Table 3. Isolated pathogens causing hospital-acquired pneumonia and correlation to previous colonization of trachea, pharynx or stomach.

Microorganism	HAP n (mean time in days)/(range)	Previous colonization (%)	LAT mean time in days/(range)
Pseudomonas aeruginosa	13 (7.0)/(3-12)	6 (46)	1.8 (1-3)
Klebsiella pneumoniae	8 (6.4)/(4-10)	6 (75)	4.8 (4-5)
Klebsiella spp.	4 (7.3)/(6-9)	4 (100)	2.8 (1-4)
Enterobacter spp.	5 (6.8)/(4-12)	5 (100)	3.6 (2-8)
Acinetobacter calcoaceticus	4 (10.8)/(8-16)	4 (100)	4.8 (4-5)
Haemophilus influenzae	4 (3.8)/(3-5)	1 (25)	1.0 (1)
Escherichia coli	2 (8.0)/(8)	1 (50)	5.0 (5)
Proteus mirabilis	1 (3)/(3)	0	0
Gram-negative	41 (7.5)/(3-16)	27 (65.9)	2.9 (1-6)
Staphylococcus aureus	10 (5.5)/(3-11)	7 (70)	2.9 (1-5)
MRSA	2 (5.5)/(4-7)	1 (50)	2.0 (2)
Streptococcus pneumoniae	2 (3.0)/(3)	1 (50)	2.0 (2)
Gram-positive	14 (5.9)/(3-11)	9 (64.3)	2.7 (1-5)
Total	55 (7.1)/(3-16)	36 (65.5)	2.8 (1-6)

HAP = hospital-acquired pneumonia; LAT = latency time between colonization and development of pneumonia; MRSA = methicillin resistant Staphylococcus aureus