Background
Methods
Setting, data collection, and linkage
Data sources
National Registry of hospital care
Statistical analysis
Results
General descriptives
Main analyses (n = 676)
Hospitalization
Total group (n = 676) | Probable and certain term infants (n = 596)a | Certain term infants (n = 388)b | Preterm infants (n = 80) | |
---|---|---|---|---|
Characteristics of hospitalization, clinical course, and treatment | ||||
Boys; n (%)1 | 335 (49.6%) | 295 (49.5%) | 185 (47.7%) | 40 (50%) |
Age in months at admittance; median (range) | 2.0 (0–36) | 2.0 (0–35) | 2.0 (0–35) | 3.0 (0–25)c,d |
Duration of hospitalization in days; median (range) | 5.0 (1–51) | 5.0 (1–51) | 5.0 (1–51) | 6.0 (1–49) |
Admission intensive care unit (ICU); n (%) | 69 (10.2%) | 59 (9.9%) | 50 (12.9%) | 10 (12.5%) |
Duration ICU stay in days; median (range) | 9 (2–34) | 9 (2–25) | 9 (2–25) | 15 (8–34)c,d |
Vaccinated at admission; n (%) | 250/541 (46.2%) | 213/481 (44.3%) | 130/319 (40.7%) | 37/60 (61.7%)c,d |
Coughing attacks; n (%) | 494 (73.1%) | 438 (73.5%) | 280 (72.2%) | 56 (70.0%) |
Apnea; n (%) | 110 (16.3%) | 92 (15.4%) | 71 (18.3%) | 18 (22.5%) |
Whooping; n (%) | 24 (3.6%) | 23 (3.9%) | 18 (4.6%) | 1 (1.3%) |
Vomiting; n (%) | 238 (35.2%) | 210 (35.2%) | 146 (37.6%) | 28 (35.0%) |
Prolonged inspiratory effort; n (%) | 49 (7.3%) | 42 (7.1%) | 33 (8.5%) | 7 (8.8%) |
Collapse; n (%) | 8 (1.2%) | 6 (1.0%) | 5 (1.3%) | 2 (2.5%) |
Cyanosis; n (%) | 284 (42.0%) | 259 (43.5%) | 176 (45.4%) | 25 (31.3%)c,d |
Fever; n (%) | 60 (8.9%) | 52 (8.7%) | 33 (8.5%) | 8 (10.0%) |
Feeding problems; n (%) | 212 (31.4%) | 185 (31.0%) | 133 (34.3%) | 27 (33.8%) |
Any complicatione; n (%) | 63 (9.3%) | 53 (8.9%) | 39 (10.1%) | 10 (12.5%) |
Antibiotics before admissionf; n (%) | 131/657 (19.9%) | 114/580 (19.7%) | 66/377 (17.5%) | 18/77 (23.4%) |
Antibiotics during admissiong; n (%) | 543/674 (80.5%) | 475/587 (80.9%) | 313/382 (81.9%) | 68/78 (87.2%) |
Intravenous antibiotics during admission; n (%) | 12/403 (3.0%) | 9/357 (2.5%) | 6/244 (2.5%) | 3/46 (6.5%) |
Antibiotic use in days; median (range) | 6 (0–28) | 6 (0–28) | 5 (0–28) | 5.5 (1–18) |
Artificial respiration; n (%) | 50/654 (7.7%) | 39/577 (6.8%) | 32/375 (8.5%) | 11/77 (14.3%)c |
Additional oxygen; n (%) | 226/661 (34.2%) | 198/585 (33.9%) | 150/382 (39.3%) | 28 (36.8%) |
Symptoms remaining; n (%) | 518 (76.6%) | 460 (77.2%) | 298 (76.8%) | 58 (72.5%) |
Re-admittance <6w after discharge; n (%) | 94 (14.0%) | 85 (14.3%) | 56 (14.4%) | 9 (11.4%) |
Diagnostics | ||||
Pertussis test: culture, PCR and serology; n (%) | 34 (5.0%) | 31 (5.2%) | 24 (6.2%) | 3 (3.8%) |
