Seroprevalence of anti-H5 antibody in rural Cambodia, 2007

Since 2005, eight patients with H5N1 infection were laboratory confirmed in Cambodia. Despite the widespread of highly pathogenic avian influenza H5N1 virus and the intense exposure to poultry, there is growing evidence that H5N1 viruses may not be easily transmitted to human.

To evaluate the frequency of H5N1 transmission in rural Cambodia, to identify potential risk factors for H5N1 in humans and to explore the extent of asymptomatic and clinically mild illness among humans.

A seroepidemiologic survey was conducted, 9 weeks after the recognition that H5N1 infection caused the death of a 13 years old female in April 2007. Blood specimens were collected from 700 participants for H5N1 serological testing. All participants were interviewed with standardized questionnaire to collect information about poultry exposure.

Eighteen (2.6%) of the 700 villagers were tested positive cases for H5N1 antibodies. These 18 individuals were more likely than seronegative participants to report bathing or swimming in the community pond (p=0.04).

The seroprevalence of H5N1 antibodies was higher than previously reported in the other investigations conducted in Cambodia and Thailand. This finding reinforces the overwhelming evidence that the virus continues to circulate widely in settings where human have high exposure to poultry. Our results, provides additional evidence suggesting that bathing or swimming in the community ponds, remains important potential risk factor for H5N1 infection. Both wild birds and domestic poultry have free access to these ponds which are also used for aquaculture through the dumping of poultry feces for fish feeding.