. Author manuscript; available in PMC: 2018 Mar 16.

Published in final edited form as: J Infect Dis. 2018 Mar 13;217(7):1078–1088. doi: 10.1093/infdis/jiy013

Table 2.

Timing of First Blood Specimen Collection and Hemagglutinin Inhibition (HAI) and Neutralizing Antibody (Ab) Titers Among Critically Ill Adolescents and Adults Hospitalized With 2009 Pandemic Influenza A(H1N1) Virus Infection—Canada, 2009–2011

Characteristic	Patients, No.	Time From Symptom Onset to Baseline Blood Specimen Collection, d		Baseline Acute-Phase HAI Ab Titer^a		Baseline Acute-Phase Neutralizing Ab Titer^a
Characteristic	Patients, No.	Median (IQR)	P^b	Median (IQR)	P^b	Median (IQR)	P^b
Overall	47	7 (5–10)		20 (5–80)		7 (5–40)

Age, y			.42		.75		.90

<50	26	8 (6–12)		28 (5–80)		5 (5–40)

50–64	13	7 (5–9)		14 (5–57)		20 (3–48)

≥65	8	5 (3–9)		20 (5–160)		5 (5–226)

Outcome			.83		.027		.59

Survived	39	7 (5–10)		12 (5–57)		6 (5–40)

Died	8	8 (5–9)		63 (20–226)		20 (5–160)

Abbreviation: IQR, interquartile range.

Overall, 37 patients had a first, baseline blood specimen collected in the acute phase, ≤10 days after symptom onset. Nineteen patients aged <50 years, 11 patients aged 50–64 years, and 7 patients aged ≥65 years had a baseline blood specimen collected in the acute phase. Seven patients who died and 30 patients who survived had a baseline blood specimen collected in the acute phase.

By the 2-sided Kruskal-Wallis test, for differences by patient age, and the Wilcoxon rank sum test, for differences by patient outcome.