This study also documents the early incidence of rotavirus disease in India. The percentage of children with dehydrating gastroenteritis who were less than six months of age was as high as 12%. The youngest case recorded was one month old at the time of

hospitalization. RGFP966 An earlier study from central India showed that rotavirus disease was more common during cooler months, with seasonal peaks matching the lowest temperatures [7]. In this study, a distinct winter peak was seen in the months of December to February during the total 16 months of surveillance across 12 sites in India, especially in northern India which has a distinct winter season from November to February. Interestingly, the sites

in southern India did not demonstrate this trend as the area experiences the least annual variation in temperature of the four regions. The worldwide emergence of the G12 strain in 2005 and its increasing incidence during the past two years parallels the emergence and subsequent spread of G9 strains that occurred approximately a decade ago. In the mid-1990s, G9P[6] NU7441 and G9P[8] strains were reported in India, Japan, the United Kingdom, and the United States. Subsequently, G9P[8] spread globally, and it currently accounts for 4.1% of all rotavirus infections [8]. In our study, a higher percentage of G12 (17.74%) was observed especially in the Eastern part of India as compared to the rest of India. Various studies have found G12 strains in association with multiple VP4 Carnitine dehydrogenase types, namely P[4], P[6], P[8], and P[9], suggesting re-assortment among commonly circulating strains [9] and [10]. The increased reporting of infection with G12 strains may be associated with re-assortment, resulting

in generation of a strain that is better adapted to replication in humans, similar to the events that preceded the spread of G9 strains in the past decade. The emergence of G12 strains highlights the need for a surveillance system to respond rapidly to changes in circulating virus and to ensure that vaccines remain effective against emerging strains. Reported G12 cases from our study provided further evidence of the notion that G12 strains should no longer be considered as unusual or rare strains but that they exhibit a capacity to spread among children just like human rotavirus strains of other commonly seen G types. In addition to the challenges posed by the emergence of new strains in the population under surveillance, we found high levels of circulation of unusual recombinant strains, such as G1P[4], G1P[6], G2P[6], G2P[8], G9P[4], and G9P[6] in different parts of the country. This indicates that there may be both regional and temporal variations in rotavirus strain predominance, which will be important to consider when assessing the impact of vaccination on rotavirus strains.