Detection of type A and B influenza viruses in clinical materials by immunoelectronmicroscopy

Direct immunoelectronmicroscopy (IEM) was used for detecting influenza subtype A(H1N1), A(H3N2) and type B viruses in nasopharyngeal washings or swabs collected during three consecutive periods of enhanced influenza incidence. Virus identification was performed with immune rat sera and in the case of the A(H3N2) subtype also with convalescent human sera. In all the materials examined influenza virus was demonstrated by isolation in chick embryos or by immunofluorescence in infected tissue cultures. IEM detected subtype A(H1N1), A(H3N2) and type B viruses in 6 of 13, all 5 and 3 of 8 washings, respectively. Immune complexes were observed in only those materials from which virus was isolated already in the first chick embryo passage, which was evidence that a positive IEM result depended on the amount of virus present in the material. The use of immune sera against two antigenically distinct A(H1N1) strains, A/Khabarovsk/77 and A/England 403/80, did not considerably influence the IEM result.