PCR-based assays were used to evaluate agr locus nucleotide polymorphism for the identification of agr autoinducer receptor specificity groups within a population of Staphylococcus aureus isolates colonizing children and their guardians. All isolates could be assigned to one of three major agr groups that had similar prevalences, regardless of whether isolates were implicated in transmission of S. aureus within families. Among healthy carriers, agr groups I to III appear to be equally fit, which may reflect selection for the coexistence of S. aureus strains in a population.

HIV-infected injection-drug users have progression to AIDS at rates comparable to those of other HIV-infected groups, but they have substantial pre-AIDS morbidity and mortality, particularly from bacterial infections, which also appear to predict disease progression.