CHANGING PATTERNS AMONG THE SUBGROUPS OF STRAINS OF STAPHYLOCOCCUS-AUREUS OF PHAGE GROUP-II IN DANISH HOSPITALS FROM 1961-91

During the period 1961-91 a total of 567 635 strains of Staphylococcus aureus from hospitalized patients in Denmark have been characterized according to their antibiotic resistance, site of isolation and phage type. Strains of phage group II (typed by the phages 3A, 3C, 55 and 71 ) have been analysed further. The occurrence of group II strains was r elatively constant (approximately 16%) from 1961 until 1983. Since the n the frequency of group II strains increased; in 1991 they accounted for 22.7% of all S. aureus strains isolated. Strains of group II can, on the basis of their phage types, be divided in four subgroups: 3A, 7 1, 71+ and the 'rest of group II'. Furthermore, within these groups st rains may differ from one another in respect to their sensitivity to p hages. The increased isolation of group II strains during recent years was because of an increase in strains of subgroups 71+ and the 'rest of group II strains'. In 1991 these two subgroups accounted for 89.7% of all group II strains. Furthermore, an increasing number of group II strains, 71.4% in 1991, was typable only at RTD x 100. The increase i n the number of group II strains was even throughout Denmark. All four subgroups of group II have, during the observation period, become mor e frequently resistant to penicillin and/or tetracycline. Strains type d at 100 x RTD of subgroup 71+ and the 'rest of group II' are more fre quently antibiotic resistant than the rest of the group II strains. St rains of the increasing subgroups occurred most often in abscesses.