Human rotaviruses are characterized by which of the following statements?

Rotaviruses were initially identified by direct electron microscopy (EM) of duodenal mucosa of infants with gastroenteritis. Subsequent studies in several countries have shown them to be the cause of 30 to 40% of acute diarrhea in infants. They are non-lipid-containing RNA viruses with a double-shelled capsid. Although the virus has been serially propagated in human fetal intestinal organ cultures, cytopathic changes are minimal or absent; multiplication is detected by immunofluorescence. Numerous methods for rotavirus antigen detection, including radioimmunoassay, counter immunoelectrophoretic is, and enzyme-linked immunosorbent assay, have been developed and found to be about as effective as EM.