Patients
Among the 1012 children with bronchiolitis identified in this study, one pathogen was detected in 842 (83.2%) children. Among these patients, 603 (71.6%) were male and 239 (28.4%) were female, with ages ranging from 1month to 24 months (median: 5 months). The median duration of symptoms before admission was 6 days. With respect to clinical presentation, 372 (44.2%) had sneezing, 241 (28.6%) had fever, 172 (20.4%) had tachypnea, 51 (6.1%) had dyspnea, and 164 (19.5%) required oxygen administration.
Etiology
The most common pathogens detected were RSV (44.4%), MP (15.6%), HRV (14.4%), HBoV (9.8%), and PIV (8.0%). Coinfection was identified in 137 (13.5%) of the patients. The viruses detected in coinfections were RSV, IV, HRV, HBoV, PIV, hMPV, and ADV. Further, among the patients, 62.3% were ≤ 6 months old; 24% were 6 months to ≤ 1 years old and 13.7% of patients were 1 to 2 years old. The most common pathogens isolated were RSV (58.9%), HRV (11.6%), MP (11.3%), and PIV (8.8%) in patients aged ≤ 6 months. On other hand, in the patients of ages between 6 months and ≤ 1 years, the most common pathogens were RSV (27.7%), MP (22.1%), HBoV (18.6%), and HRV (17.8%). For 1 to 2-year-old children, the most common pathogens were MP (24.3%), HRV (22.2%), RSV (20.1%), and HBoV (18.1%). Thus, for children under 6 months of age, RSV was identified as the most common pathogen responsible for bronchiolitis, while MP infection was less common (all P < 0.002) (Figure 1).
Mixed infections
Of the 842 patients, 614 (72.9%) had single viral infections; 91 (10.8%) had only MP infections; 70 (8.3%) had multiple viral infections, and 67 (8.0%) had viral infection mixed with MP. Among patients aged ≤ 6 months, 12% had coinfection, with 6.5% having multiple viral infections and 5.5% having coinfection of a virus and MP. Among patients between 6 months and ≤ 1 years of age, 22.8% had co-infection, with 11.4% having mixed viral-viral infections and 11.4% having viral-MP infections. In the patients aged 1 to 2 years, 24.3% had co-infection, with 11.3% and 13.0% having mixed viral-viral and viral-MP co-infections, respectively. The probability of coinfection in children of age ≤ 6 months was significantly lower than in children of age between 6 months and ≤ 2 years (all P < 0.002) (Table 1 and Figure2).
Table 1 Pathogens Identified in Hospitalized Children with Bronchiolitis
Pathogen
|
No. of Episodes
|
Total No. of
Episodes
|
Single Infection
|
Coinfection
With Viruses
|
Coinfection
With MP
|
Viruses a
|
|
|
|
|
RSV
|
377 (84.0)
|
43 (9.6)
|
29 (6.4)
|
449
|
HRV
|
86 (58.9)
|
43 (29.5)
|
17 (11.6)
|
146
|
HBoV
|
58 (58.6)
|
29 (29.3)
|
12 (12.1)
|
99
|
PIV
|
61 (75.3)
|
10 (12.3)
|
10 (12.3)
|
81
|
IV
|
16 (45.7)
|
15 (42.9)
|
4 (11.4)
|
35
|
hMPV
|
12 (75.0)
|
1 (6.3)
|
3 (18.8)
|
16
|
ADV b
|
4
|
2
|
1
|
7
|
Atypical pathogen a
|
|
|
|
|
MP
|
91 (57.6)
|
67 (42.4)
|
—
|
158
|
a Data are n (%).
b The percentages are not listed because the total episodes is too small.
Comparisons of clinical characteristics of the patients with single and mix infections
Comparison of the demographic and clinical features of the children shows that children with single virus infection was the youngest (mean age: 5.58 months). Further, the number of children presenting with fever and percentage of neutrophils were the lowest among children infected with a single virus (all P < 0.001). The median duration of symptoms before admission of children with single MP infection (9 days), as well as those with viral-MP infection (7 days) was significantly greater than that of children infected with single virus (5 days) (P < 0.001, respectively). The mean length of stay of children with single virus infection (8.1 days), as well as those with viral-MP infection (8.0 days) was significantly less than that of children infected with viral-MP (9.0 days) (P < 0.05, respectively). Children with single virus infection had a higher rate of oxygen therapy compared with single MP infection (21.7% VS 8.8%, P=0.004), while the PICU admission rate didn’t differ between the two groups. (Table 2).
Table 2 The Demographic and Clinical Characteristics of 842 Patients with Bronchiolitis Associated with Single/Mixed infections
Characteristics
|
Single virus
|
Single MP
|
Mixed viruses
|
Mixed viruses/MP
|
P value
|
No. of patients
|
614
|
91
|
70
|
67
|
—
|
Age, months a
|
5.58cde
|
8.80c
|
7.51d
|
8.12e
|
<0.001
|
Gender, % male
|
72.5
|
67
|
74.3
|
67.2
|
0.560
|
Duration of symptoms before
admission, days b
|
5cd
|
9c
|
7
|
7d
|
<0.001
|
Length of stay b
|
8
|
7
|
8
|
8
|
0.038
|
Fever, %
|
23.6cde
|
40.7 c
|
35.7 d
|
50.7e
|
<0.001
|
Nasal congestion, %
|
45.8
|
31.9
|
41.4
|
49.3
|
0.082
|
Tachypnoea, %
|
21.5
|
13.2
|
20
|
17.9
|
0.303
|
Dyspnea, %
|
6.8
|
2.2
|
5.7
|
4.5
|
0.340
|
WBC count, ×109/L a
|
9.77
|
10.20
|
9.72
|
10.92
|
0.159
|
Percentage of neutrophils a
|
33.3cde
|
39.05c
|
38.46d
|
40.78e
|
<0.001
|
CRP, mg/Lb
|
0.39
|
0.76
|
0.34
|
0.96
|
0.133
|
Need of oxygen, %
|
21.7cd
|
8.8ce
|
11.4d
|
22.4e
|
0.008
|
PICU admission, %
|
10.6
|
5.5
|
10
|
7.5
|
0.429
|
aThe mean value was used.
b The median value was used.
c Significant differences were observed between each pair of values.
d Significant differences were observed between each pair of values.
e Significant differences were observed between each pair of values.