epidemiological characteristics include the non-explosive , diffuse character of morbidity , the absence of definite regularity in the occurrence of the disease among different age groups , increased morbidity among medical personnel an public service workers , the seasonal character of the infection ( winter and spring ) , the absence of any influence of the factors commonly contributing to the mass spread of enteric diseases on the morbidity level , as well as the negative results of numerous bacteriological ( virological ) investigations made with the aim of isolating the known causative agents of enteric infections .
C0009450
infection
C0012634
diseases