Pertussis test: culture and PCR; n (%) | 59 (8.7%) | 52 (8.7%) | 40 (10.3%) | 7 (8.8%) |
Pertussis test: PCR and serology; n (%) | 84 (12.4%) | 73 (12.2%) | 41 (10.6%) | 11 (13.8%) |
Pertussis test: culture and serology; n (%) | 24 (3.6%) | 24 (4.0%) | 17 (4.4%) | 0 (0%) |
Pertussis test: culture; n (%) | 37 (5.5%) | 29 (4.9%) | 18 (4.6%) | 8 (10%) |
Pertussis test: PCR; n (%) | 329 (48.7%) | 290 (48.7%) | 194 (50%) | 39 (48.8%) |
Pertussis test: serology; n (%) | 69 (10.2%) | 61 (10.2%) | 36 (9.3%) | 8 (10%) |
Unknown diagnostic test for pertussis; n (%) | 40 (5.9%) | 36 (6.0%) | 18 (4.6%) | 4 (5%) |
Result white blood cell counting; n (%) | 225/476 (47.3%) | 200/421 (47%) | 141/276 (51.1%) | 25/55 (45%) |
White blood cell count; median (range) | 17.2 (4.3–106.1) | 17.7 (5.3–106.1) | 17.2 (5.3–74.3) | 13.5 (4.3–64.0) |
Result C-reactive protein; n (%) | 142/392 (36.2%) | 119/344 (35%) | 81/231 (35.1%) | 23/48 (48%) |
C-reactive protein; median (range) | 5 (0–415) | 4.7 (0–415) | 5 (0–415) | 15 (0–363)c,d |
Positive co-infectionsh; n (%) | 81/355 (22.8%) | 63/306 (20.6%) | 46/208 (22.1%) | 18/49 (36.7%)c,d |
Specification of prescribed antibiotics before admission | ||||
Amoxicillin | 49/132 (37%) | 38/114 (33%) | 23/66 (35%) | 11/18 (65%) |
Azithromycin | 24/132 (18%) | 21/114 (18%) | 17/66 (26%) | 3/18 (18%) |
Ceftriaxone | 1/132 (1%) | 1/114 (1%) | 1/66 (2%) | 0/0 |
Clarithromycin | 41/132 (31%) | 38/114 (33%) | 17/66 (26%) | 3/18 (18%) |
Erythromycin | 7/132 (5%) | 6/114 (5%) | 2/66 (3%) | 1/18 (6%) |
Feneticillin | 1/132 (1%) | 1/114 (1%) | 1/66 (2%) | 0/0 |
Trimethoprim | 1/132 (1%) | 1/114 (1%) | 1/66 (2%) | 0/0 |
unknown | 7/132 (5%) | 8/114 (7%) | 4/66 (6%) | 0/18 (0%) |
Specification of prescribed antibiotics during admission | ||||
Amoxicillin | 11/543 (2%) | 10/475 (2%) | 7/313 (2%) | 1/68 (1%) |
Azithromycin | 170/543 (31%) | 146/475 (31%) | 98/313 (31%) | 24/68 (35%) |
Cephotaxim | 1/543 (0.2%) | 0/0 | 0/0 | 1/68 (1%) |
Clarithromycin | 314/543 (58%) | 280/475 (59%) | 184/313 (59%) | 34/68 (50%) |
Erythromycin | 44/543 (8%) | 37/475 (8%) | 23/313 (7%) | 7/68 (10%) |
unknown | 3/543 (0.6%) | 2/475 (0.4%) | 1/313 (0.3%) | 1/68 (1%) |
Specification of reported complications | ||||
conjunctivitis | 5 (0.7%) | 5 (0.8%) | 1 (0.3%) | 0 (0%) |
convulsion | 5 (0.7%) | 5 (0.8%) | 4 (1.0%) | 0 (0%) |
encephalopathy | 1 (0.2%) | 1 (0.2%) | 1 (0.3%) | 0 (0%) |
pneumonia | 11 (1.6%) | 9 (1.5%) | 7 (1.8%) | 2 (2.5%) |
otitis media | 1 (0.2%) | 1 (0.2%) | 0 (0%) | 0 (0%) |
death | 2 (0.3%) | 2 (0.3%) | 2 (0.5%) | 0 (0%) |
