Int. J. Environ. Res. Public Health 2012, 9 899 EU921357–EU921362 and EU921396–EU921399 for NoV, HQ268775–HQ268790 for AdV, HQ268791–HQ268793 for HAstV, HQ662310–HQ662328 for EV and HQ425480–HQ425483 for AiV. 2.4. Environmental Investigation The hygienic conditions of the areas affected by gastroenteritis outbreaks and water supply and sewage pipelines were inspected by the health officials of Mumbai. A drinking water sample of 5 liters was collected on 17th March, 2006 from each of the two sources utilized by the consumers. Water samples were concentrated from 5 liters to ~200 mL by membrane based ultrafiltration using a membrane with an exclusion limit of 60,000 Daltons [32] and subsequently a volume of 200 mL was concentrated to ~2 mL in an Amicon cell (Millipore) and stored in aliquots at −70 °C till tested for enteric viruses (RVA, RVB, NoV, AdV, HAstV, EV and AiV). 3. Results 3.1. Epidemiological Investigation Two outbreaks of acute gastroenteritis were reported in the months of March and October 2006, respectively, from two and one localities of southern Mumbai. The outbreak affected localities, each 1–1.5 km2 in area that was occupied by 4500 and 7000 inhabitants respectively. Nearly 7% and 4% of the inhabitants were affected by the disease, respectively, during the months of March and October, 2006. In order to establish the incidence of gastroenteritis outbreaks, the number of gastroenteritis cases admitted monthly to GTH and JJH was recorded for the year, 2006. Figure 1 shows that the frequencies of admission for gastroenteritis in the hospitals were increased remarkably in GTH and JJH in March and October, 2006 respectively. The records of both hospitals also showed higher number of admissions in 2006 [886 (GTH), 1322 (JJH)] as compared to those in 2005 [278 (GTH), 477 (JJH)]. Figure 1. Frequencies of admission of patients with gastroenteritis referred to GTH and JJH in the year 2006. * includes 66 children, 12 adolescents and 222 adults hospitalized during 13th–26th March, 2006; ** includes 53 children, 13 adolescents and 198 adults hospitalized during 5th–15th October, 2006.