Background
Methods
Study design, setting, participants, and data sources
Cross linkage of the data sources
Statistical analysis
Study approval
Results
Incidence and risk factors of hospitalization for bronchiolitis
Person years (PY) | Cases | Rate (per 100 PY) | 95% CI | |
---|---|---|---|---|
Age (months) | ||||
[0 -- 6]
| 986 | 88 | 8.93 | 7.24 -11.00 |
(6 - 12]
| 1005 | 42 | 4.18 | 3.09 -5.65 |
(12 - 18]
| 921 | 7 | 0.76 | 0.36 -1.59 |
Calendar month
| ||||
January
| 223 | 25 | 11.20 | 7.57 -16.57 |
February
| 226 | 24 | 10.64 | 7.13 -15.87 |
March
| 227 | 14 | 6.18 | 3.66 -10.43 |
April
| 229 | 12 | 5.23 | 2.97 -9.21 |
May
| 235 | 4 | 1.70 | 0.64 -4.54 |
June
| 238 | 3 | 1.26 | 0.41 -3.90 |
July
| 245 | 2 | 0.82 | 0.20 -3.27 |
August
| 251 | 3 | 1.20 | 0.39 -3.71 |
September
| 254 | 3 | 1.18 | 0.38 -3.66 |
October
| 257 | 12 | 4.67 | 2.65 -8.22 |
November
| 262 | 18 | 6.88 | 4.33 -10.91 |
December
| 266 | 17 | 6.39 | 3.98 -10.29 |
Year of observation
| ||||
2000
| 138 | 7 | 5.07 | 2.42 -10.63 |
2001
| 399 | 17 | 4.26 | 2.65 -6.85 |
2002
| 427 | 22 | 5.15 | 3.39 -7.82 |
2003
| 436 | 30 | 6.88 | 4.81 -9.84 |
2004
| 503 | 18 | 3.58 | 2.25 -5.68 |
2005
| 527 | 23 | 4.36 | 2.90 -6.56 |
2006
| 481 | 20 | 4.16 | 2.68 -6.44 |
Total
| 2912 | 137 | 4.70 | 3.98 -5.56 |
N | Person Years (PY) | Cases | Rate (per 100 PY) | 95% CI | ||
---|---|---|---|---|---|---|
Age of the mother (years)
| ≤ 32
| 1119 | 1359.4 | 68 | 5.00 | 3.94 -6.34 |
>32
| 1288 | 1553.1 | 69 | 4.44 | 3.51 -5.63 | |
Parity
|
0
| 1457 | 1773.2 | 77 | 4.34 | 3.47 -5.43 |
1
| 679 | 807.77 | 45 | 5.57 | 4.16 -7.46 | |
≥ 2
| 271 | 331.55 | 15 | 4.52 | 2.73 -7.50 | |
Years of education
| ≤ 8
| 1085 | 1312.5 | 80 | 6.10 | 4.90 -7.59 |
>8
| 1318 | 1597 | 56 | 3.51 | 2.70 -4.56 | |
Unknown
| 4 | 3 | 1 | 33.33 | 4.70 -236.64 | |
Birth-country of the mother
|
Italy
| 2049 | 2505 | 119 | 4.75 | 3.97 -5.68 |
Other
| 358 | 407 | 18 | 4.42 | 2.79 -7.02 | |
Gender
|
Males
| 1282 | 1535.2 | 85 | 5.54 | 4.48 -6.85 |
Females
| 1125 | 1377.3 | 52 | 3.78 | 2.88 -4.95 | |
Birth weight (grams)
| <1000
| 152 | 161.96 | 15 | 9.26 | 5.58 -15.36 |
1000-2000
| 786 | 911.71 | 60 | 6.58 | 5.11 -8.48 | |
>2000
| 1469 | 1838.8 | 62 | 3.37 | 2.63 -4.32 | |
Gestational age
| <32
| 516 | 585.24 | 34 | 5.81 | 4.15 -8.13 |
32-35
| 1891 | 2327.3 | 103 | 4.43 | 3.65 -5.37 | |
Apgar score
| ≤ 7
