title: Higher organism load associated with failure of azithromycin to treat rectal chlamydia.
abstract: Repeat rectal chlamydia infection is common in men who have sex with men (MSM) following treatment with 1 g azithromycin. This study describes the association between organism load and repeat rectal chlamydia infection, genovar distribution, and efficacy of azithromycin in asymptomatic MSM. Stored rectal chlamydia-positive samples from MSM were analysed for organism load and genotyped to assist differentiation between reinfection and treatment failure. Included men had follow-up tests within 100 days of index infection. Lymphogranuloma venereum and proctitis diagnosed symptomatically were excluded. Factors associated with repeat infection, treatment failure and reinfection were investigated. In total, 227 MSM were included - 64 with repeat infections [28·2%, 95% confidence interval (CI) 22·4-34·5]. Repeat positivity was associated with increased pre-treatment organism load [odds ratio (OR) 1·7, 95% CI 1·4-2·2]. Of 64 repeat infections, 29 (12·8%, 95% CI 8·7-17·8) were treatment failures and 35 (15·4%, 95% CI 11·0-20·8) were reinfections, 11 (17·2%, 95% CI 8·9-28·7) of which were definite reinfections. Treatment failure and reinfection were both associated with increased load (OR 2·0, 95% CI 1·4-2·7 and 1·6, 95% CI 1·2-2·2, respectively). The most prevalent genovars were G, D and J. Treatment efficacy for 1 g azithromycin was 83·6% (95% CI 77·2-88·8). Repeat positivity was associated with high pre-treatment organism load. Randomized controlled trials are urgently needed to evaluate azithromycin's efficacy and whether extended doses can overcome rectal infections with high organism load.
authors.affiliation: Melbourne School of Population and Global Health,University of Melbourne,Victoria,Australia.
authors.forename: F Y S
authors.initials: FY
authors.lastname: Kong
authors.affiliation: Department of Obstetrics and Gynaecology,University of Melbourne,Victoria,Australia.
authors.forename: S N
authors.initials: SN
authors.lastname: Tabrizi
authors.affiliation: Melbourne Sexual Health Centre,Alfred Health and Central Clinical School,Monash University,Victoria,Australia.
authors.forename: C K
authors.initials: CK
authors.lastname: Fairley
authors.affiliation: Royal Women's Hospital and Murdoch Children's Research Institute.
authors.forename: S
authors.initials: S
authors.lastname: Phillips
authors.affiliation: Melbourne Sexual Health Centre,Alfred Health and Central Clinical School,Monash University,Victoria,Australia.
authors.forename: G
authors.initials: G
authors.lastname: Fehler
authors.affiliation: Kirby Institute,University of New South Wales,Sydney,Australia.
authors.forename: M
authors.initials: M
authors.lastname: Law
authors.affiliation: Melbourne School of Population and Global Health,University of Melbourne,Victoria,Australia.
authors.forename: L A
authors.initials: LA
authors.lastname: Vodstrcil
authors.affiliation: Melbourne School of Population and Global Health,University of Melbourne,Victoria,Australia.
authors.forename: M
authors.initials: M
authors.lastname: Chen
authors.affiliation: Melbourne School of Population and Global Health,University of Melbourne,Victoria,Australia.
authors.forename: C S
authors.initials: CS
authors.lastname: Bradshaw
authors.affiliation: Melbourne School of Population and Global Health,University of Melbourne,Victoria,Australia.
authors.forename: J S
authors.initials: JS
authors.lastname: Hocking
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D017963:Azithromycin / Q000627:therapeutic use*; D058491:Bacterial Load; D002690:Chlamydia Infections / Q000188:drug therapy* / Q000453:epidemiology* / Q000382:microbiology; D002692:Chlamydia trachomatis / Q000235:genetics / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012002:Rectal Diseases / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology; D012007:Rectum / Q000382:microbiology; D012189:Retrospective Studies; D012306:Risk; D000072339:Sexual and Gender Minorities; D014739:Victoria / Q000453:epidemiology; D055815:Young Adult
chemical_list: D000900:Anti-Bacterial Agents; D017963:Azithromycin
keywords: Chlamydia trachomatis; genovar; organism load; rectal; repeat infection