There were age and seasonal features of the spread of submanifest forms of rotaviral infection with the aim of the assessment of their importance in epidemiology. In 2011-2015 2608 residents of Rostov-on-Don at the age from of 2 weeks to 90 years were examined by ELISA methods for the isolation of group A rotaviruses. The widespread of asymptomatic rotaviral infection was established in the population. Rotavirus was detected in 63.3% of patients aged of 0-1 year, 24.7% -from 2 to 14 years, and 12.5% - 15-90 years. There was revealed an active circulation of rotaviruses in all seasons of the year. In June and July, the infestation of adults is not reduced, children from 1 year to 14 years - 17.5% seems to be higher than in periods of seasonal rises of the morbidity rate. The high level of asymptomatic infection in summer, may indicate to a decline in circulation of epidemic strains and the predominance of avirulent variants of rotavirus. The heterogeneity of the viral populations increases, which creates conditions for the formation of a large number of new reassortants and genetic variants of the pathogen. Thus, asymptomatic infections prevailing among the population both serve as a major reservoir of viral gene pool, the source of new variants of the virus and play a major role in the immune selection of epidemic strains. There was substantiated the assumption that the cause a winter-spring seasonality of infection is the advantage in the spread of virulent strains of rotavirus over avirulent ones, which is realized at low temperatures that increase pathogen survival. Early summer-autumn surges in the incidence rate in the South of Russia can cause a skid by millions of tourists of new genotypes of rotavirus to the territory with favorable social conditions for their active circulation.