The underlying cause is an infectious agent in almost all casesof persistent diarrhea whereas in chronic diarrhea it is not infectious.
Persistent Diarrhea is usually of abrupt onset. On the other hand, the onset is very insidious in chronic diarrhea.
In such children reduce milk (but don’t omit completely) for 7 days. If the diarrhea worsens during this period, switch over to a lactose free diet (omit milk only but milk products and all other foods are allowed) for at least two more weeks. It takes approximately 3 weeks for the villi to regenerate and resume effective absorptive function after transient villus damage in diarrhea.
If there is no improvement refer to pediatric gastroenterologist.
Some children with persistent diarrhea may be in an immuno-suppressed state as in HIV infection.