Hospitalization for Influenza A Versus B

Article Figures & Data

TABLE 1

Distribution of Hospital Admissions by Influenza Type and Season

TABLE 2

Characteristics of Hospitalized Patients by Influenza Type

Characteristics	Influenza Type^a
Characteristics	Influenza A (n = 2645)	Influenza B (n = 1510)	Unadjusted OR/P
Boys	1554 (58.8)	875 (57.9)	0.97 (0.85–1.10)
Age, y
Mean (SD)	3.4 (3.9)	5.0 (4.3)	<.0001
Median (IQR)	2.0 (0.6–4.8)	3.9 (1.4–7.2)	<.0001
Age group			<.0001
0–5 mo	586 (22.2)	170 (11.3)	—
6–23 mo	749 (28.3)	305 (20.2)	—
24–59 mo	681 (25.7)	423 (28.0)	—
5–9 y	406 (15.3)	401 (26.6)	—
≥10 y	223 (8.4)	211 (14.0)	—
Health status			.0004
No underlying condition	1342 (50.7)	684 (45.3)	—
Vaccine-indicated condition	976 (36.9)	651 (43.1)	—
Other underlying condition	327 (12.4)	175 (11.6)	—
Ethnic origin^b
White	532/845 (63.0)	337/591 (57.0)	—
Asian	92/845 (10.9)	60/591 (10.2)	—
Middle Eastern	51/845 (6.0)	45/591 (7.6)	—
Black	49/845 (5.8)	74/591 (12.5)	—
Latin American	17/845 (2.0)	11/591 (1.9)	—
Aboriginal	81/845 (9.6)	46/591 (7.8)	—
Other/mixed	23/845 (2.7)	18/591 (3.0)	—
Data not available	675	419	—
Influenza vaccination status^c
Received influenza vaccine	98/1504 (6.5)	59/855 (6.9)	—
Data not available	555	485	—

—, Inferential statistical analysis was not conducted.
↵a Data are n (column %) unless otherwise indicated; where fractions are shown, denominator is the number of cases with data available.
↵b Data available only for 2008–2009 season onward; n = 1520 (influenza A), n = 1010 (influenza B).
↵c Includes children ≥6 mo; n = 2059 (influenza A), n = 1340 (influenza B).

TABLE 3

Signs and Symptoms of Hospitalized Patients by Influenza Type

Sign or Symptom^a	Influenza Type^b
Sign or Symptom^a	Seasonal A (n = 2142)	Influenza B (n = 1248)	Unadjusted OR	Adjusted OR^c
Systemic
Fever	1990 (92.9)	1167 (93.5)	1.10 (0.83–1.46)	—
Headache	78 (3.6)	123 (9.9)	2.89 (2.16–3.88)	1.85 (1.36–2.52)
Lethargy	741 (34.6)	465 (37.3)	1.12 (0.97–1.30)	—
Respiratory
Coryza	1277 (59.6)	744 (59.6)	1.00 (0.87–1.15)	—
Cough	1835 (85.7)	1051 (84.2)	0.89 (0.73–1.08)	—
Wheezing	476 (22.2)	260 (20.8)	0.92 (0.78–1.09)	—
Respiratory distress	904 (42.2)	489 (39.2)	0.88 (0.76–1.02)	—
Apnea	65 (3.0)	37 (3.0)	0.98 (0.65–1.47)	—
Extrarespiratory
Abdominal pain	119 (5.6)	126 (10.1)	1.91 (1.47–2.48)	1.38 (1.05–1.81)
Vomiting and/or diarrhea and/or dehydration	1003 (46.8)	569 (45.6)	0.95 (0.83–1.10)	—
Myalgia	38 (1.8)	102 (8.2)	4.93 (3.37–7.20)	3.19 (2.16–4.72)
Arthralgia	10 (0.5)	15 (1.2)	2.59 (1.16–5.79)	1.95 (0.86–4.40)
Seizure	238 (11.1)	116 (9.3)	0.82 (0.65–1.04)	—

—, adjusted OR was not calculated.
↵a Individuals had >1 sign or symptom and percentages do not add up to 100%.
↵b Data are n (column %) unless otherwise indicated; data available only for 2006–2007 season onward.
↵c Adjusted for age group and health status.