| 395 | 456 | 36 | 6.57 | 4.74 -9.11 |
>7
| 2012 | 2456 | 101 | 3.43 | 2.82 -4.17 | |
Broncho dysplasia
|
No
| 2346 | 2850 | 131 | 4.60 | 3.87 -5.46 |
Yes
| 61 | 63 | 6 | 9.54 | 4.29 -21.24 | |
Congenital heart disease
|
No
| 2373 | 2873 | 134 | 4.66 | 3.94 -5.52 |
Yes
| 34 | 40 | 3 | 7.58 | 2.44 -23.50 |
CIRR (95% CI) | p-value | AIRR (95% CI) | p-value | ||
---|---|---|---|---|---|
Age of the mother (years)
| ≥ 32 vs. <32
| 1.13 (0.80 -1.58) | 0.49 | 1.08 (0.75 -1.55) | 0.67 |
Parity
|
1 vs. 0
| 1.28 (0.88 -1.86) | 0.19 | 1.34 (0.91 -1.98) | 0.14 |
≥ 2 vs. 0
| 1.04 (0.59 -1.83) | 0.89 | 1.09 (0.60 -1.95) | 0.78 | |
Years of education
| ≤ 8 vs. >8
| 1.74 (1.23 -2.46) | <0.01 | 1.71 (1.18 -2.48) | 0.01 |
Not known vs. >8
| 9.51 (0.88 -102.1) | 0.06 | 9.82 (0.79 -122.4) | 0.08 | |
Birth country of the mother
|
Italy vs. other
| 1.07 (0.65 -1.78) | 0.78 | 1.30 (0.73 -2.30) | 0.37 |
Gender
|
male vs female
| 1.47 (1.03 -2.08) | 0.03 | 1.48 (1.04 -2.10) | 0.03 |
Calendar year (ref. 2001)
| 2000 | 1.19 (0.49 -2.86) | 0.70 | 0.79 (0.33 -1.88) | 0.60 |
2002 | 1.21 (0.64 -2.28) | 0.56 | 1.28 (0.68 -2.43) | 0.44 | |
2003 | 1.61 (0.89 -2.93) | 0.12 | 1.73 (0.95 -3.16) | 0.07 | |
2004 | 0.84 (0.43 -1.63) | 0.61 | 0.92 (0.47 -1.79) | 0.81 | |
2005 | 1.02 (0.54 -1.92) | 0.94 | 1.24 (0.66 -2.34) | 0.50 | |
2006 | 0.98 (0.51 -1.87) | 0.94 | 1.16 (0.60 -2.24) | 0.66 | |
Age (months)
|
<6 vs. ≥ 12
| 11.75 (5.44 -25.35) | <0.01 | 14.54 (6.75 -31.35) | <0.01 |
6-11 vs. ≥ 12
| 5.50 (2.47 -12.24) | <0.01 | 5.98 (2.68 -13.35) | <0.01 | |
Epidemic period
|
Yes vs. No
| 5.89 (3.44 -10.06) | <0.01 | 5.48 (3.22 -9.35) | <0.01 |
Birth weight
|
per 100 g decrease
| 1.05 (1.02 -1.07) | <0.01 | 1.06 (1.02 -1.11) | 0.01 |
Gestational age
|
per 1 week less
| 1.08 (1.02 -1.14) | 0.01 | 0.97 (0.88 -1.07) | 0.58 |
Apgar score
| ≤ 7 vs. > 7
| 2.06 (1.40 -3.03) | <0.01 | 1.57 (0.99 -2.48) | 0.05 |
Broncho-dysplasia
|
Yes vs. No
| 2.08 (0.91 -4.75) | 0.08 | 1.70 (0.68 -4.28) | 0.26 |
Congenital heart disease
|
Yes vs. No
| 1.63 (0.51 -5.18) | 0.41 | 1.64 (0.52 -5.19) | 0.40 |
Use of Palivizumab and estimates of its effectiveness on the risk of hospitalization for bronchiolitis
Yes
| p value | AOR | (95%CI) | p value | |||
---|---|---|---|---|---|---|---|
N
| % | ||||||
Age of the mother (years)
| ≤ 32 (REF)
| 118 | 10.5 | <0.01 | 1.00 | <0.01 | |
>32 | 206 | 16.0 | 1.67 | (1.22 -2.30) | |||