bradycardia | 8 (1.2%) | 7 (1.2%) | 6 (1.6%) | 1 (1.3%) |
cardio-respiratory insufficiency | 7 (1.0%) | 5 (0.8%) | 4 (1.0%) | 2 (2.5%) |
desaturation | 20 (3.0%) | 18 (3.0%) | 14 (3.6%) | 2 (2.5%) |
feeding problems | 5 (0.7%) | 2 (0.3%) | 0 (0%) | 3 (3.8%) |
weight loss | 12 (1.8%) | 11 (1.9%) | 8 (2.1%) | 1 (1.3%) |
dehydration | 1 (0.2%) | 1 (0.2%) | 1 (0.3%) | 0 (0%) |
need for drip-feed | 4 (0.6%) | 2 (0.3%) | 1 (0.3%) | 2 (2.5%) |
gastroenteritis | 3 (0.4%) | 2 (0.3%) | 2 (0.5%) | 1 (1.3%) |
sepsis | 1 (0.2%) | 1 (0.2%) | 0 (0%) | 0 (0%) |
extreme high white blood cell count | 2 (0.3%) | 1 (0.2%) | 0 (0%) | 1 (1.3%) |
metabolic alkalosis | 1 (0.2%) | 1 (0.2%) | 0 (0%) | 0 (0%) |
hypotonia | 2 (0.3%) | 1 (0.2%) | 1 (0.3%) | 1 (1.3%) |
Clinical course and treatment
Diagnostics
Total group (n = 676) | Probable and certain term infants (n = 596)a | Certain term infants (n = 388)b | Preterm infants (n = 80) | |
---|---|---|---|---|
Respiratory syncytial virus | 21% (62/293) | 19% (49/257) | 20% (34/169) | 36% (13/36)c,d |
Influenzavirus | 34% (38/112) | 31% (29/93) | 35% (22/62) | 47% (9/19) |
Adenovirus | 36% (35/98) | 33% (27/82) | 35% (18/51) | 50% (8/16) |
Human metapneumovirus | 35% (28/81) | 32% (22/68) | 32% (12/37) | 46% (6/13) |
parainfluenzavirus | 33% (25/76)) | 28% (18/65) | 28% (12/43) | 64% (7/11)c,d |
Rhinovirus | 57% (40/70) | 56% (33/59) | 63% (25/40) | 64% (7/11) |
Mycoplasma pneumoniae | 29% (19/65) | 27% (15/55) | 30% (10/33) | 40% (4/10) |
Bocavirus | 56% (9/16) | 42% (5/12) | 44% (4/9) | 100% (4/4) |
Chlamydophila pneumoniae
| 41% (12/29) | 48% (12/25) | 60% (9/15) | 0% (0/4) |
Chlamydia psittaci
| 0% (0/1) | 0% (0/1) | not tested | not tested |
Cytomegalovirus | 33% (4/12) | 22% (2/9) | 33% (2/6) | 67% (2/3) |
Coronavirus | 56% (18/32) | 50% (14/28) | 56% (9/16) | 100% (4/4) |
Coxiella burnetii
| 0% (0/7) | 0% (0/6) | 0% (0/4) | 0% (0/1) |
Enterovirus | 39% (9/23) | 42% (8/19) | 40% (6/15) | 25% (1/4) |
Haemophilus influenzae
| 75% (3/4) | 75% (3/4) | 100% (3/3) | not tested |
Klebsiella oxytoca
| 100% (1/1) | not tested | not tested | 100% (1/1) |
Klebsiella pneumoniae
| 100% (2/2) | 100% (1/1) | 100% (1/1) | 100% (1/1) |
Legionella
| 43% (3/7) | 50% (3/6) | 60% (3/5) | 0% (0/1) |
Moraxella catarrhalis
| 100% (5/5) | 100% (4/4) | 100% (3/3) | 100% (1/1) |
Bordetella parapertussis
| 0% (0/5) | 0% (0/3) | 0% (0/3) | 0% (0/2) |
Parechovirus | 0% (0/3) | 0% (0/2) | 0% (0/2) | 0% (0/1) |
Streptococcus pneumoniae
| 100% (3/3%) | 100% (1/1) | 100% (1/1) | 100% (2/2) |
Influence of coinfections and age at hospitalization on the clinical picture
