Computer analysis of Staphylococcus aureus phage typing data from 1957 to 1975, citing epidemiological trends and natural evolution within the phage typing system.

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RESUMO

Computer analysis of Staphylococcus aureus phage ty ping data collected for over 18 years in a large research hospital showed a drastic decrease in the number of hospital epidemic strains. Phage lysis patterns gradually modified from those of earlier years and were a reflection of changes within the S. aureus reservoir, and not within the typing phages, since the typing phages were used from stable lyophilized stocks. There was increasing cross-lysis of S. aureus strains by phages of lytic groups I, II, and III, such that this grouping was no longer epidemiologically valid. A 61% increase in unique strains occurred from the period 1957 to 1975. Disappearance of the widely recognized epidemic strains was followed by a proliferation of unique strains with individual phage patterns. These increased from 38% in the period 1957 to 1962 to 62% in the period 1969 to 1975, indicating a trend toward a "one patient-one strain" situation. Nontypable strains decreased in more recent years from 16% (1957 to 1975) to 7% in 1978, following introduction of phages 94, 96, 292, and D-11. Pandemic S. aureus strain 80/81 first appeared in this hospital in 1959, 5 years after it was first reported in the United States. Strain 80/81 disappeared from the hospital in 1963, partly due to the advent of methicillin.

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