A new third-generation cephalosporin-resistant Salmonella infantis outbreak in neonatology.

MAYORAL CLARA; ANDRES P.; DI CONZA JOSÉ; GOMEZ M.; RUATTA J.; SCHMELING F.; GUTKIND GABRIEL

Buenos Aires

Congreso; 9th International Congress on Infectious Diseases. Buenos Aires.; 2000

Different third generation cephalosporin-resistant Salmonella serovars have been involved in serious intrahospitalary infection outbreaks (especially in pediatrics and newborn yards) in our region in the past. As their control constitute a difficult challenge for the health system, we analyzed (retrospectively) different aspects of a (beta-lactamase positive) Salmonella Infantis outbreak between April/1997 and August/1998. Different objectives were stated, a- a clean characterization of the strains involved in the outbreak; b- analysis of different factors contributing to their dissemination; c- analysis of the control measures that contribute to clear their presence in the different involved yards. During this period, a total of 681 newborns were admitted, most of them receiving ampicillin and gentamicin since admission. Their stools were examined for the presence of enteropathogens; once the outbreak was detected, samples from their parents and from hospital personnel were also analyzed. Salmonella Infantis could be isolated in 19 patients (no one admitted for any pathology related to gastroenteritis) using SS-agar; they were identified according to the classical Edwards & Ewing´s scheme, serotyped using antisera generously provided by the ANLIS “Carlos Malbrán”. All the patients had been admitted at least ten days before positive cultures; from them, six developed diarrhea. All the isolates displayed the same antibiotype: resistance to ampicillin and ampicillin-sulbactam, first-, second- and third-generation cephalosporins, aztreonam, gentamicin, amikacin and nitrofurantoin; they remained susceptible to fosfomycin, chloramphenicol, trimethoprim-sulfamethoxazole, imipenem and colistin. Beta-lactamase were characterized by means of a combination of different enzymatic and genotypic methods including isoelectric point determinations, hydrolysis profile, PCR with different primers, colony- and dot-blot hybridizations. All strains displayed the presence of a BLEA (TEM-1, pI: 5,4) and a BLEE (CTX-M derived, compatible with CTX-M-2, pI: 8.2). Although all positive patients were treated with fosfomycin, three remained as carriers after treatment. Close vicinity and incubators rotation, congenital malformation, surgical interventions and deficiencies in nursing were all probably associated with bacterial dissemination, complicated by readmission and/or transference to other yards without bacteriological warning of two of the post-treatment carriers. Exhaustive care on hygiene and intestinal decontamination with colistin were part of the measures that helped to control this outbreak.