TABLE 4

Treatment and Illness Severity of Hospitalized Patients by Influenza Type

Treatment	Influenza Type^a
Treatment	Seasonal A (n = 2645)	Influenza B (n = 1510)	Unadjusted OR/P	Adjusted OR/P^b
Antiviral
Antibiotic	400/2643 (15.1)	202/1508 (13.4)	0.87 (0.72–1.04)	—
Measures of illness severity	1913/2640 (72.5)	1050/1508 (69.6)	0.87 (0.76–1.00)	—
Respiratory complications
Croup	101 (3.8)	51 (3.4)	0.88 (0.62–1.24)	—
Pneumonia (radiologically confirmed)	595 (22.5)	364 (24.1)	1.09 (0.94–1.27)	—
Extrarespiratory complications
Myositis	18 (0.7)	101 (6.7)	10.46 (6.31–17.35)	6.95 (4.15–11.64)
Myocarditis	6 (0.2)	6 (0.4)	1.75 (0.56–5.45)	—
Hepatitis	24 (0.9)	22 (1.5)	1.61 (0.90–2.89)	—
Meningitis	6 (0.2)	4 (0.3)	1.17 (0.33–4.15)	—
Encephalitis	42 (1.6)	36 (2.4)	1.51 (0.97–2.37)	—
Length of hospital stay, median (IQR), d	3.0 (2.0–5.0)	3.0 (2.0–5.0)	0.60	—
Mortality
Attributable to influenza	10 (0.4)	16 (1.1)	2.82 (1.28–6.23)	2.65 (1.18–5.94)
All-cause	10 (0.4)	18 (1.2)	3.18 (1.46–6.90)	2.95 (1.34–6.49)
Admitted to ICU	337 (12.7)	190 (12.6)	0.99 (0.82–1.19)	—
Required mechanical ventilation^c	212 (62.9)	124 (65.3)	1.11 (0.76–1.61)	—
Required extracorporeal membrane oxygenation^c	7 (2.1)	6 (3.2)	1.54 (0.51–4.64)	—
Length of ICU stay, median (IQR), d^c	3.0 (1.0–6.5)	3.0 (1.0–7.0)	0.62	—

—, adjusted OR or P was not calculated.
↵a Data are n (column %) unless otherwise indicated; where fractions are shown, denominator is the number of cases with data available.
↵b Adjusted for age group and health status.
↵c Denominator of the percentage is the number of ICU admitted cases.

TABLE 5

Factors Associated With Radiologically Confirmed Pneumonia in Patients Hospitalized With Influenza B

	Radiologically Confirmed Pneumonia
	Univariate Analysis (n = 1510)		Multivariable Analysis^a (n = 1510)
	OR (95% CI)	P	OR (95% CI)	P
Boys	0.94 (0.74–1.20)	.63	—	—
Age, y	0.98 (0.95–1.01)	.13	—	—
Age group		<.0001		<.0001
0–5 mo	Reference		Reference
6–23 mo	3.29 (1.94–5.57)	<.0001	2.88 (1.69–4.91)	<.0001
24–59 mo	3.33 (2.00–5.54)	<.0001	2.66 (1.58–4.47)	.0002
5–9 y	1.75 (1.03–2.98)	.04	1.40 (0.82–2.40)	.22
≥10 y	2.03 (1.15–3.60)	.01	1.48 (0.82–2.66)	.19
Health status		<.0001		<.0001
No underlying condition	Reference		Reference
Vaccine-indicated condition	1.95 (1.51–2.52)	<.0001	1.93 (1.47–2.51)	<.0001
Other underlying condition	1.27 (0.85–1.90)	.25	1.25 (0.83–1.89)	.28

—, sex and age (in years) were not included in the multivariable model.
↵a Multivariable model included age group and health status as independent variables.

TABLE 6

Factors Associated With ICU Admission in Patients Hospitalized With Influenza B

	Univariate Analysis (n = 1510)		Univariate Analysis by Health Status^a
			No Underlying Condition (n = 684)		Vaccine-Indicated Condition^b (n = 651)		Other Underlying Condition (n = 175)
	OR (95% CI)	P	OR (95% CI)	P	OR (95% CI)	P	OR (95% CI)	P
Boys	1.13 (0.83–1.54)	.44	—^c	—^c	—^c	—^c	—^c	—^c
Age, y	1.03 (0.99–1.06)	.10	—^c	—^c	—^c	—^c	—^c	—^c
Age group		.05		.01		.13		.59
0–5 mo	Reference		Reference	—	Reference	—	Reference	—
6–23 mo	1.28 (0.70–2.35)	.42	3.46 (1.26–9.49)	.02	0.33 (0.11–0.96)	.04	0.43 (0.11–1.70)	.23
24–59 mo	1.46 (0.82–2.58)	.20	2.64 (0.95–7.35)	.06	0.47 (0.18–1.21)	.12	0.62 (0.17–2.26)	.47
5–9 y	0.97 (0.53–1.77)	.92	1.70 (0.57–5.01)	.34	0.29 (0.11–0.78)	.01	0.57 (0.16–2.08)	.40
≥10 y	1.91 (1.04–3.54)	.04	5.79 (1.91–17.57)	.002	0.41 (0.15–1.13)	.08	1.13 (0.29–4.44)	.86
Health status		.002
No underlying condition	Reference		—^d	—^d	—^d	—^d	—^d	—^d
Vaccine-indicated condition	1.68 (1.20–2.35)	.003	—^d	—^d	—^d	—^d	—^d	—^d
Other underlying condition	2.00 (1.25–3.21)	.004	—^d	—^d	—^d	—^d	—^d	—^d

↵a Conducted due to detection of an interaction between age group and health status (P = .045) on multivariable analysis.
↵b For the 0–5 mo age group, a vaccine-indicated condition refers to an underlying condition for which influenza vaccination is particularly recommended in individuals aged ≥6 mo, and does not indicate that influenza vaccination should be given to this age group.
↵c Sex and age (in years) were not included in the multivariable model.
↵d N/A.