Prevalence of Antibodies against Avian Influenza A (H5N1) Virus among Cullers and Poultry Workers in Ho Chi Minh City, 2005

BACKGROUND: Between 2003 and 2005, highly pathogenic avian influenza A (H5N1) viruses caused large scale outbreaks in poultry in the Ho Chi Minh City area in Vietnam. We studied the prevalence of antibodies against H5N1 in poultry workers and cullers who were active in the program in Ho Chi Minh City in 2004 and 2005. METHODOLOGY/PRINCIPAL FINDINGS: Single sera from 500 poultry workers and poultry cullers exposed to infected birds were tested for antibodies to avian influenza H5N1, using microneutralization assays and hemagglutination inhibition assay with horse blood. All sera tested negative using microneutralization tests. Three samples showed a 1∶80 titer in the hemagglutination inhibition assay. CONCLUSIONS/SIGNIFICANCE: This study provides additional support for the low transmissibility of clade 1 H5N1 to humans, but limited transmission to highly exposed persons cannot be excluded given the presence of low antibody titers in some individuals.