The molecular epidemiology of three biotypes of Corynebacterium diphtheriae in the Seattle outbreak, 1972-1982.

Between 1972 and 1982 Seattle experienced a diphtheria outbreak involving 1,100 cases, primarily adults with cutaneous lesions. Biotyping revealed three consecutive overlapping outbreaks including 433 toxinogenic intermedius cases. Isolates from each quarter year were examined for DNA restriction fragment patterns and hybridization patterns with three DNA probes. All intermedius outbreak isolates appeared identical in all analyses and most stock cultures had the outbreak DNA fragment pattern, but DNA probes detected six patterns within 11 intermedius stock cultures. The mitis outbreak was heterogeneous, involving at least five restriction fragment patterns. In contrast, DNA restriction fragment analyses indicated that 22 of 25 gravis outbreak isolates belonged to a single strain, whereas there were seven strains within eight gravis stock cultures. DNA probe analyses of gravis outbreak isolates detected seven different patterns, five involving copy numbers of the toxB fragment and attB sites that presumably reflected lysogenic events that occurred during the outbreak.