This study is designed to estimate the changes in the etiology and epidemiology of acute gastroenteritis in children aged less than 18 years after the implementation of rotavirus vaccine in the Estonian national immunization program in July 2014.

The two-year study period started in February 2015.

The study population consists of all children less than 18-years-old hospitalized due to acute gastroenteritis (AGE) to seven Estonian hospitals participating in this study. Expected sample size is about 2000 patients.

Hospitals that participate in this study are Tartu University Hospital, West-Tallinn Central Hospital, Tallinn's Children Hospital, Pärnu Central Hospital, South-Estonian Hospital, Kuressaare Hospital and Ida-Viru Central Hospital.

Before enrollment all patients are asked to give an informed consent. After enrollment the study doctor completes electronic questionnaire regarding the patients demographic data, medical history and vaccinations. Specific database for our study has been created by company Vision 5D. After completing electronic questionnaire the doctor collects 2 stool samples each 2 ml of volume into Eppendorf tubes produced by our study laboratory. The samples are transported to our study laboratory where they are tested for rotavirus, norovirus G1, G2, astrovirus, adenovirus and sapovirus with Fast-Track Diagnostics real-time assay kit FTD Viral Gastroenteritis. The samples positive for rotavirus are refrigerated at -70 degrees for further genotyping and sequencing.

Inclusion Criteria:

• children aged < 18 year
• hospitalized due to acute gastroenteritis

Exclusion Criteria:

• children aged > 18 years
• gastroenteritis due to known non-infectious causes

All children less than 18-years-old hospitalized due to acute gastroenteritis to seven Estonian hospitals participating in this study from 02.2015-09.2016