Long-term Staphylococcus aureus carrier state in hospital patients.

Staphylococcus aureus colonization of 326 predominantly chronic-care (long-term) patients was studied for 24 years. There were 5,827 upper respiratory cultures positive for S. aureus, ranging from 10 to 88 per patient, determined by the number of years (1 to 21; average, 4.6) that the patient was studied. Patients on the average carried 2.8 S. aureus strains. One patient carried eight strains. Each patient had a predominant strain. Predominant strains tended to be permanent, with 87% persistence over the studied years. Lytic group III strains were more than twice as frequent as group I strains and eight times as frequent as group II strains. Patient carriage of multiple S. aureus strains was usual. A collection of large numbers of cultures over an extended period was necessary for this statistical study, since cultures positive for predominant strains were interspersed with negative cultures and cultures positive for minor strains. Thus, persistence of carriage of a predominant S. aureus strain in a patient continues despite frequent negative cultures and cultures positive for minor strains.