Probable and certain term infants (n = 596)a,b | Preterm infants (n = 80)b | Crude OR (95% CI) | Adjusted OR (95% CI)c | |
---|---|---|---|---|
Symptoms at admission | ||||
Coughing attacks | 438 (73.5%) | 56 (70.0%) | 0.8 (0.5–1.4) | 0.8 (0.5–1.4) |
Apnea | 92 (15.4%) | 18 (22.5%) | 1.6 (0.9–2.8) |
1.8 (1.0–3.3)
|
Whooping | 23 (3.9%) | 1 (1.3%) | 0.3 (0.04–2.4) | 0.3 (0.04–2.3) |
Vomiting | 210 (35.2%) | 28 (35.0%) | 1.0 (0.6–1.6) | 1.0 (0.6–1.6) |
Prolonged inspiratory effort | 42 (7.1%) | 7 (8.8%) | 1.3 (0.5–2.9) | 1.2 (0.5–2.7) |
Collapse | 6 (1.0%) | 2 (2.5%) | 2.5 (0.5–12.7) | 3.8 (0.7–19.7) |
Cyanosis | 259 (43.5%) | 25 (31.3%) | 0.6 (0.4–1.0) | 0.7 (0.4–1.1) |
Fever | 52 (8.7%) | 8 (10.0%) | 1.2 (0.5–2.6) | 0.9 (0.4–2.0) |
Feeding problems | 185 (31.0%) | 27 (33.8%) | 1.1 (0.7–1.9) | 1.1 (0.7–1.9) |
Complications | ||||
Any complication | 53 (8.9%) | 10 (12.5%) | 1.5 (0.7–3.0) | 1.6 (0.8–3.4) |
Treatment | ||||
Antibiotics before admission | 114/580 (19.7%) | 18/77 (23.4%) | 1.1 (0.6–2.0) | 1.1 (0.6–1.9) |
Antibiotics during admission | 475/587 (80.9%) | 68/78 (87.2%) | 1.5 (0.7–3.2) | 1.8 (0.9–3.9) |
Artificial respiration | 39/577 (6.8%) | 11/77 (14.3%) |
2.3 (1.1–4.8)
|
2.8 (1.3–6.0)
|
Additional oxygen | 198/585 (33.9%) | 28 (36.8%) | 1.1 (0.7–1.9) | 1.3 (0.8–2.2) |
Admission intensive care unit (ICU) | 59 (9.9%) | 10 (12.5%) | 1.3 (0.6–2.7) | 1.6 (0.8–3.6) |
Discharge | ||||
Symptoms remaining | 460 (77.2%) | 58 (72.5%) | 0.8 (0.5–1.3) | 0.8 (0.5–1.4) |
Influence of vaccination and vaccine effectiveness (VE)
Probable and certain term infants (n = 481)a | Preterm infants (n = 60) | |||||||
---|---|---|---|---|---|---|---|---|
Unvaccinated infants (n = 268) | Vaccinated infants (n = 213) | crude OR (95% CI) | adjusted OR (95% CI)b | Unvaccinated infants (n = 23) | Vaccinated infants (n = 37) | crude OR (95% CI) | adjusted OR (95% CI)b | |
Symptoms at admission | ||||||||
Coughing attacks | 197 (73.5%) | 151 (70.9%) | 0.9 (0.6–1.3) | 0.8 (0.4–1.3) | 17 (73.9%) | 26 (70.3%) | 0.8 (0.3–2.7) | 0.8 (0.1–5.6) |
Apnea | 47 (17.5%) | 22 (10.3%) |
0.5 (0.3–0.9)
| 0.6 (0.3–1.1) | 10 (43.5%) | 5 (13.5%) |
0.2 (0.06–0.7)
| 0.2 (0.03–1.5) |
Whooping | 6 (2.2%) | 12 (5.6%) | 2.6 (0.96–7.1) | 1.8 (0.5–6.8) | 1 (4.4%) | 0 | < 0.001 (< 0.001- > 999.9) | 0.4 (< 0.001- > 999.9) |
Vomiting | 94 (35.1%) | 79 (37.1%) | 1.1 (0.8–1.6) | 0.9 (0.6–1.6) | 8 (34.8%) | 13 (35.1%) | 1.0 (0.3–3.0) | 0.6 (0.1–3.3) |
prolonged inspiratory effort | 15 (5.6%) | 19 (8.9%) | 1.7 (0.8–3.3) | 1.0 (0.4–2.3) | 1 (4.4%) | 4 (10.8%) | 2.7 (0.3–25.4) | 1.6 (0.1–26.1) |
