Stomach flu and blood in diarrhoea: what to know

Gastroenteritis can irritate the digestive tract and cause diarrhoea, nausea, abdominal pain or fever. Visible blood, red streaks, or black, tar-like stool needs a clinician to consider other causes as well, including more significant inflammation or bleeding. The colour, amount, frequency, and whether you also have vomiting or fever help guide the assessment.

Diarrhoea and vomiting can remove fluid and salts quickly. Signs of dehydration include a dry mouth, marked thirst, dizziness, unusual sleepiness, or passing much less urine. Young children, older adults, and people with long-term health conditions can become unwell sooner.

Contact a healthcare professional promptly and describe when the bleeding began, what it looked like, how often you have diarrhoea, and whether you can keep fluids down. Until you receive advice, take frequent small sips of water or an oral rehydration drink, if suitable for you. Rest, wash your hands after using the toilet, and avoid preparing food for other people while unwell.

Do not take an anti-diarrhoeal medicine to suppress bloody diarrhoea unless a clinician specifically recommends it. Keep a note of your medicines, recent travel, unusual foods, and anyone else who is ill; these details can help identify the likely source.

Seek urgent medical care if bleeding is heavy or increasing, stool is black and sticky, you have severe or worsening abdominal pain, fainting, confusion, repeated vomiting, or signs of dehydration. A high fever or feeling suddenly very unwell also warrants prompt assessment. Children and frail adults should be assessed early when blood appears.

Ask whether you need stool testing, which fluids are appropriate, and which warning signs should send you to urgent care. Mention pregnancy, recent antibiotics, immune problems, and any blood-thinning medicine.