Epidemiology of nosocomial pneumonia in infants after cardiac surgery

BACKGROUND: The pattern of nosocomial pneumonia (NP) in infants in a pediatric surgical ICU after cardiac surgery may differ from that seen in adult ICUs. STUDY OBJECTIVES: The primary aim of this study was to describe the epidemiology of NP in infants after cardiac surgery and, secondarily, to describe the changes of the distribution and antibiotic resistance of the pathogen during the last 3 years. METHODS: Data were collected between June 1999 and June 2002 from 311 consecutive infants who underwent open-heart surgery in our hospital. We retrospectively analyzed the distribution and antibiotic resistance pattern of all the pathogenic microbial isolates cultured from lower respiratory tract aspirations. RESULTS: Of 311 infants, 67 patients (21.5%) acquired NP after cardiac surgery. The incidence of NP was more frequently associated with complex congenital heart defect (CHD) compared to simple CHD (43% vs 15.9%, chi(2) = 22.47, p < 0.0001). The proportion of late-onset NP was higher in patients with complex CHD (chi(2) = 6.02, p = 0.014). A total of 79 pathogenic microbial strains were isolated. Gram-negative bacilli (GNB) were the most frequent isolates (68 isolates, 86.1%), followed by fungi (6 isolates, 7.6%) and Gram-positive cocci (5 isolates, 6.3%). The main GNB were Acinetobacter baumanii (11 isolates, 13.9%), Pseudomonas aeruginosa (10 isolates, 12.7%); other commonly seen GNB were Flavobacterium meningosepticum (7 isolates, 8.9%), Klebsiella pneumoniae (7 isolates, 8.9%), Escherichia coli (6 isolates, 7.6%), and Xanthomonas maltophilia (5 isolates, 6.2%). The most commonly seen Gram-positive cocci were Staphylococcus aureus (2 isolates, 2.5%) and Staphylococcus epidermidis (2 isolates, 2.5%). The frequent fungi were Candida albicans (5 isolates, 6.3%). Most GNB were sensitive to cefoperazone-sulbactum, piperacillin-tazobactam, imipenem, ciprofloxacin, amikacin. The bacteria producing extended spectrum beta-lactamases were mainly from K pneumoniae and E coli; the susceptibility of ESBL-producing strains to imipenem was 100%. There were one case of methicillin-resistant S aureus (MRSA) and 1 case of methicillin-resistant S epidermidis; their susceptibility to vancomycin, gentamycin, and ciprofloxacin were 100%. From 1999 to 2002 in infants with NP after open-heart surgery, there was a trend of increasing frequency of multiresistant GNB such as A baumanii, P aeruginosa, and K pneumoniae. However, no remarkable changes of distribution were found in Gram-positive cocci and fungi in the 3-year period. Early onset episodes of NP were frequently caused by Haemophilus influenzae, methicillin-sensitive S aureus, and other susceptible Enterobacteriaceae. Conversely, in patients who acquired late-onset NP, P aeruginosa, A baumannii, other multiresistant GNB, MRSA, and fungi were the predominant organisms. CONCLUSIONS: The pattern of pathogens and their antibiotic-resistance patterns in NP in infants after cardiac surgery had not shown an increasing prevalence of Gram-positive pathogens as reported by several adult ICUs. GNB still remained the most common pathogens during the last 3 years in our hospital. There was a trend of increasing antibiotic resistance in these isolates.