Fig. 5

Seroprevalence of antibodies to avian influenza A (H5N1) virus estimated through random effects models by type of exposure and virus clade, using three antibody titer thresholds (World Health Organization recommended, modified World Health Organization recommended, and non-standardized antibody titer thresholds to define a seropositive result). World Health Organization (WHO) recommendations refer to a neutralizing (NT) antibody titer ≥ 1:80 with a positive result using a 2nd assay method, i.e., hemagglutination inhibition test (HAI) (HAI antibody titer ≥ 1:160), enzyme-linked immunosorbent assay, or western blot assay. The modified WHO definition of a seropositive result refers to an NT antibody titer ≥ 1:80 with a positive result using a 2nd confirmatory assay (i.e., HAI antibody titer ≥ 1:40, ELISA, or western blot assay). The non-standardized seropositive definition refers to criteria used to define a seropositive result other than the WHO or modified WHO definitions. Data are presented if A(H5N1) virus-specific antibodies were detected. a A(H5N1) virus antibody seroprevalence by type of exposure. b Changes in A(H5N1) virus antibody seroprevalence by type of exposure after excluding studies related to A(H5N1) outbreaks in Hong Kong in 1997. c A(H5N1) virus antibody seroprevalence by virus clade