[The changing patterns and the associated factors of microbial pathogens in ventilator-associated pneumonia in a respiratory intensive care unit from 1995 to 2004].

OBJECTIVE: To investigate the changing patterns and associated factors of microbial pathogens which caused ventilator-associated pneumonia (VAP) in our respiratory intensive care unit (RICU) from 1995 to 2004.

METHODS: Cases of VAP in our RICU from 1995 to 2004 (n = 137) were retrospectively analyzed, 47 cases from 1995 to 1999 and 90 cases from 2000 to 2004. VAP was diagnosed according to the following criteria: pneumonia occurred 48 hours after tracheal intubations; new or progressive infiltrative opacities on chest X ray film; and at least two of the following clinical features: (1) Temperature > 38.0 degrees C or < 35.5 degrees C, (2) WBC > 10 x 10(9)/L or < 4 x 10(9)/L, (3) purulent airway secretions; and positive bacterial cultures (the samples obtained through endotracheal intubations). The data were analyzed using statistical software SPSS version 11.5. Continuous data were expressed as (-x) +/- s. t-test and chi(2)-test were used for continuous and categorical data, respectively. Logistic regression analysis was used to determine the risk factors for special pathogens.

RESULTS: The mean incidence of VAP was 17.9% from 1995 to 2004 (137/765), 16.2% from 1995 to 1999 (n = 47, 3.1% - 29.8%) and 19.6% from 2000 to 2004 (n = 90, 12.4% - 27.7%). From 1995 to 1999, common pathogens were Stenotrophomonas maltophilia (n = 15, 23.4%), Pseudomonas aeruginosa (n = 12, 18.8%), Aerobacter cloacae (n = 8, 12.5%) and Acinetobacter baumanii (n = 7, 10.9%). From 2000 to 2004, common pathogens were Acinetobacter baumanii (n = 40, 34.2%), Pseudomonas aeruginosa (n = 32, 27.4%), Staphylococcus aureus (n = 24, 20.5%) and Stenotrophomonas maltophilia (n = 8, 6.8%). There were 2 cases (2/64, 3.1%) caused by Staphylococcus aureus from 1995 to 1999, and both were caused by Methicillin-resistant Staphylococcus aureus (MRSA); there were 24 cases caused by Staphylococcus aureus from 2000 to 2004, and 21 cases (21/117, 17.9%) were caused by MRSA.There were 11 (11/47, 23.4%) and 45 (45/90, 50.0%) cases with central intravenous catheters in the period of 1995 to 1999 and 2000 to 2004, respectively. In the period of 1995 to 1999 and 2000 to 2004, durations of aerosolized therapy were (46 +/- 55) and (28 +/- 30) days. There were 12 patients (12/47, 25.5%) using second-generation cephalosporin before VAP occurred in the period of 1995 to 1999 and 7 patients (7/90, 7.8%) in the period of 2000 to 2004. There were 13 patients (13/47, 27.7%) using penicillin before VAP in the period of 1995 to 1999 and 10 patients (10/90, 11.1%) in the period of 2000 to 2004. There were 10 patients (10/47, 21.3%) using quinolones before VAP in the period of 1995 to 1999 and 46 patients (46/90, 51.1%)in the period of 2000 to 2004. The occurrence of Staphylococcus aureus VAP may be related to the cross-infection between inpatients (Wald = 16.690, P < 0.01, OR = 9.212). VAP caused by Stenotrophomonas maltophilia was positively related to duration of aerosolized therapy (Wald = 7.852, P < 0.01, OR = 1.021). VAP caused by Acinetobacter baumanii was positively related to third-generation cephalosporin usage (Wald = 5.553, P < 0.05, OR = 3.461).

CONCLUSIONS: The incidence of VAP was not increased in the recent 10 years in our RICU, but the incidence of VAP caused by Acinetobacter baumanii. Staphylococcus aureus and MRSA increased significantly, may be related to the decrease of duration of aerosolized therapy, the usage of different kinds of antibiotics and cross-infection between inpatients.