Volume 22, Number 1—January 2016
Avian Influenza A(H7N9) Virus Infection in 2 Travelers Returning from China to Canada, January 20151
|Age group, y||No. patients†||Median age, y||% Female||Mean GMT (95% CI)‡||No. (%, 95% CI)§
|With titer >10||With titer >20|
|60–69||50||65.5||56||5.3 (4.9–5.7)||3 (6.0, 0.0–12.6)||1 (2.0, 0–5.9)¶|
|80–89||50||83||40||5.4 (5–5.9)||4 (8.0, 0.5–15.5)||1 (2.0, 0–5.9)¶|
||3 (5.9, 0.0–12.4)
||1 (2.0, 0–5.8)¶
|All||496||50||59||5.1 (5–5.2)||10 (0.9, 0.2–1.7)#||3 (0.3, −0.1 to 0.7)#|
*Titers were measured by hemagglutination inhibition assay by using horse erythrocytes as previously described (6); assays were conducted at the National Microbiology Laboratory, Canada’s influenza reference laboratory in July 2013. GMT, geometric mean titer.
†Serum samples were collected in May 2013; 5 samples had insufficient serum and were excluded from the analyses (8).
‡Titers were assessed in duplicate. Titers <10 were assigned a value of 5. GMT of duplicate titers derived as individual titers and group GMTs derived by age and overall.
§No patients had a titer >40.
¶Further assessed by microneutralization (MN) assay, according to procedures described by the Centers for Disease Control and Prevention (Atlanta, GA, USA); available by request. MN titers for all 3 samples were <10.
#Age-standardized (direct method) to the 2013 Fraser Valley and Greater Vancouver, British Columbia, Canada, population projections (BC Stats, 2013: http://www.bcstats.gov.bc.ca/StatisticsBySubject/Demography/PopulationProjections.aspx).
- Lam TT, Zhou B, Wang J, Chai Y, Shen Y, Chen X, Dissemination, divergence and establishment of H7N9 influenza viruses in China. Nature. 2015;522:102–5 .
- European Centre for Disease Prevention and Control. Human infection with avian influenza A(H7N9) virus. Fourth update, February 2, 2015 [cited 2015 Jul 23]. http://ecdc.europa.eu/en/publications/Publications/RRA-Influenza-A-H7N9-update-four.pdf
- To KKW, Chan JFW, Chen H, Li L, Yuen K-Y. The emergence of influenza A H7N9 in human beings 16 years after influenza A H5N1: a tale of two cities. Lancet Infect Dis. 2013;13:809–21.
- Skowronski DM, Li Y, Tweed SA, Tam TWS, Petric M, David ST, Protective measures and human antibody response during an avian influenza H7N3 outbreak in poultry in British Columbia, Canada. CMAJ. 2007;176:47–53.
- European Centre for Disease Prevention and Control. Risk assessment guidelines for infectious diseases transmitted on aircraft (RAGIDA)—influenza. 2014 [cited 2015 Sep 6]. http://ecdc.europa.eu/en/publications/Publications/influenza-RAGIDA-2014.pdf
- Centers for Disease Control and Prevention. Modified hemagglutination-inhibition (HI) assay using horse RBCS for serologic detection of antibodies to H7 subtype avian influenza virus in human sera. Version 1 [cited 2015 July 23]. https://consise.tghn.org/site_media/media/articles/160713_Modified_Hemagglutination_Inhibition_Assay_Using_Horse_RBCs.pdf.
- Skowronski DM, Janjua NZ, De Serres G, Purych D, Gilca V, Scheifele DW, Cross-reactive and vaccine-induced antibody to an emerging swine-origin variant of influenza A virus subtype H3N2 (H3N2)v. J Infect Dis. 2012;206:1852–61.
- Skowronski DM, Chambers C, Sabaiduc S, Janjua NZ, Li G, Petric M, Pre- and postpandemic estimates of 2009 pandemic influenza A(H1N1) seroprotection to inform surveillance-based incidence by age, during the 2013–2014 epidemic in Canada. J Infect Dis. 2015;211:109–14.
- Gao H-N, Lu H-Z, Cao B, Du B, Shang H, Gan J-H, Clinical findings in 111 cases of influenza A (H7N9) virus infection. N Engl J Med. 2013;368:2277–85.
- Zhang A, Huang Y, Tian D, Lau EH, Wan Y, Liu X, Kinetics of serological responses in influenza A(H7N9)-infected patients correlate with clinical outcome in China, 2013. Euro Surveill. 2013;18:20657 .
- Yang S, Chen Y, Cui D, Yao H, Lou J, Huo Z, Avian-origin influenza A(H7N9) infection in influenza A(H7N9)–affected areas of China: a serological study. J Infect Dis. 2014;209:265–9.
- Guo L, Zhang X, Yu X, Chen L, Zhou H, Gao X, Human antibody responses to avian influenza A(H7N9) virus, 2013. Emerg Infect Dis. 2014;20:192–200.
- Chen Z, Liu H, Lu J, Luo L, Li K, Liu Y, Asymptomatic, mild, and severe influenza A(H7N9) virus infection in humans, Guangzhou, China. Emerg Infect Dis. 2014;20:1535–40.
- Ip DK, Liao Q, Wu P, Gao Z, Cao B, Feng L, Detection of mild to moderate influenza A/H7N9 infection by China's national sentinel surveillance system for influenza-like illness: case series. BMJ. 2013;346:f3693.
- Pabbaraju K, Tellier R, Wong S, Li Y, Bastien N, Tang JW. Full-genome analysis of avian influenza A(H5N1) virus from a human, North America, 2013. Emerg Infect Dis. 2014;20:887–91 .
1Preliminary results from the population serosurvey were presented at the CACMID-AMMI Canada 2014 Annual Conference, April 3–5, 2014, Victoria, British Columbia, Canada.