| Microbe | All children (n = 76)No (%) | Children without preceding antibiotic treatment (n = 37)No (%) | Children with preceding antibiotic treatment (n = 39)*No (%) |
| Bacteria | |||
| Streptococcus pneumoniae† | 35 (46) | 23 (62) | 12 (31)‡ |
| Haemophilus influenzae | 22 (29) | 5 (14) | 17 (44)§ |
| Moraxella catarrhalis | 21 (28) | 11 (30) | 10 (26) |
| Staphylococcus aureus | 9 (12) | 5 (14) | 4 (10) |
| Mycoplasma pneumoniae¶ | 2 (3) | 1 (3) | 1 (3) |
| Other bacteria** | 3 (4) | 2 (5) | 1 (3) |
| Normal/mixed flora | 11 (14) | 5 (14) | 6 (15) |
| Negative | 2 (3) | 0 (0) | 2 (5) |
| Total | 60 (79) | 30 (81) | 30 (77) |
| Viruses | |||
| Rhinovirus | 22 (29) | 13 (35) | 9 (23) |
| Human bocavirus | 14 (18) | 4 (11) | 10 (26) |
| Human metapneumovirus | 10 (13) | 3 (8) | 7 (18) |
| Respiratory syncytial virus | 3 (4) | 0 (0) | 3 (8) |
| Enteroviruses | 2 (3) | 1 (3) | 1 (3) |
| Parainfluenzae type 3 virus | 1 (1) | 1 (3) | 0 (0) |
| Influenza A virus | 1 (1) | 0 (0) | 1 (3) |
| Influenza B virus | 1 (1) | 1 (3) | 0 (0) |
| Adenovirus | 0 (0) | 0 (0) | 0 (0) |
| Parainfluenzae type 1 virus | 0 (0) | 0 (0) | 0 (0) |
| Parainfluenzae type 2 virus | 0 (0) | 0 (0) | 0 (0) |
| Total | 42 (55) | 17 (46) | 25 (64) |
*Antibiotic treatment was as follows: penicillin G, 68%; penicillin G and macrolide or clindamycin, 13%; intravenous cephalosporin, 9%; intravenous cephalosporin and macrolide or clindamycin, 3%; oral amoxicillin or macrolide, 7%. Sputum induction was performed before administration of one intravenous antibiotic dosage in 9 children, after two intravenous antibiotic dosages in 21 children, after three intravenous antibiotic dosages in 3 children and after oral antibiotic treatment in 6 children.
†In one child Streptococcus pneumoniae was also isolated from blood culture.
‡p = 0.006 by χ2 test, comparison between children with preceding antibiotic treatment and those without.
§p = 0.004 by χ2 test, comparison between children with preceding antibiotic treatment and those without.
¶Mycoplasma pneumoniae was detected by PCR.
**Streptococcus agalactie, Streptococcus pyogenes, Pseudomonas-like Gram-negative rod.