The decline of methicillin resistance among Danish Staphylococcus aureus strains.
OBJECTIVE
To describe the occurrence and decline of methicillin-resistant Staphylococcus aureus in Denmark from 1966 to 1986, and to illustrate why it has been possible to retain a frequency of only 0.2% MRSA since 1984.


METHODS
A study of antibiotic susceptibility and phage-type of 522,978 S aureus strains isolated from hospitalized patients in Denmark during the years 1960 to 1988 combined with clinical information on patients with methicillin-resistant strains during the years 1986 through 1988.


METHODS
All strains and information were collected at the centralized, national laboratory for S aureus phage-typing.


METHODS
Hospitalized patients with S aureus isolates, and especially patients with methicillin-resistant strains.


METHODS
Antibiotic treatment.


RESULTS
The frequency of MRSA rose to 15% in the years 1967 through 1971 but decreased to 0.2% in 1984, and has remained so ever since. The increase was due mainly to the spread of a single or a few clones of the phage-type complex 83A. Occurrence of strains of these phage-types declined from 18% in 1969 to 0.6% in 1989. In 1986 through 1988, at least 48% of the MRSA strains were imported by patients from abroad. Cross-infection occurred only in two cases. High awareness and special precautions were taken when MRSA was detected.


CONCLUSIONS
MRSA of a single or a few clones spread in Danish hospitals in the years 1967 through 1971. Since 1984, only 0.2% of the Danish S aureus population has been MRSA, and imported MRSA strains have been prevented from spreading.
Rosdahl
V T
VT
Staphylococcus Laboratory, Statens Seruminstitut, Copenhagen, Denmark.
Knudsen
A M
AM
D000293:Adolescent; D000328:Adult; D000368:Aged; D001434:Bacteriophage Typing; D002648:Child; D002675:Child, Preschool; D003428:Cross Infection / Q000382:microbiology / Q000635:transmission; D003718:Denmark; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D016106:Methicillin Resistance; D008875:Middle Aged; D013045:Species Specificity; D013211:Staphylococcus aureus / Q000145:classification*