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Prevention of pseudo-outbreaks requires meticulous use of preventive measures for infection-prone medical procedures.

An outbreak of bacteraemia in a haemodialysis unit where 65 episodes of infection involved 35 outpatients is reported. Burkholderia cepacia complex was the agent most frequently recovered from blood. Thirty-three environmental and clinical isolates of B. cepacia complex were characterized by whole-cell protein electrophoresis and recA-RFLP profile. Fourteen isolates were genomovar I and 16 isolates were not classifiable by their recA-RFLP pattern. Ribotyping, random amplification of polymorphic DNA (RAPD) and integron profile were used to explore the clonality of the isolates, and revealed multiple strain genotypes. Four ribotypes and RAPD types and three integron patterns were identified. The water supply was identified as the source of the outbreak, and inappropriate cleaning and a leak in the reverse osmosis tubing connection were the probable causes of contamination. B. cepacia complex was still recovered from blood of patients even after apparently adequate measures were taken and water quality standards were met, suggesting that higher standards for water quality should be adopted in haemodialysis units. The genomovars recovered here were distinct from those commonly reported for cystic fibrosis isolates.

The integron content of Gram-negative strains implicated in three distinct episodes of suspected cross-infection among inpatients was investigated and compared with ribotyping. In the first episode, ribotyping identified a strain of Acinetobacter, isolated over a 3-month period, responsible for an outbreak associated with the use of mechanical ventilation in the intensive care unit (ICU). The second episode concerned simultaneous isolations of Pseudomonas aeruginosa and Serratia marcescens from 13 bronchoscopy patients. In these two episodes, results obtained by analysis of integron content and ribotyping were in agreement and correctly identified the epidemiologically related strains. In the third episode, isolates of Enterobacter cloacae were collected from patients in the neonatal ICU over a 3-month period. Although several isolates belonged to the same ribotype, cross-infection could not always be confirmed when the integron content was analysed. Integron detection can be considered a useful tool for studying molecular epidemiology in hospital environments, facilitating the quick detection of possible cross-infection cases, especially in critical wards such as the ICU.

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RESUMO: A tipagem molecular do genoma bacteriano, na maioria das vezes, envolve a análise de fragmentos de restrição do DNA cromossômico. Desde que a ribotipagem foi descrita, em 1986, tem sido amplamente utilizada para analisar relações taxonômicas e/ou epidemiológicas entre os diferentes grupos de organismos. A ribotipagem usa o padrão de restrição do opéron de RNA ribossômico (rrn) como ferramenta epidemiológica e tem fornecido ótimos resultados para a detecção de polimorfismo do comprimento dos fragmentos de restrição (RFLPs). O número de opérons rrn da bactéria está diretamente relacionado ao potencial discriminatório da técnica, fornecendo um maior ou menor número de bandas. UNITERMOS: Epidemiologia Molecular. Técnicas para Tipagem de Bactérias. Infecções Bacterianas.

Molecular typing techniques have become increasingly important for confirmation of epidemiological relationships and delimitation of nosocomial outbreaks. The discriminatory power of the two DNA‐based typing methods, conventional ribotyping and ribo‐PCR, was assessed to distinguish between selected strains of Acinetobacter calcoaceticus, Enterobacter cloacae, Serratia marcescens and Pseudomonas aeruginosa. Overall, conventional ribotyping was more discriminatory than ribo‐PCR.

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