Typing of meticillin resistant Staphylococcus aureus
(MRSA) by whole genome sequencing (WGS) is performed
routinely in Copenhagen since January 2013.
We describe the relatedness, based on WGS data and
epidemiological data, of 341 MRSA isolates. These
comprised all MRSA (n = 300) identified in Copenhagen
in the first five months of 2013. Moreover, because
MRSA of staphylococcal protein A (spa)-type 304
(t304), sequence type (ST) 6 had been associated with
a continuous neonatal ward outbreak in Copenhagen
starting in 2011, 41 t304 isolates collected in the city
between 2010 and 2012 were also included. Isolates
from 2013 found to be of t304, ST6 (n=14) were compared
to the 41 earlier isolates. In the study, isolates
of clonal complex (CC) 22 were examined in detail,
as this CC has been shown to include the hospitalacquired
epidemic MRSA (EMRSA-15) clone. Finally,
all MRSA ST80 were also further analysed, as representatives
of an important community-acquired MRSA
in Europe. Overall the analysis identified 85 spa-types
and 35 STs from 17 CCs. WGS confirmed the relatedness
of epidemiologically linked t304 neonatal outbreak
isolates. Several non-outbreak related patients
had isolates closely related to the neonatal isolates
suggesting unrecognised community chains of transmission
and insufficient epidemiological data. Only
four CC22 isolates were related to EMRSA-15. No community
spread was observed among the 13 ST80 isolates.
WGS successfully replaced conventional typing
and added information to epidemiological surveillance.
Creation of a MRSA database allows clustering
of isolates based on single nucleotide polymorphism
(SNP) calling and has improved our understanding of
MRSA transmission.