Table 2. Antibody titers to influenza A/Anhui/1/2013(H7N9) in an anonymized population serosurvey, Lower Mainland, British Columbia, Canada, May 2013*.

Age group, y	No. patients†	Median age, y	% Female	Mean GMT (95% CI)‡	No. (%, 95% CI)§
					With titer >10	With titer >20
<10	49	4	47	5	0	0
10–19	48	16	67	5	0	0
20–29	49	27	69	5	0	0
30–39	50	34	90	5	0	0
40–49	50	46	60	5	0	0
50–59	49	55	49	5	0	0
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)¶
70–79	50	75	42	5	0	0
80–89	50	83	40	5.4 (5–5.9)	4 (8.0, 0.5–15.5)	1 (2.0, 0–5.9)¶
>90	51	92	73	5.3 (4.9–5.6)	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).