Parity
|
0 (REF)
| 221 | 15.2 | <0.01 | - | ||
1 | 72 | 10.6 | 0.83 | (0.58 -1.18) | 0.30 | ||
>1 | 31 | 11.4 | 0.92 | (0.55 -1.54) | 0.74 | ||
Years of education of the mother
| ≤ 8 years (REF)
| 137 | 12.6 | 0.20 | 1.00 | - | |
>8 years
| 186 | 14.1 | 1.14 | (0.84 -1.54) | 0.42 | ||
Not known
| 1 | 25.0 | NE | - | |||
Country of birth of the mother
|
Italy (REF)
| 283 | 13.8 | 0.23 | 1.00 | - | <0.01 |
Other
| 41 | 11.4 | 0.47 | (0.30 0.73) | |||
Gender
|
Male (REF)
| 160 | 12.5 | 0.13 | 1.00 | - | |
Female
| 164 | 14.6 | 1.34 | (1.00 1.80) | 0.05 | ||
Year of birth
|
2000 (REF)
| 9 | 2.8 | <0.01 | 1.00 | - | |
2001 | 22 | 7.0 | 2.48 | (1.02 -6.00) | 0.04 | ||
2002 | 41 | 13.0 | 7.00 | (3.05 -16.02) | <0.01 | ||
2003 | 47 | 13.0 | 9.37 | (4.13 -21.28) | <0.01 | ||
2004 | 73 | 18.4 | 13.88 | (6.23 -30.93) | <0.01 | ||
2005 | 61 | 18.3 | 17.90 | (7.87 -40.67) | <0.01 | ||
2006 | 71 | 19.1 | 18.43 | (8.19 -41.46) | <0.01 | ||
Birth weight (grams)
|
<1000 (REF)
| 76 | 50.0 | <0.01 | 1.00 | - | |
1000-2000
| 209 | 26.6 | 1.22 | (0.75 -1.99) | 0.42 | ||
>2000 | 39 | 2.6 | 0.18 | (0.10 -0.34 | <0.01 | ||
Gestational age (weeks)
|
<32 (REF)
| 221 | 42.8 | <0.01 | 1.00 | - | |
32-35 | 103 | 5.4 | 0.19 | (0.13 -0.27) | <0.01 | ||
Bronchodysplasia
|
Yes (REF)
| 41 | 67.2 | <0.01 | 5.96 | (2.90 -12.26) | <0.01 |
No
| 283 | 12.1 | - | ||||
Apgar score
| ≤ 7
| 128 | 32.4 | <0.01 | 1.55 | (1.10 -2.19) | 0.01 |
>7 (REF)
| 196 | 9.7 | - | ||||
Month of birth
|
Jan-Mar
| 71 | 12.6 | <0.01 | 1.57 | (1.00 -2.45) | 0.05 |
Apr-Jun (REF)
| 68 | 11.4 | 1.00 | - | |||
Jul-Sep
| 99 | 15.3 | 2.00 | (1.32 -3.03) | <0.01 | ||
Oct-Dec
| 86 | 14.4 | 2.12 | (1.38 -3.26) | <0.01 | ||
Congenital heart disease (CHD)
|
Yes (REF)
| 0 | 0.0 | 0.02 | 1.00 | - | |
No
| 324 | 13.6 | NE | - | |||
Total
| 324 | 13.5 |
Vaccination-dose effectiveness | Vaccination-strategy effectiveness | |||||
---|---|---|---|---|---|---|
IRR | 95% CI | p-value | IRR | 95% CI | p-value | |
Model 1: univariate analysis
| 1,37 | 0,60 -3,11 | 0,45 | 0,82 | 0,40 -1,69 | 0,59 |
Model 2: multiple analysis*
| 0,51 | 0,22 -1,17 | 0,11 | 0,47 | 0,23 -0,98 | 0,04 |
Model 3: as model 2 but restricted to GA<32 weeks
| 0,67 | 0,24 -1,85 | 0,44 | 0,65 | 0,26 -1,63 | 0,36 |
Model 4: as model 2 but restricted only to the epidemic period
| 0,50 | 0,22 -1,14 | 0,10 | 0,49 | 0,24 -1,03 | 0,06 |