Diarrhea is one of the most common reasons for people to seek medical advice - but it can range from being a mild, temporary condition, to be life threading condition. It is estimated that there are 2 billion cases of diarrheal disease every year globally, and that 1.9 million children below the age of 5 years, mostly in developing countries, die annually.

Secretory diarrhea has many causes as infection with bacteria, viruses or protozoa. It results from increased chloride secretion, decreased sodium absorption, or increased mucosal permeability . Parasitic pathogens induce Secretory diarrhea as they infect and damage the absorptive villus tips, leaving Secretory crypts unbalanced, to cause net secretion and diarrhea. Parasitic causes include Cryptosporidium parvum or hominis ,Capillaria philippinensis and Giardia lamblia. Cryptosporidiosis is also recognized as a cause of prolonged and persistent diarrhea in children and persons with impaired immunity. The disease is transmitted via the fecal-oral route from infected hosts. It can be also transmitted following animal contact, ingestion of water (mainly during swimming), or through food. Cryptosporidium has emerged as the most frequently recognized cause of water-associated outbreaks of gastroenteritis. This is because of the oocyst stage in its life cycle; Cryptosporidium can resist disinfection, including chlorination, and can survive for a prolonged period in the environment.

Inclusion Criteria:

1. Children presented with secretory diarrhea(acute watery diarrhea) attend to out clinic lab of Assiut University pediatric hospital or admitted in pediatric hospital(gastroenterology department) during the study period.
2. adult patients having acute watery diarrhea attend to out clinic labs of Assiut University hospital or admitted in gastroenterology, nephrology and oncology department of hospital during the study period.

Exclusion Criteria:

1. viral and bacterial causes of diarrhea
2. Patients who were already diagnosed as intestinal inflammatory disease as irritable bowel syndrome.
3. Autoimmune conditions, such as ulcerative colitis, Crohn's disease and coeliac disease.

-Children presented with secretory diarrhea(acute watery diarrhea) attend to out clinic lab of Assiut University pediatric hospital or admitted in pediatric hospital(gastroenterology department) during the study period.

2-adult patients having acute watery diarrhea attend to out clinic labs of Assiut University hospital or admitted in gastroenterology, nephrology and oncology department of hospital during the study period.