Table 2.

Characteristics of infants with severe bronchiolitis according to profiles (A–D) in three cohort studies.

Patient characteristics*	All	Profiles				P-value
		A	B	C	D
	n = 3081	n = 388 (13%)	n = 1064 (34%)	n = 993 (32%)	n = 636 (21%)
Age (months)						<0.001
<2	31%	13%	22%	37%	49%
2-5.9	42%	35%	48%	43%	36%
6-11.9	26%	52%	29%	20%	15%
Girls	41%	35%	36%	43%	48%	<0.001
Race/ethnicity						<0.001
Non-Hispanic white	45%	43%	44%	45%	48%
Non-Hispanic black	20%	25%	25%	16%	17%
Hispanic	30%	30%	27%	33%	30%
Other	5%	3%	4%	5%	5%
Prematurity (32-37 weeks)	21%	27%	20%	22%	19%	<0.001
Breastfeeding	58%	59%	59%	55%	60%	0.19
Daycare use	18%	18%	24%	16%	12%	<0.001
Number of siblings at home						0.27
0	22%	22%	24%	19%	22%
1	36%	35%	35%	38%	37%
≥2	42%	43%	42%	43%	41%
Maternal smoking during
pregnancy	16%	18%	16%	15%	14%	0.31
Exposure to environmental tobacco
smoke	13%	12%	13%	14%	11%	0.39
Parental history of asthma	32%	35%	34%	29%	30%	0.046
Viral etiology
RSV only	53%	0%	60%	62%	61%	<0.001
Rhinovirus only	7%	47%	0%	1%	4%	<0.001
RSV and rhinovirus	12%	<1%	15%	18%	7%	<0.001
RSV and other non-rhinovirus	9%	0%	12%	12%	7%	<0.001
Rhinovirus and other non-RSV	4%	26%	0%	1%	2%	<0.001
Non-RSV and non-rhinovirus	14%	26%	14%	7%	19%	<0.001
Use of mechanical ventilation	7%	4%	1%	16%	3%	<0.001
Admission to intensive care unit	16%	14%	4%	34%	9%	<0.001
Cohort†						<0.001
MARC-30 USA	-	12%	34%	32%	22%
MARC-35	-	10%	35%	36%	17%
MARC-30 Finland	-	23%	37%	21%	19%

Abbreviations: ED, emergency department; MARC, Multicenter Airway Research Collaboration; RSV, respiratory syncytial virus.

Percentages may not equal 100 because of rounding and missingness.

* The variables used in the latent class analysis are shown in Table 1.

† Row percentages are presented only for the cohort variable.