Etiology 

The causes of diarrhoea can be classified as follows: 

i)  Infectious causes 

Viral  : Rota virus, Norwalk and allied viruses, Enterovirus, Influenza virus, measles virus. 

Bacterial  : E.coli, Shigella, Salmonella, Staphylococcus, Campylobacter Jeguni, Yersinia  enterocolitice, Clostridium dificile, Aeromoneus hydrophilia, Vibrio parahemolyticus,  klebsella. 

Parasities  : Giardia Larnbila, Entarnoeba  histolytica, Canadida albicans, Trichuris, Trichuria, Strongyliods stercoralis. 

Fungi  : Canadida albicans, Histoplasma capsulatum 

ii)  Drugs  : Antibiotics 

iii)  Diet  : Food poisoning, Food allergy, Overeating, Starvation

iv)  Necrotising enterocolitis 

v)  Other causes  : Intussusception, Uremic syndrome, Congenital aganglionic .  mgacolon, Neonatal drug withdrawal syndrome. 

Predisposing Factors 

1. Diarrhoea is more frequent in children under  the age of 2 years with peak incidence between six  to nine months. 
2. More common  in summer months with maximum frequency in rainy season. 
3. Children from poor families and poor sanitary environment. Poorly nourished children and also more in artificially fed children than breast fed children. 
4. Teething does not predispose the child to diarrhoea but during tooth eruption child puts dirty finger  and soiled object in mouth which leads to diarrhoea. 

Thus  introducing infection in gastrointestinal tract