Stomach bug and blood in stool: what to know

Blood in stool during a stomach bug needs medical attention because infection is one possibility, but bleeding can have other causes. Bright-red blood may come from the lower bowel or rectum, while dark, sticky stool can indicate bleeding higher in the digestive tract. The amount, colour, frequency, pain and your general condition all matter.

Gastroenteritis can inflame the bowel and cause diarrhoea, cramps, vomiting or fever. A small streak of bright blood can also follow frequent loose stools or irritation around the anus. Blood mixed through stool, repeated bleeding, severe cramps or bloody diarrhoea should not be attributed to a stomach bug without an assessment. Inflammatory bowel conditions such as Crohn's disease or ulcerative colitis, diverticular disease, polyps and bowel or rectal cancer are other possible explanations; these conditions can present with blood in stool, but the symptom alone does not identify the cause.

Contact a clinician promptly and describe the stool colour, whether blood is on the paper or mixed in, how often it has happened, and whether vomiting or diarrhoea continues. Sip oral fluids regularly and avoid alcohol while you are unwell. Keep track of medicines, including products containing iron or medicines that affect bleeding, and mention recent travel, suspicious food or sick contacts. Do not use leftover antibiotics or anti-diarrhoeal medicine unless a clinician advises it, particularly when stool contains blood.

Seek urgent medical care for heavy or ongoing bleeding, black tarry stool, faintness, confusion, marked weakness, severe abdominal pain, repeated vomiting, or signs of dehydration such as very little urine and a dry mouth. Go urgently as well if a child, older adult, pregnant person or someone with a serious long-term illness is affected. Blood with diarrhoea and fever warrants same-day advice. A clinician may consider stool testing, blood tests or an examination to identify the source.

Could the pattern and colour of bleeding fit an infection, or do I need tests for another bowel condition? Which fluids and medicines are suitable for me? What changes should prompt emergency care? If bleeding settles, when should I arrange follow-up?