The HI test modified by ether treatment in the sero-epidemiological surveillance of influenza B

Ether-treated influenza B haemagglutination inhibition (HI) antigen was used in a study of serum collections from three different epidemic seasons. For diagnostic purposes, ether treatment increased the efficacy of the HI test by about 50% over the conventional HI technique, raising it to the same level of sensitivity as the complement fixation (CF) test. The treatment reduced the specificity of the HI test, but its reliability in the diagnosis of influenza B infections was only slightly diminished. With regard to evaluation of the immune status of a given population, an HI test using ether-treated antigen from the epidemic influenza B strain seems to give more relevant information about the antibody level associated with protection than a conventional HI test using untreated virus antigen.