Over 500 medical students have been examined for nasal carriage of Staph. pyogenes at weekly intervals over a period ranging from 3 to 12 months.
Nasal carriers were classified as persistent, intermittent and occasional. Of the students, 39% were persistent or intermittent carriers in whom the staphylococcus was believed to colonize the skin of the vestibule of the nose; 42% were occasional carriers in whom the staphylococcus was only a chance inhabitant of the nares.
Staph. pyogenes was isolated from the anterior nares of persistent carriers on at least 90% of the occasions on which they were examined, and was of the same phage type on each occasion. From intermittent carriers it was isolated less regularly, but on at least 10% of occasions on which they were examined, and it remained of one phage type. Staph. pyogenes was isolated at less than 10% of swabbings from occasional carriers, and at each the organism was of a different phage type.
Eighty-nine per cent of persistent and intermittent carrier strains, and 54% of occasional carrier strains could be typed with phage filtrates. The strains not typable with phage filtrates, and found predominantly among occasional carriers, were considered worthy of separate classification, and it is suggested that typability with phage be used as a criterion of pathogenicity for Staph. pyogenes.
We wish to thank Prof. T. J. Mackie for his continued interest and advice; Dr J. P. Duguid for criticism and advice; Dr R. E. O. Williams and Miss Joan Rippon of the Staphylococcal Reference Laboratory, Colindale, who very kindly instructed one of us (J.C.G.) in bacteriophage typing; Dr Donald Cruickshank for taking nasal swabs from patients; Dr Cumming of the Blood Transfusion Department, Royal Infirmary, Edinburgh, for permission to swab blood donors, and the medical students who so willingly co-operated in this work.