Some animal workers in southern China, home of the first H10N8 avian flu infections, may have had asymptomatic or subclinical infections with the strain even before the first human case was recognized in November 2013, so surveillance should continue in this population as well as in healthcare workers, say the authors of a study today in BMC Medicine.

The researchers, from Guangzhou, China, and Durham, N.C., retrospectively studied archived serum samples from 720 animal workers and 107 non–animal workers from May through August 2013 during a surveillance program for novel zoonotic flu in occupationally exposed individuals.

Samples were tested by hemagglutination inhibition (HI) assay; those with positive reactivity to H10N8 (defined as titer > 1:20) were further tested by microneutralization (MN) assay. Questionnaires given by the animal workers regarding risk factors for H10N8 were also evaluated.

Of the 827 samples, 21 (2.5%) tested positive, three with titers of 1:40. None of those who tested positive had flu symptoms during the 3 months before sampling was done. Of the three people with the higher titers, two had MN antibody titers of 1:40, evidence of possible previous H10N8 infection, and one had a titer of 1:80, indicative of a probable previous infection. All three were animal workers.

H10N8 virus was first identified in a duck in Guangdong province during 2012; the authors say the virus infected dogs in the area as well. They point out that the Guangdong province has been a hotbed of novel influenza virus generation, including the H7N9 strain that is the source of an ongoing outbreak that began in 2013 and has caused more than 450 cases.
Oct 27 BMC Med abstract