Identification of the transmission vectors of Staphylococcus aureus circulating in a neonatal intensive care unit

Abstract number: P653

Conceicao T., Aires de Sousa M., Barroso R., Paulino E., Sancho L., Brito M., Garrote J., Carreiro H., Machado M., de Lencastre H.

Objectives: The neonatal intensive care unit (NICU) of Hospital Fernando Fonseca, Lisbon, Portugal assists an average of 450 newborns/year and employs 100 healthcare workers (HCW).

Previous reports revealed that in 2002, 22% of the infections at the NICU were due to staphylococci. Identification of the reservoirs and routes of transmission of these microorganisms is a matter of major concern.

Methods: Between July 2005 and June 2007, 10 infection episodes occurred at the NICU. Staphylococcus aureus isolates were recovered during each episode from the infected babies, from nasal swabs of parents and HCW that had contact with the babies, and from the environment. The isolates were characterised by PFGE, spa typing and multilocus sequence typing. Virulence determinants were detected by multiplex PCR.

Results: All but one of the 10 infection episodes (chronologically designated I to X) included a single infected baby. None of the 30 S. aureus strains recovered was resistant to meticillin. Molecular characterisation distributed the 30 MSSA isolates into eight PFGE patterns (A to H). The majority of the isolates (n = 20, 67%) belonged to two major clones: A (spa type t1228 and ST5, n = 11) and B (t012 and ST30, n = 9). Although none of the isolates was PVL positive, all except PFGE pattern B strains were positive for LukE-LukD and gama-hemolisin variant determinants.

In two episodes, isolates belonging to the same PFGE type, but a different subtype, were recovered from both a baby and a HCW (A1, A2 in episode II and B4, B5 in episode X, respectively). No identical isolates from babies and parents and/or environment were found in the same episode. Nevertheless, a HCW isolate from episode II showed the same PFGE subtype (B1) of the babies' isolates in episodes I and VII and a similar type with isolates from babies in episodes VI (B3) and X (B4). However, no direct contact was reported between the four infected babies and this HCW. In addition, in episode VIII the baby was infected with the same strain (PFGE A3) recovered from a HCW and the environment in two anterior episodes (III, VI).

Conclusions: Our data suggests that a S. aureus transmission route could be traced between a HCW and the babies in two infection episodes (II and X). Highly related isolates belonging to two major clones were periodically recovered during epidemiologically unrelated infection episodes, which might indicate that these strains are endemic at the NICU.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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