The diagnosis of enteric bacterial pathogens was performed at
the Statens Serum Institut (SSI) or at one of 11 regional clinical
microbiology laboratories in Denmark during 2003 [7]. The SSI
was notified of all positive findings and received all Salmonella
isolates from the external laboratories. Salmonella isolates were
serotyped according to the Kauffmann–White serotyping
scheme [8]. All S. Typhimurium isolates were characterised
further by: (1) antibiotic MICs determined with the Sensititre
system (TREK Diagnostic Systems, East Grinstead, UK); (2)
phage-typing [9]; and (3) pulsed-field gel electrophoresis
(PFGE) analysis using the Pulse-Net standard protocol [10]
with restriction enzyme XbaI. PFGE data were analysed with
BioNumerics software (Applied Maths, Kortrijk, Belgium), and
a UPGMA tree was generated using the Dice similarity
coefficient. Phage-typing was performed at the Danish Institute
for Food and Veterinary Research. Salmonella surveillance
data are published on the Internet in an open-access format
with weekly updates [11]. On suspicion of outbreaks, or when
patients with multidrug-resistant (MDR) S. Typhimurium
isolates (resistant or intermediately susceptible to four or more
classes of antibiotics) are found, the patients and ⁄ or their
treating physicians are contacted by telephone.