One of the most contentious debates among epidemiologists has been over whether there are a lot of undiagnosed `mild’ or asymptomatic human H5N1 (bird flu) cases in South East Asia.
The argument goes that if there are a large number of undetected mild cases, and we are only seeing the `tip of the iceberg’ or most serious of human infections, our concerns over the 60% CFR (Case Fatality Ratio) may be overstated.
Today we have three new journal articles and a commentary appearing in the Journal of Infectious Diseases on the H5N1 virus.
One of these studies details a seroprevalence study conducted on more than 600 members of a Cambodian village where 2 human H5N1 cases were detected in 2006.
Maggie Fox of Reuters picks up the story.
By Maggie Fox, Health and Science Editor
WASHINGTON (Reuters) - The H5N1 bird flu virus can infect people without causing noticeable symptoms, but only rarely, according to a report published on Thursday.
A survey of more than 600 people in Cambodian villages where two children died from the virus shows seven more were apparently infected, but without having known about it.
The study, published in the Journal of Infectious Diseases, also suggests that people may become infected by swimming in ponds where infected birds have dabbled.
"Although these results cannot be considered to be representative without broader confirmation, they show that, in some settings, surveillance may substantially miss H5N1 virus infections," Dr. Sylvie Briand and and Dr. Keiji Fukuda of the World Health Organization wrote in a commentary.
"Seven (1 percent) of 674 villagers tested seropositive for influenza H5N1 antibodies and did not report severe illness," they wrote. This means their bodies had at some point fought off an H5N1 infection.
Most were male, 18 or younger, and were more likely than other villagers to have reported bathing or swimming in household ponds. They all lived in wooden houses on stilts with well or pond water as the only water source for the family and none had known contact with the two children who died.
For those expecting a large number of asymptomatic infections, this study will be disappointing. Only 1% of the villagers tested showed that they had contracted, and fought off, the H5N1 virus.
How typical this village’s experience is, compared to others, is something we will need more research in order to determine.
All 4 articles are freely available from the Journal of Infectious Diseases.
1717 Avian Influenza A (H5N1) Virus and 2 Fundamental Questions
Sylvie Briand and Keiji Fukuda
1726 Risk Factors for Human Illness with Avian Influenza A (H5N1) Virus Infection in China
Lei Zhou, Qiaohong Liao, Libo Dong, Yang Huai, Tian Bai, Nijuan Xiang, Yuelong Shu, Wei Liu, Shiwen Wang, Pengzhe Qin, Min Wang, Xuesen Xing, Jun Lv, Ray Y. Chen, Zijian Feng, Weizhong Yang, Timothy M. Uyeki, and Hongjie Yu
1735 Ecologic Risk Factor Investigation of Clusters of Avian Influenza A (H5N1) Virus Infection in Thailand
Thanawat Tiensin, Syed Sayeem Uddin Ahmed, Suvichai Rojanasthien, Thaweesak Songserm, Parntep Ratanakorn, Kridsada Chaichoun, Wantanee Kalpravidh, Surapong Wongkasemjit, Tuangthong Patchimasiri, Karoon Chanachai, Weerapong Thanapongtham, Suwit Chotinan, Arjan Stegeman, and Mirjam Nielen
1744 Risk Factors Associated with Subclinical Human Infection with Avian Influenza A (H5N1) Virus—Cambodia, 2006
Sirenda Vong, Sowath Ly, Maria D. Van Kerkhove, Jenna Achenbach, Davun Holl, Philippe Buchy, San Sorn, Heng Seng, Timothy M. Uyeki, Touch Sok, and Jacqueline M. Katz