pregnant people, and anyone with a weakened immune system may need earlier assessment.

Ask whether you need an examination or stool testing, how to replace fluids safely, and which medicines to avoid. Tell the clinician when the bleeding began and whether it is mixed with diarrhoea or accompanied by fever or pain.