When to worry about blood in stool with gastroenteritis

Infection can irritate or injure the bowel lining, producing diarrhoea with streaks of red blood or mucus. Cramping, nausea, vomiting, fever, and urgency may occur alongside it. Blood is not a reason to assume the infection is harmless or to diagnose its cause at home: some infections need specific testing and treatment, and bleeding can have other explanations. Black, tar-like stool is a different warning pattern and needs urgent assessment.

Contact a healthcare professional promptly about bloody diarrhoea, particularly after travel, unsafe food or water, recent antibiotics, or contact with someone who was ill. Sip oral rehydration fluid if you can keep it down. Wash hands carefully and avoid preparing food for others while unwell. Do not take anti-diarrhoeal medicine when there is blood or fever unless a clinician specifically advises it.

Go urgently for inability to keep fluids down, very little urine, a dry mouth with worsening weakness, faintness, confusion, severe or localised abdominal pain, a swollen abdomen, persistent vomiting, heavy or continuing bleeding, black stool, or a high fever with marked illness. Children, older adults, pregnant people, and people with reduced immunity can become dehydrated quickly and should be assessed early.

Do I need stool testing or treatment for a particular infection? How can I replace fluids safely? Which medicines should I avoid? What signs of dehydration should my household watch for, and when should I return if the bleeding continues?