Int. J. Environ. Res. Public Health 2012, 9 910 2 week period each from March and October, 2006 was revealed during the examination of record of all of the months of 2006 and the previous year from both hospitals (Figure 1). The number of cases declined during next two months and remained at usual frequency of admission for gastroenteritis. The records also underscored the presence of disease in patients of all age groups in both outbreaks. Interestingly, both outbreaks that occurred in different seasons showed predominance of RVA and EV infections. However, frequencies of the occurrence of these viruses and also of other enteric viruses were not different in two incidents (Table 1, p > 0.05). Commonly circulating RVA genotypes have been found to be associated with the outbreaks of gastroenteritis that occurred worldwide [38-40]. In the present study, RVA strains of G1P[8] and G2P[4] specificity that have been described earlier in sporadic infections in Mumbai were detected only in October, while the strains from the March outbreak remained nontypeable [16]. The other enteric viruses displayed similar genotypic specificities in the two outbreaks. The higher prevalence of NoV GII over GI in acute gastroenteritis cases has been reported from India and other parts of the World [15,41]. The NoV genotypes detected in the Mumbai outbreaks also belonged to GII (GII.4, GII.7, GII.12 and GII.3/GII.13). This finding was similar to that reported earlier for the sporadic infections from Western India [15]. It is of note that GII.2 identified only in Mumbai was not detected in any other city from Western India, while GII.b infections were detected in cities other than Mumbai [15]. In view of this observation, a separate molecular epidemiological study is required to know the diversity of NoVs circulating in Mumbai. In the present study, EV-76, EV-84, EV-89, EV-90, CA-13, CA-17, CA-19, CA-19/22, CA-21, Echo-21 and Echo-32 types were identified for the first time in Western India. However, Echo-11 identified in the gastroenteritis outbreak from Southern India [35] was not detected. The high prevalence and genetic diversity of EV strains noted in the present study are indicative of the association of EVs with acute gastroenteritis and suggest the need for surveillance of EV infections in India. AiVs have been described to be present in the mixed infections together with other enteric pathogens [40]. Interestingly, in this study, all four patients excreting AiV showed absence of other enteric viruses. RVA, AdV, calicivirus, HAstV and other viruses have been described to be excreted continually in patients with immunodeficiency syndrome [42]. However, such a syndrome was not recorded in an infant who showed presence of infection with RVA, RVB, NoV and Adv in this study. The present study identified single and mixed enteric viral infections during the outbreaks of gastroenteritis and suggested that the affected individuals were highly exposed to multiple enteric viruses. The study documented for the first time the circulation of RVB, AdV, HAstV and AiV in Mumbai. Most of the enteric viruses examined in the study were detected in both summer (March) and winter (October) months. These findings indicate the necessity of monitoring of sporadic cases of gastroenteritis in Mumbai city for single and mixed enteric viral infections. Viruses causing acute gastroenteritis are known to be excreted in large quantities in human faeces and find their way out in the sewage system. Thus, sewage water is a good source of a variety of enteric viruses circulating in any region/community [40]. An accidental mixing of the sewage water with the drinking water supply provides an opportunity to multiple enteric viruses to infect humans simultaneously and cause disease outbreaks. In the present study, water samples tested negative for enteric viruses. However, contamination of drinking water was reflected by brown color and malodor