multistrain outbreak of chancroid in san francisco 19891991 restriction fragment length polymorphism rflp and plasmid analyses were used to evaluate an outbreak of haemophilus ducreyi in san francisco fiftyfour cases of cultureconfirmed chancroid occurred between may 1989 and may 1991 of these 46 96 were in men and 35 65 were in blacks the median age of patients was 34 years among the 32 isolates submitted for rflp and plasmid analyses six different hindiii rflp patterns were identified two rflp types were found in patients who had recently traveled to los angeles korea or el salvador four rflp types appeared to be acquired locally and were more common among blacks p 002 in patients with a history of a sexually transmitted disease p 01 and in those who used drugs or exchanged drugs or money for sex p 08 the use of rflp analysis confirmed that this outbreak was associated with multiple strains of h ducreyi and allowed for the identification of risk factors for locally acquired chancroid