Objective: To determine if molecular epidemiologic techniques, including comparative automated DNA sequencing of polymorphic virulence genes, could be used in the course of a bacterial disease outbreak to unambiguously determine clonal relationships among implicated strains.
Design: Strains recovered from all patients with invasive infections and a sample of carriers were analyzed by multilocus enzyme electrophoresis and automated DNA sequencing of a gene encoding an extracellular protease and a highly polymorphic part of the streptokinase gene.
Setting: A US Air Force training facility in San Antonio, Tex.
Patients: A squadron with about 800 Air Force trainees, including three recruits with invasive Streptococcus pyogenes infections.
Results: Multilocus enzyme electrophoresis and automated DNA sequencing of polymorphic virulence genes unambiguously defined person-to-person spread of an otherwise rare S pyogenes clone in the course of the disease outbreak and clarified strain relationships in real time.
Conclusions: Molecular strain characterization techniques can be employed rapidly in a disease outbreak to definitively resolve complex relationships among pathogenic bacteria, infer patterns of clone spread, and help formulate rational public health control measures. The approach has broad applicability to other infectious agents.