Infection with Chlamydia trachomatis lymphogranuloma venereum serovar L1 in homosexual men with proctitis: molecular analysis of an unusual case cluster.

Among 767 rectal isolates of Chlamydia trachomatis obtained from men over the period 1981-1991, 7 were found to be a rare lymphogranuloma venereum serovar, L1. These isolates were from rectal specimens taken from five male patients in 1982-1983. Six of the seven isolates were available for DNA sequencing studies. All six of these isolates shared the same DNA sequence in the major outer membrane protein (MOMP) gene variable domains and had different MOMP sequences than did the prototype L1, L2, and L3 strains, suggesting a point source outbreak. All five patients infected with serovar L-1 were homosexual men who had symptomatic proctitis characterized by rectal pain, discharge, tenesmus, abnormalities seen on anoscopy, and leukocytes seen on gram stains of rectal specimens. We conclude that an unrecognized point source outbreak of the rare chlamydial L1 serovar occurred among homosexual men in Seattle in 1982-1983, and that the clinical manifestations of L1 infection may be less severe than those of L2 infections.