chla·​myd·​ia klə-ˈmi-dē-ə How to pronounce chlamydia (audio)
plural chlamydiae klə-ˈmi-dē-ˌē How to pronounce chlamydia (audio)
: any of a genus (Chlamydia, family Chlamydiaceae) of spherical gram-negative intracellular bacteria
especially : one (C. trachomatis) that causes or is associated with various diseases of the eye and urogenital tract including trachoma, lymphogranuloma venereum, cervicitis, and some forms of urethritis
: a disease or infection caused by chlamydiae
chlamydial adjective

Examples of chlamydia in a Sentence

Recent Examples on the Web The surge has been driven largely by the spread of chlamydia, a devastating bacterial infection. Emily Anthes Chang W. Lee, New York Times, 15 Apr. 2024 Some of the most common STIs are HPV, chlamydia, gonorrhea and herpes. Kristen Rogers, CNN, 14 Apr. 2024 Rates of chlamydia, gonorrhea and syphilis in people ages 55 and up more than doubled in the U.S. over the 10-year period from 2012 to 2022, according to data from the Centers for Disease Control and Prevention. Aria Bendix, NBC News, 27 Mar. 2024 Syphilis cases rose by 34% from the previous year, to more than 35,000, and chlamydia cases by 16% to more than 216,000. Fox News, 7 Mar. 2024 According to data from San Mateo County, in the last quarter of 2023, local chlamydia cases increased 11% among men and 7% among women, totaling 1,995 cases. Ryan MacAsero, The Mercury News, 27 Feb. 2024 The treatment was more effective against chlamydia and syphilis than gonorrhea. Sara Reardon, Scientific American, 6 Oct. 2023 In the United States, more than 2.5 million cases of syphilis, gonorrhea, and chlamydia were reported in 2022, according to the Centers for Disease Control and Prevention, a number that has been relatively stable for years. Frances Vinall, Washington Post, 7 Feb. 2024 That could be a sign of an STI such as trichomoniasis, chlamydia, or gonorrhea, or of the infection bacterial vaginosis (BV). Mara Santilli, SELF, 26 Jan. 2024

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'chlamydia.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


borrowed from New Latin, originally the name of a group, from Greek chlamyd-, chlamýs "mantle, chlamys" + New Latin -ia -ia entry 1

Note: The taxon Chlamydia was originally assigned to a group of microorganisms neither bacterial nor viral by Helen Jones, Geoffrey Rake, and Barbara Stearns in "Studies on lymphogranuloma venereum III. The action of the sulfonamides on the agent of lymphogranuloma venereum," Journal of Infectious Diseases, vol. 76, issue 1 (January, 1945), pp. 55-69. The choice of the element chlamyd- was presumably based on the earlier taxon Chlamydozoa (with -zoa -zoa) originated by Ludwig Halberstädter and Stanislaus von Prowazek, "Über Zelleinschlüsse parasitärer Natur beim Trachom," Arbeiten aus dem Kaiserlichen Gesundheitsamte, vol. 26, Heft 1 (1907), pp. 44-47.

First Known Use

1966, in the meaning defined at sense 1

Time Traveler
The first known use of chlamydia was in 1966

Dictionary Entries Near chlamydia

Cite this Entry

“Chlamydia.” Dictionary, Merriam-Webster, Accessed 18 May. 2024.

Medical Definition


chla·​myd·​ia klə-ˈmid-ē-ə How to pronounce chlamydia (audio)
capitalized : the type genus of the family Chlamydiaceae comprising coccoid to spherical gram-negative intracellular parasitic bacteria and including one (C. trachomatis) that causes or is associated with various diseases of the eye and genitourinary tract including trachoma, lymphogranuloma venereum, cervicitis, and some forms of nongonococcal urethritis
plural chlamydiae -ē-ˌē, -ˌī How to pronounce chlamydia (audio) also chlamydias
: a bacterium of the genus Chlamydia
: an infection or disease caused by a bacterium of the genus Chlamydia
chlamydial adjective

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