Evidence of nosocomial Stenotrophomonas maltophilia cross-infection in a neonatology unit analyzed by three molecular typing methods.

OBJECTIVE

To characterize the epidemiological relationships among Stenotrophomonas maltophilia isolates in the neonatology unit of our institution over a 4-month period in which an increased number of isolates was observed.

SETTING

The neonatology ward in a 2,000-bed university hospital in Madrid, Spain.

DESIGN

A retrospective molecular epidemiological analysis using three different typing methods, arbitrarily primed polymerase chain reaction (PCR), pulsed-field gel electrophoresis, and enterobacterial repetitive intergenic consensus-PCR, was performed with 11 isolates obtained from seven neonates over a 4-month period. Presumed unrelated isolates also were included as controls. A similarity dendrogram was obtained, to analyze the genetic relatedness among the isolates.

RESULTS

All isolates from the neonates, except one, showed a remarkably high homology among their typing patterns for the three methods assayed and clustered in the relatedness dendrogram at 96% similarity. The unrelated strains selected as controls were unclustered. The index case was considered to be a newborn who had an S. maltophilia isolate from a culture drawn on the day of admission to the neonatology unit and which was included in the clustered similarity group.

CONCLUSIONS

Such a high genetic similarity among the isolates, together with the presence of an index case who had been colonized or infected by S. maltophilia before arrival at our institution, constitutes the first evidence of nosocomial cross-transmission of this microorganism.