Risk factors associated with subclinical human infection with avian influenza A (H5N1) virus--Cambodia, 2006.
BACKGROUND
We conducted investigations in 2 villages in Cambodia where outbreaks of influenza H5N1 occurred among humans and poultry to determine the frequency of and risk factors for H5N1 virus transmission.


METHODS
During May 2006, approximately 7 weeks after outbreaks of influenza H5N1 among poultry occurred, villagers living near households of 2 patients with influenza H5N1 were interviewed about potential H5N1 exposures and had blood samples obtained for H5N1 serological testing by microneutralization assay. A seropositive result was defined as an influenza H5N1 neutralizing antibody titer of 1:80, with confirmation by Western blot assay. A case-control study was conducted to identify risk factors for influenza H5N1 virus infection. Control subjects, who had seronegative results of tests, were matched with H5N1-seropositive persons by village residence, households with an influenza H5N1-infected poultry flock, sex, and age.


RESULTS
Seven (1.0%) of 674 villagers tested seropositive for influenza H5N1 antibodies and did not report severe illness; 6 (85.7%) were male. The 7 H5N1-seropositive persons, all of whom were aged<or=18 years, were younger than participants who tested seronegative for H5N1 antibodies (median age, 12.0 years vs. 27.4 years; P=.03) and were more likely than were the 24 control subjects to report bathing or swimming in household ponds (71.4% vs. 20.8%; matched odds ratio, 11.3; P=.03).


CONCLUSIONS
Avian-to-human transmission of influenza H5N1 virus remains low, despite extensive poultry contact. Exposure to a potentially contaminated environment was a risk factor for human infection.
Vong
Sirenda
S
Institut Pasteur in Cambodia, Phnom Penh, Cambodia. svong@pasteur-kh.org
Ly
Sowath
S
Van Kerkhove
Maria D
MD
Achenbach
Jenna
J
Holl
Davun
D
Buchy
Philippe
P
Sorn
San
S
Seng
Heng
H
Uyeki
Timothy M
TM
Sok
Touch
T
Katz
Jacqueline M
JM
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D002160:Cambodia / Q000453:epidemiology; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D004781:Environmental Exposure; D006801:Humans; D007223:Infant; D053124:Influenza A Virus, H5N1 Subtype; D007251:Influenza, Human / Q000453:epidemiology* / Q000821:virology*; D008875:Middle Aged; D011200:Poultry; D012189:Retrospective Studies; D012307:Risk Factors; D016036:Seroepidemiologic Studies; D013997:Time Factors; D055815:Young Adult
D000914:Antibodies, Viral