| Ventilator-associated pneumonia (VAP) is one of the most serious complications in mechanically ventilated patients that develop≥48 h after the patient has been placed on mechanical ventilation (MV). Pseudomonas aeruginosa (PA) is the most common isolates in late onset pneumonia which developed beyond the 4th day of ventilation, associated with the worst morbidity and mortality rates in the neonatal intensive care units (NICU). The pathophysiology of a patient's pulmonary colonization with PA is still unclear:its main origin seems to be endogenous but the contaminated device, environment, and the colonized patients have been clearly shown to be a source and to be involved in horizontal transmission. PA VAP has rarely been reported in NICU. Based on understanding of colonization pathogenesis, rational strategies for nosocomial pneumonia prophylaxis can be instituted. The routes and patterns of colonization or infection with PA and associated risk factors, essential to design appropriate prevention strategies, has rarely been exploited by active surveillance studies.Objective 1.To investigate the respective contribution of endogenous and exogenous transmission of PA in the respiratory colonization or/and infection in the mechanically ventilated patients at a NICU;2. To investigate the distribution of drug resistance of PA;3. To identify routes of lung infection with PA;4. To assess risk factors for colonization or respiratory infection with PA; These findings may be important for the design preventive strategies from PA colonization and pulmonary infection in NICUMethodsA 6-months surveillance prospective survey was performed from January 2009 through June 2009. Samples from oropharyngeal swab, tracheobronchial aspirates, gastric aspirate, and rectal swab were obtained in each patient just before ventilation and then two times per week. Surveillance cultures for the presence of PA from environmental surfaces of the NICU were taken once every five days during the study period. To analyze the predisposing factors for developing VAP due to PA, the following variables were recorded:demographic characteristics, history of prior hospitalizations and antimicrobial use, prior barbiturate use, diagnosis, clinical features, prior trauma or surgery, daily ventilator settings, the duration of MV prior to the development of VAP or colonization, and respiratory procedures during ICU stay. For each colonized or infected patient, a chronological analysis of the isolation was performed. Antibiotic susceptibility was determined by the disk-diffusion method and interpreted according to NCCLS guidelines. The following antibiotics were tested: ceftazidime (CAZ), cefepime (FEP), piperacillin (PIP), piperacillin/tazobactam (TZP), amikacin (AMK), cefoperazone (CFP), cefoperazone/sulbactam (SPF), mezlocillin (MEZ), ciprofloxacin (CIP), imipenem (IMP), meropenem (MER) and levofloxaxin(LVX).Antibiotyping, IRS-PCR and PFGE indicated the epidemiological relationship. Patterns were analyzed as recommended by Tenover et al. Infections showing clinical symptoms and positive cultures at 48 hours or more after birth were defined as NI. Colonization was defined as the isolation of PA from specimens taken from any body site studied without clinical or bacteriologic evidence of infection. To determine the risk factors associated with PA colonization/infection in the mechanically ventilated patients, a case-control study was carried out, with cases involving PA colonized and/or infected neonates and controls, those without colonization by PA, and infection by any microorganism. Potential risk factors were analyzed by univariate and multivariate analysis. To test the independence of the risk factors for PA colonization/infection, the significant variables(p<0.1) in the univariate analyses were entered into a multivariate logistic regression model with forward selection of independent variables. The software package SPSS12.0 was used for the analysis.Results1. During the study period of the 129 patients on mechanically ventilation was more than four days,41 (31.8%) PA colonization proved, among which 10 (7.8%) were already colonized before ventilation. Thus 31 (24.0%) patients were classified as acquired colonized and included in this study.8 patients presented VAP caused by PA. The incidence of PA VAP on the unit was 6.2%. The mean period of MV prior to the VAP onset was 9±3.4 days.2. The sensitivity to amikacin, levofloxacin, ciprofloxacin, piperacillin/tazobactam, cefoperazone/sulbactam, imipenem and meropenem was respectively over70.0%. PAE was inferior sensitivity to piperacillin, mezlocillin, cefoperazone and ceftazidime. The positive rates of gene encoding extended-spectrumβ-lactamase TEM, CRAB, VIM, IMP and FOX were 55.0%,25.0%,15.0%,15.0% and 5.0%; other P-lactamase genes were absent in all isolates.2. In our study 18 of 23 patients (78.3%) had colonization of the upper respiratory tract. The respiratory tract in 8 patients with VAP had been colonized previously by the same strain; simultaneous digestive tract colonization was found in three cases. Neither the stomach nor the rectum as the only initial site of colonization in any case was found.3. Molecular characterizations of 71 PA isolates including 54 clinical strains and 17 environmental strains were performed by PFGE and IRS-PCR. Genotyping analysis 17 unrelated patterns were revealed by PFGE and 18 by IRS-PCR (Table 2).16 (69.6%) patients with colonization of the respiratory tract come from other patients or environmental surfaces were considered exogenous, whereas among strains causing pulmonary infection,4 (50%) strains were of exogenous.4. Birth weight<1500g (OR,6.830), MV≥8 days (OR,3.324), previous ampicillin group (OR,3.631) and second generation cephalosporins use (OR,4.550) were independently associated with PA colonization/infection (p<0.05).ConclusionsOur results confirm the upper respiratory tract act as an important reservoir of PA colonization and infection in the mechanically ventilated patients and emphasize the importance of exogenous acquisition of PA. A combination of early identification and eradication of airways colonization by PA plus infection control measures may be the basis to prevent pulmonary infection.
|
PDF Full Text Request