Collapse | 2 (0.8%) | 2 (0.9%) | 1.3 (0.2–9.0) | 7.2 (0.2–226.7) | 1 (4.4%) | 1 (2.7%) | 0.6 (0.04–10.3) | 0.6 (< 0.001- > 999.9) |
Cyanosis | 126 (47.0%) | 88 (41.3%) | 0.8 (0.6–1.1)c | 1.1 (0.7–1.8)c | 5 (21.7%) | 17 (45.9%) | 3.1 (0.9–10.0)c | 1.9 (0.3–11.6)c |
Fever | 17 (6.3%) | 21 (9.9%) | 1.6 (0.8–3.1) | 0.7 (0.3–1.7) | 2 (8.7%) | 4 (10.8%) | 1.3 (0.2–7.6) | > 999.9 (< 0.001- > 999.9) |
Feeding problems | 87 (32.5%) | 63 (29.6%) | 0.9 (0.6–1.3) | 0.9 (0.5–1.4) | 10 (43.5%) | 12 (32.4%) | 0.6 (0.2–1.8) | 0.8 (0.2–4.5) |
Complications | ||||||||
Any complication | 30 (11.2%) | 9 (4.2%) |
0.4 (0.2–0.8)
| 0.9 (0.4–2.5) | 5 (21.7%) | 3 (8.1%) | 0.3 (0.07–1.5) | 0.2 (0.01–4.6) |
Treatment | ||||||||
Antibiotics before admission | 37 (14.2%) | 52 (25.1%) |
1.8 (1.2–2.8)
| 1.2 (0.7–2.1) | 2 (9.5%) | 9 (24.3%) | 2.7 (0.6–11.4) | 12.3 (0.8–188.3) |
Antibiotics during admission | 230 (87.5%) | 157 (74.4%) |
0.4 (0.3–0.7)
| 0.7 (0.4–1.3) | 21 (95.5%) | 32 (86.5%) | 0.3 (0.03–2.8) | 1.7 (0.1–23.7) |
Artificial respiration | 23 (8.9%) | 5 (2.4%) |
0.3 (0.1–0.7)
| 0.8 (0.2–3.4) | 7 (31.8%) | 2 (5.6%) |
0.1 (0.02–0.7)
| 0.4 (0.02–5.7) |
Additional oxygen | 133 (50.4%) | 33 (15.9%) |
0.2 (0.1–0.3)
|
0.3 (0.2–0.5)
| 13 (59.1%) | 10 (27.8%) |
0.2 (0.08–0.8)
| 0.6 (0.09–4.0) |
Admission intensive care unit (ICU) | 42 (15.7%) | 5 (2.4%) |
0.1 (0.05–0.3)
| 0.3 (0.1–1.1) | 6 (26.1%) | 2 (5.4%) |
0.2 (0.03–0.9)
| 0.6 (0.04–7.6) |
Discharge | ||||||||
Symptoms remaining | 206 (76.9%) | 162 (76.1%) | 0.9 (0.6–1.3) | 0.7 (0.5–1.2) | 14 (60.9%) | 30 (81.1% | 1.9 (0.7–5.1) | 2.1 (0.7–6.7) |
Term infants | Preterm infants | |||||
---|---|---|---|---|---|---|
Age in months↓ | Vaccinated at admission % (n) | Coverage in general population | Vaccine effectiveness (95% CI)a | Vaccinated at admission % (n) | Coverage in general population | Vaccine effectiveness (95% CI)a |
Main analysis | ||||||
0 m | 0% (0/1) | na | na | 0% (0/1) | na | na |
1 m | 1.4% (2/144) | 1.9% | na | 0% (0/14) | 1.3% | na |
2 m | 34.2% (52/152) | 90.9% | 95%b (93–96%) | 60% (9/15) | 84.9% | 73%b (20–91%) |
3 m | 85.9% (67/78) | 98.8% | 93% (85–96%) | 86.7% (13/15) | 97.9% | 86% (9–96%) |
4 m | 93.8% (30/32) | 99.4% | 91% | 100% (4/4) | 99.4% | na |
Sensitivity analysis | ||||||
0 m | 0% (0/1) | na | na | 0% (0/1) | na | na |
1 m | 0.9% (1/115) | 1.9% | na | 0% (0/14) | 1.3% | na |
2 m | 33.7% (33/98) | 90.9% | 95%b (92–97%) | 60% (9/15) | 84.9% | 73%b (20–91%) |
3 m | 89.4% (42/47) | 98.8% | 90% (71–96%) | 86.7% (13/15) | 97.9% | 86% (9–96%) |
4 m | 100% (14/14) | 99.4% | na | 100% (4/4) | 99.4% | na |