I should have picked up this CIDRAP report by Lisa Schnirring when it came out yesterday: Tests show high H7N9 antibodies in Chinese poultry workers. Excerpt:
Adding to the evidence that poultry are the source of China's H7N9 influenza outbreak, a serology study in the southern Guangdong province city of Shenzhen found evidence of asymptomatic or mild infections in poultry workers, with levels increasing in the outbreak's second wave.
Researchers, however, found no evidence of infection when they looked at blood samples from the general population. The team from Shenzhen and the University of Hong Kong published their findings yesterday in an early online edition of Clinical Infectious Diseases.
Blood sampling compared spring and fall waves
They collected blood samples from retail and wholesale poultry workers in May 2013 from all 10 of the city's districts and again in late December 2013 in seven districts where environmental swabs had tested positive for the virus. The team obtained samples from 501 workers in May and from 375 in December. In December the virus was identified in market environmental samples, and the first human case in Shenzhen detected.
For the general public, the authors collected blood samples in March and September of 2013 with the goal of recruiting 70 people in each of four age-groups. For both groups they tested for antibodies to both H7N9 and H5N1 using hemagglutination-inhibition (HI) assays.
The researchers found a hemagglutination-inhibition antibody titer of at least 1:160 in 7.2% of poultry workers in May and in 14.9% in December, a rise that was consistent with the second wave of H7N9 activity in China, with Guangdong as one of the hot spots. None of the participants had confirmed H7N9 infections, and investigators didn't find evidence of infection in any of the general public group for either testing period.
The team pointed out that other studies of H7N9 seroprevalence in Chinese poultry workers showed much lower levels. For example, a study based on sampling in Zhejiang province in April and May of 2013 found 1.3% had antibody titers suggesting earlier infection.
Looking for risk factors, the researchers found that being female and having occupational exposure for 10 or more years was associated with infection. The team said the increased risk in women may reflect their having the major share of poultry duties for that region, which include selling poultry, defeathering, and cleaning. They said the longer work history could be related to reduced preventive measures or may reflect greater susceptibility to infection in older people.