Detection by microneutralization of antibodies against avian influenza virus in an endemic avian influenza region

Detection by microneutralization of low-titre antibodies (anti-H5 micro-NT titre ≤1 : 80) against avian influenza virus (H5N1) is usually taken to be a false-positive result. In this prospective study of 242 intensive-care unit patients admitted for severe community-acquired pneumonia, the prevalence of low-titre anti-H5 micro-NT was 2.4%. Prior exposure to poultry was the sole independent risk factor for these low-titre antibodies (adjusted OR 42.41; 95% CI 22.45-64.51; p <0.001). We suggest that low anti-H5 micro-NT titres be interpreted in conjunction with plausible poultry, environmental and human exposure to H5N1.