2.1 Study site
The Indian Council of Medical Research (ICMR)-National Institute of Virology (ICMR-NIV) in Pune, Maharashtra state is a part of the Indian Rotavirus Surveillance Network supported by the Indian Council of Medical Research (ICMR), New Delhi since 2005.  The National Rotavirus Surveillance Network (NRSN) is a multi-centric project conducted at four referral and seven regional centers across India. Each center has peripheral in-patient facilities that collect the clinical data and specimens and send them to the corresponding referral and regional laboratories for testing and characterization. The criteria for recruitment, stool sample collection, laboratory detection, and genotype characterization protocols used were common at all sites. ICMR-NIV, Pune is one of the referral centers that represents the West Zone of India. The stool specimens collected from the West Zone consisting of four cities and seven hospitals, namely Pune (KEM Hospital, Bharati Hospital and Shaishav Clinic), Mumbai (Lokmanya Tilak Municipal GH & Medical College), Ahmadabad (BJ Medical College & Civil Hospital), and Surat (Surat Municipal Institution of Medical Education & Research) during 2013–2016 were included in the present study. These hospitals are tertiary-level health care centers, providing both general and specialized medical care.
2.2 Enrolment criteria and clinical assessment
A case of acute gastroenteritis was defined as the passage of ≥3 watery stools in a day with or without associated symptoms such as vomiting, fever, and abdominal pain.  All patients were examined for fever, number of episodes and duration of vomiting and diarrhea, extent of dehydration and treatment for the assessment of disease severity score (Ruuska and Vesikari, 1990). According to the scores obtained, the disease condition of   each patient was categorized as mild (scores 0–5), moderate (scores 6–10), severe (scores 11–15) and very severe (scores 16–20).