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dSerratia marcescens causes health care-associated infections with important morbidity and mortality. Particularly, outbreaks produced by multidrug-resistant isolates of this species, which is already naturally resistant to several antibiotics, including colistin, are usually described with high rates of fatal outcomes throughout the world. Thus, it is important to survey factors associated with increasing frequency and/or emergence of multidrug-resistant S. marcescens nosocomial infections. We report the investigation and control of an outbreak with 40% mortality due to multidrug-resistant S. marcescens infections that happened from November 2007 to April 2008 after treatment with colistin for Acinetobacter baumannii meningitis was started at hospital H1 in 2005. Since that year, the epidemiological pattern of frequently recovered species has changed, with an increase of S. marcescens and Proteus mirabilis infections in 2006 in concordance with a significant decrease of the numbers of P. aeruginosa and A. baumannii isolates. A single pulsed-field gel electrophoresis (PFGE) cluster of S. marcescens isolates was identified during the outbreak. When this cluster was compared with S. marcescens strains (n ‫؍‬ 21) from 10 other hospitals (1997 to 2010), it was also identified in both sporadic and outbreak isolates circulating in 4 hospitals in Argentina. In132::ISCR1::bla CTX-M-2 was associated with the multidrug-resistant cluster with epidemic behavior when isolated from outbreaks. Standard infection control interventions interrupted transmission of this cluster even when treatment with colistin continued in several wards of hospital H1 until now. Optimizing use of colistin should be achieved simultaneously with improved infection control to prevent the emergence of species naturally resistant to colistin, such as S. marcescens and P. mirabilis.

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A twelve-year retrospective review of Staphylococcus aureus infections in adult and pediatric patients (AP and PP respectively) assisted in the Hospital Interzonal General de Agudos Evita in Lanús was performed to determine the incidence, foci of infection, the source of infection and to analyze the profile of antimicrobial resistance. An amount of 2125 cases of infection in AP and 361 in PP were documented. The incidence in AP decreased significantly in the last three years (χ; p<0.05); in PP it increased significantly during the last five years (χ; p<0.0001). In both populations was detected a notable increase in skin infections and associated structures (PEA) in bacteremia to the starting point of a focus on PEA, and in total S. aureus infections of hospital-onset (χ; p < 0.005). Methicillin-resistance (MRSA) increased from 28 to 78% in PP; in AP it remained around 50%, with significant reduction in accompanying antimicrobial resistance to non-β-lactams in both groups of MRSA. In S. aureus documented from community onset infections (CO-MRSA) in the last three years, the percentage of methicillin-resistance was 57% in PP and 37% in AP; in hospital-onset infections it was 43% and 63% respectively. Although data showed that S. aureus remains a pathogen associated with the hospital-onset, there was an increase of CO-MRSA infections with predominance in PEA in both populations.

Introduction: Light-emitting diode fluorescence microscopy (LED-FM) has been endorsed by the World Health Organization (WHO) for tuberculosis diagnosis, but its accuracy in HIV-infected patients remains controversial, and only some few studies have explored procedural factors that may affect its performance. Objective: To evaluate the performance of LED-FM for tuberculosis diagnosis in patients with and without HIV infection using a newer, less expensive LED lamp. Materials and methods:We compared the performance of LED-FM and Ziehl-Neelsen (ZN) microscopy on respiratory specimen smears from tuberculosis (TB) suspects and patients on treatment examined by different technicians blinded for HIV-status and for the result of the comparative test. We analyzed the effect of concentrating specimens prior to microscopy using different examination schemes and user-appraisal of the LED device. Results: Of the 6,968 diagnostic specimens collected, 869 (12.5%) had positive Mycobacterium tuberculosis cultures. LED-FM was 11.4% more sensitive than ZN (p<0.01). Among HIV-positive TB patients, sensitivity differences between LED-FM and ZN (20.6%) doubled the figure obtained in HIVnegative patients or in those with unknown HIV status (9.3%). After stratifying by direct and concentrated slides, the superiority of LED-FM remained. High specificity values were obtained both with LED-FM (99.9%) and ZN (99.9%).The second reading of a sample of slides showed a significantly higher positive detection yield using 200x magnification (49.4 %) than 400x magnification (33.8%) (p<0.05). The LEDdevice had a very good acceptance among the technicians. Conclusion: LED-FM better performance compared with ZN in HIV-infected patients and user-appraisal support the rapid roll-out of LED-FM. Screening at 200x magnification was essential to achieve LED-FM increased sensitivity.

From August 2008 to December 2011, six metallo-β-lactamase-producing isolates, four Enterobacter cloacae, one Klebsiella oxytoca and one Citrobacter freundii, were detected at Hospital Interzonal General de Agudos "Evita" in Lanús. All six isolates showed multiresistant profiles and the presence of the blaIMP-8 gene. Five isolates also expressed PER-2 extended spectrum β-lactamase. The blaIMP-8 gene was found as the first cassette in a class 1 integron. However, the 3´ conserved sequence could not be detected in three isolates. In all cases, blaIMP-8 was transferred by conjugation to azide-resistant Escherichia coli J53. PFGE analysis revealed that the four E. cloacae isolates were not genetically related. These are the first metallo-β-lactamases detected in this institution and our results suggest a possible intra- and inter-species horizontal dissemination of blaIMP-8.