Table 3

 Aetiology determined by routine microbiological research and serological investigation

AetiologyPDT (n = 134)EAT (n = 128)Total (n = 262)
PDT, pathogen directed treatment group; EAT, empirical antibiotic treatment group.
*Nine cases of Legionnaire’s disease (six in the PDT group and three in the EAT group) were the result of a visit to a flower exhibition in Bovenkarspel, the Netherlands.
†Gram negative Enterobacteriaceae: PDT: E coli (2×). EAT, definitive diagnoses: E coli (1×), Enterobacter cloacae (1×). EAT, presumptive diagnoses: E coli (1×), Enterobacter aeruginosa (1×), Klebsiella pneumoniae (1×), Citrobacter freundii (1×), Klebsiellla oxytoca (1×), Morganella morgagnii (1×), E cloacae (1×).
‡PDT: Haemophilus parainfluenzae (2×), Pseudomonas aeruginosa (1×), α-haemolytic streptococcus (1×). EAT, definitive diagnoses: Arcanobacterium haemolyticum (1×) and streptococcus group C (1×). EAT, presumptive diagnoses: P aeruginosa (1×), streptococcus group B (1×), Staphylococcus epidermidis (1×).
¶Mixed infection consisted of a typical bacterial pathogen and a definitive atypical bacterial or viral pathogen.
Streptococcus pneumoniae, n (%)49 (37)43 (34)92 (35)
    Definitive161531
    Presumptive332861
Mycoplasma pneumoniae, n (%)
    Definitive13 (10)10 (8)23 (9)
Haemophilus influenzae, n (%)13 (10)6 (5)19 (7)
    Definitive033
    Presumptive13316
Legionella pneumophila*, n (%)
    Definitive7 (5)7 (5)14 (5)
GNEB†, n (%)2 (1)9 (7)11 (4)
    Definitive022
    Presumptive279
Staphylococcus aureus, n (%)6 (4)4 (3)10 (4)
    Definitive246
    Presumptive404
Moraxella catarrhalis, n (%)
    Presumptive7 (5)07 (3)
Viral infection, n (%)
    Definitive4 (3)6 (5)10 (4)
Chlamydia pneumoniae, n (%)
    Definitive1 (<1)01 (<1)
Other‡, n (%)4 (3)5 (4)9 (3)
    Definitive022
    Presumptive437
Mixed infection¶, n (%)7 (5)10 (8)17 (6)
Unknown, n (%)50 (37)59 (46)109 (42)