Molecular epidemiology of rotaviruses in Bulgaria: annual shift of the predominant genotype.

Rotavirus molecular epidemiology investigations provide important information about the incidence of rotavirus diseases and rotavirus strains in circulation in the prevaccine era. The purpose of this investigation was to study the burden of rotavirus disease, rotavirus strain diversity, and epidemiology specificities of rotavirus infections in Bulgaria. A total of 3,130 stools collected between 2005 and 2008 were tested by immune enzyme tests. G-P genotype identification of rotavirus strains were performed by reverse transcriptase polymerase chain reaction (RT-PCR). Rotavirus etiology was confirmed in 32.4% of the samples tested. Rotaviruses affected predominantly children under 5 years of age (95.5%), with a peak prevalence between the ages of 7 and 36 months. Four of the five globally distributed rotavirus strains (G1P[8], G2P[4], G4P[8], and G9P[8]) constituted 97.7% of all rotavirus strains in circulation. However, annual shifts of predominant rotavirus G-P genotypes were observed from season to season-G4P[8] was predominant in rotavirus season 2004/2005 (56.8%), but was replaced by G9P[8] in 2005/2006 (77.7%), and G2P[4] (41.6%) and G1P[8] (39.5%) in the following two consecutive rotavirus seasons. Year-round circulation of rotaviruses in the country with increased incidence in the winter-spring season and unexpected peaks preceding the rotavirus seasons were observed. Molecular epidemiology data are needed in Bulgaria for health policy makers in order to introduce routine rotavirus vaccination. The monitoring of rotavirus genetic diversity in Bulgaria in the postvaccination period will contribute to a successful rotavirus vaccination program.