A 3-Year Prospective Surveillance Study of Microbiological Isolates among Hematologic Inpatients Shows a High Frequency of Both Community-Acquired and Nosocomial Methicillin-Resistant (MR) and Fluoroquinolone-Resistant (FqR) Strains and the Recent Increase of Enterococci, Viridans Streptococci and Pseudomonaceae with Frequent Antibiotic Multiresistance.

Background. Epidemiological surveillance allows to detect emerging pathogens and antibiotic resistant strains and can provide guideline for an appropriate antibiotic policy. To this end we prospectively analysed all febrile/infectious episodes occurring at our Hematologic Unit during two consecutive 18-month periods from April 2004 to March 2007.

Patients and Methods. Microbiological documented infections (MDI) were considered and correlated with the following variables: diagnosis of acute leukaemia, status of disease, neutropenia (<0.5 × 10^9/L), prophylaxis with levofloxacin, presence of central venous catheter (CVC). An infection was defined nosocomial when recorded after 48h from admission.

Results. Of 773 febrile/infectious episodes during the surveillance period 310 were MDI were and 372 pathogens were isolated. Gram-negative (G−) bacteria represented 49.2% of all pathogens (183/372) and Gram-positive (G+) 41.1% (153/372), fungal pathogens 8.9% (33/372); the proportions remained stable over the two periods. Among G+, Stafilococci (50.3%) and Enterococci (25.5%) were the most frequent bacteria. Stafilococci, particularly S. aureus, were more frequent during the first period (49/76 vs 28/77, p=0.0007 and 27/76 vs 7/77, p<0.0001 respectively), in non neutropenic patients (41/119 vs 36/191, p=0.0028) with uncontrolled disease (60/202 vs 17/108, p=0.0085). Enterococci were more frequent during the second period (14/76 vs 25/77, p=0.06) and in patients with uncontrolled disease (8/108 vs 31/202, p=0.049). Viridans Streptococci occurred almost exclusively during the second period (2.6% vs 14.3%, p=0.017). E. coli (48.6%) and Pseudomonaceae (27.3%) were the most frequent bacteria among G−. E. coli occurred homogenously during the two periods of observation and was associated with neutropenia (64/191 vs 25/119, p=0.02), prophylaxis (57/150 vs 20/93, p=0.007) and presence of CVC (75/237 vs 14/73, p=0.04). Pseudomonaceae increased during the second period (33/97 vs 17/86, p=0.032). MR frequency (68%) was constant during the two periods and was associated with controlled disease (p=0.009) and prophylaxis (p=0.0067). FqR frequency, evaluated for Enterobatteriaceae and Pseudomonas spp (n=123), was 69.3%; it was constant and associated only with levofloxacin prophylaxis (p<0.0001). Vancomicin-resistant Enterococci (VRE) increased during the second period from 21.4% to 32%. Four multiresistant Pseudomonas were observed, all during the last 12 months of observation. Multiresistant strains occurred exclusively as nosocomial infections, whereas there was no statistically significant difference in the frequency of FqR and MR strains between community-acquired and nosocomial isolates.

Conclusions. The high frequency of MR and FqR also among community-acquired infections, as well as the emergence of Enterococci, viridans Streptococci and Pseudomonaceae with antibiotic multiresistance, point to the widespread use of prophylaxis and the inappropriate use of antibiotics as the possible main causative factors which should be reconsidered.