The incidence of Gram-negative bacteremia has increased in hematopoietic stem cell transplant (HSCT) recipients. We prospectively collected data from 13 Brazilian HSCT centers to characterize the epidemiology of bacteremia occurring early post transplant, and to identify factors associated with infection due to multi-drug-resistant (MDR) Gram-negative isolates. MDR was defined as an isolate with resistance to at least two of the following: third-or fourth-generation cephalosporins, carbapenems or piperacillin-tazobactam. Among 411 HSCT, fever occurred in 333, and 91 developed bacteremia (118 isolates): 47% owing to Gram-positive, 37% owing to Gram-negative, and 16% caused by Gram-positive and Gram-negative bacteria. Pseudomonas aeruginosa (22%), Klebsiella pneumoniae (19%) and Escherichia coli (17%) accounted for the majority of Gram-negative isolates, and 37% were MDR. These isolates were recovered from 20 patients, representing 5% of all 411 HSCT and 22% of the episodes with bacteremia. By multivariate analysis, treatment with third-generation cephalosporins (odds ratio (OR) 10.65, 95% confidence interval (CI) 3. 75-30.27) and being at one of the hospitals (OR 9.47, 95% CI 2.60-34.40) were associated with infection due to MDR Gram-negative isolates. These findings may have important clinical implications in the decision of giving prophylaxis and selecting the empiric antibiotic regimen.

We study the influence of the gravitational field of Friedmann geometries upon an electromagnetic potential, through the Proca electromagnetic theory in a Dirac aether. The results are compared with those as foreseen by the Maxwellian theory in curved spacetime. Our findings show that strong amplification effects of electromagnetic fields are a distinctive possibility. Thence we discuss some related topics. * E-mail: alexandr@ov.ufrj.br 541 Mod. Phys. Lett. A 2001.16:541-555. Downloaded from www.worldscientific.com by NORTHEASTERN UNIVERSITY on 02/02/15. For personal use only.

Proca's equations for two types of fields in a Dirac's aether with electric conductivity σ are solved exactly. The Proca electromagnetic fields are assumed with cylindrical symmetry. The background is a static, curved spacetime whose spatial section is homogeneous and has the topology of either the three-sphere S 3 or the projective three-space P 3 . Simple relations between the range of Proca field λ, the Universe radius R, the limit of photon rest mass m γ and the conductivity σ are written down.

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We search for an amplification mechanism of the seed cosmic magnetic induction by studying a new version of the Dirac's aether in a curved cosmological background. We find that the variation of the scale factor R(t) with cosmic time brings to the magnetic field the desired effect of amplification, that we call geometric amplification.

We derive topological algebras for two-dimensional models admitting a dϭ͓␦,b͔ decomposition ͑with b the BRST operator͒. In general, the topological algebra we obtain is not derived from the twisting of an Nϭ2 supersymmetry algebra. We show, for the particular case of an Abelian model described by a ladder of matter, how to derive Nϭ2 supersymmetry generators from the odd generators of the topological algebra.

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