Chlamydia trachomatis infections of the female and male genital tracts are often asymptomatic and, thus, tend to become persistent. In the persistent state the typical Chlamydia life cycle is arrested and standard antibiotic regimens do not always eradicate this infection. We sought to relate treatment failures in men and women with persistent chlamydial genital tract infections to electron microscopic evidence of chlamydial persistence and with atypical morphological forms of the organism. Of 16 patients with chlamydial persistence following azithromycin treatment, morphological variants of this organism were observed by electron microscopy from one endocervical sample and one male urethral sample. We document the presence of intracellular inclusions containing only reticulate bodies, extracellular monomembrane and polymembrane phagosomes containing elementary bodies and reticulate bodies with abnormal outer membranes in the process of dividing extracellularly. These observations parallel previous in vitro studies of chlamydial persistence under adverse conditions. This capacity of C. trachomatis to undergo atypical morphological alterations in vivo may contribute to its persistence and relative resistance to antibiotics.

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Page 120, left column, line 1, paragraph 3 from the top and throughout the whole text measeles should read rubella Page 120, right column, line 5, paragraph 1 from the top, the phrase …reversion to the wild type, i.e., hyperattenuation, and the emergence of vaccination linked complications during the creation of vaccines make it necessary… should read reversion to the wild type, hyperattenuation and the emergence of vaccina tion linked complications make it necessary… Page 120, right column, line 17, paragraph 1 from the top, the term full virus vaccine of type 3 should read poliovirus vaccine type 3. Page 121, left column, line 22, paragraph 4 from the top and throughout the whole text the term lgCCID 50 /ml should read logTCD 50 /mL. Page 121, left column, line 24, paragraph 5 from the top, the term amplification into DNA should read amplification of cDNA.