Persistent Diarrhoea
On this page
Direct answer
When watery diarrhoea crosses 14 days it becomes persistent diarrhoea, and the question changes from hydration to nutrition — the commonest mechanism is damaged mucosa with secondary lactase deficiency after an acute episode, aggravated by cow's milk protein enteropathy, giardiasis or cryptosporidiosis. Management continues breastfeeding, re-introduces feeds in a staged WHO sequence starting with reduced-lactose diets (curd or yogurt mixed with cereals), adds zinc, vitamin A and multivitamins, and treats the identifiable cause. Weight is the monitoring tool: a child not gaining on one diet step moves to the next within days.
What you must remember
- Definition: an episode of diarrhoea, watery or bloody, lasting 14 days or more; it typically begins as ordinary acute gastroenteritis that never settles, and it is a malnutrition-disease cycle.
- Secondary lactose intolerance, the hallmark mechanism: acidic stools (pH below 5.5), perianal excoriation, bloating after milk feeds, and stool reducing substances positive.
- Infectious causes to hunt: Giardia (cysts on microscopy, responds to metronidazole), Cryptosporidium (acid-fast oocysts, notorious in HIV), Cyclospora; an HIV test belongs in the work-up of any non-responder.
- Non-infective causes by age: cow's milk protein allergy in young infants (blood-streaked stools in a well baby), coeliac disease after six months once wheat enters the diet (failure to thrive, pot belly, wasted buttocks).
- WHO dietary staging: continue breastfeeding; Diet 1 is reduced-lactose — curd or yogurt-based, mixed with cereals — six or more small energy-dense feeds a day; Diet 2, if weight is not regained in three days, removes milk protein entirely (chicken, egg or soy with rice); an elemental formula follows in hospital if that fails.
- Micronutrients are obligatory: zinc, vitamin A, folate and multivitamins with minerals for at least two weeks — mucosal recovery is a nutritional job.
- Red flags for admission: dehydration, marked weight loss or failure to gain across diets, severe malnutrition, blood with systemic illness, or a caregiver unable to manage the feeding plan.
- Do not stop milk on suspicion alone: most children tolerate reduced lactose, and blanket milk withdrawal in Indian households frequently worsens nutrition.
Working through the diet ladder
A nine-month-old, weaned early onto diluted cow's milk, has had eight weeks of swinging watery stools and slipped two centiles. Stool pH 5.2 with positive reducing substances; microscopy shows giardia cysts. Two tracks run together: metronidazole for the giardia, and the diet ladder — breastfeeding continues, milk is replaced with curd-rice or yogurt-cereal mixes six times a day, zinc and vitamin A given. At day three he has gained nothing and stools remain acidic, so Diet 2 begins — a milk-free chicken-rice or soy feed, still energy-dense, still six small meals. Weight now moves, the excoriation heals, and the ladder is climbed back down toward normal family food with milk re-introduced gradually. A 14-month-old with a big wheat appetite, chronic irritability and a wasted bottom would instead trigger coeliac testing — serology then duodenal biopsy — because no diet fixes gluten enteropathy except gluten withdrawal. Know the mechanism, stage the diet, treat the parasite, monitor the weight.
Where students slip
The reflex to reach for "stronger antibiotics" heads the list — most persistent diarrhoea is post-infectious and dietary, and metronidazole belongs to proven giardia or amoebae, not to frustration. The second is stopping all milk on day one, which the WHO ladder deliberately avoids: reduce lactose first, eliminate protein only on failure. Third, missing coeliac disease in the older infant with "resistant" diarrhoea, and missing HIV in the child with cryptosporidiosis. Finally, forgetting the endpoint: a diet is judged on the scale at 72 hours, and examiners phrase the question exactly that way — "what next after failure of the first diet in three days".
Frequently asked questions
What defines persistent diarrhoea?
An episode lasting 14 days or more, usually beginning as acute watery diarrhoea, carrying a high risk of malnutrition and death in young children.
How is secondary lactose intolerance confirmed?
Stool pH below 5.5 with positive reducing substances, bloating and perianal excoriation after milk feeds — the signature of brush-border lactase loss after mucosal injury.
What is the first dietary step in the WHO algorithm?
Continue breastfeeding and start a reduced-lactose, cereal-based diet such as curd or yogurt mixed with rice, energy-dense, in six or more small servings daily.
When is the diet changed to a milk-free one?
If the child fails to regain weight after about three days on the reduced-lactose diet, milk protein is withdrawn in favour of chicken, egg or soy-based feeds.
Which parasite is notorious in persistent diarrhoea with HIV?
Cryptosporidium, identified by acid-fast oocysts in stool, along with other opportunists; HIV testing is part of the non-responder work-up.
How is response to treatment monitored?
By daily weight and stool pattern — weight gain within three days confirms the current step; failure demands escalation and a search for coeliac disease, allergy or missed infection.