Recommendations as for treatment of chlamydia infection by Doxycycline or Azithromycin

Similar to N gonorrhoeae, Chlamydia trachomatis causes infections of the pharynx, urethra, and rectum in MSM. Chlamydia is better recognized as an asymptomatic or minimally symptomatic infection. Recent data on rectal chlamydial infections in MSM show increases over the past 5 years and a 10% prevalence of asymptomatic infection. Additionally, studies in MSM show that chlamydia may cause up to 20% of cases of nongonococcal urethritis (NGU), similar to the proportion of NGU attributable to chlamydia in heterosexual men. In asymptomatic populations of MSM undergoing urine screening for urethral chlamydial infection at anonymous HIV testing sites, 0.5% had chlamydial infection in Denver and 3% in San Francisco. Data on pharyngeal chlamydia suggest the prevalence is low, ranging from 0.5% to 2%.

Before the advent of NAAT for the diagnosis of rectal chlamydial infection, the role of chlamydia in proctitis was underappreciated. One study using NAAT showed that 12% of MSM with clinical proctitis who attended an STD clinic had chlamydial infection. Another recent study demonstrated that 20% of MSM with rectal symptoms were infected with C trachomatis. Comparison of NAAT versus culture identified six rectal specimens positive for chlamydia by NAAT and none by culture in that study. In a research cohort of MSM, 4.2% had rectal chlamydia using the polymerase chain reaction (PCR) assay, while only 0.5% of this population had urethral chlamydia. Another study in Seattle compared different methods of processing rectal specimens for the PCR assay and found no differences by the means of specimen processing. Other verification studies in individual laboratories have confirmed the adequate performance of NAATs for the detection of rectal chlamydial infection.

To date antimicrobial resistance has not been a significant problem in the management of chlamydial infections. One reported case in 2000 documented C trachomatis resistant to azithromycin (generic zithromax) and doxycycline, but the extent of resistance at the population level appears limited. Routine surveillance for decreased antimicrobial susceptibility of C trachomatis is not performed, however, and monitoring relies on case reports. Because isolation of C trachomatis depends on tissue culture systems that are less sensitive than NAAT, defining antimicrobial susceptibility is largely dependent on independent research laboratories and has not been a public health priority.

The recommended treatment of uncomplicated chlamydial infection is doxycycline (Adoxa, Doryx, Monodox, Periostat, Vibra-tab, Vibramycin), 100 mg orally twice daily for 7 days, or azithromycin (generic Zithromax, Zmax), 1 g orally as a single dose. Doxycycline is significantly less expensive than azithromycin, is equally efficacious, and offers the patient a continuous reminder to abstain from sexual activity until treatment is completed. In addition, doxycycline is effective against incubating syphilis. Azithromycin can be given under directly observed therapy to assure adherence, and because of its excellent safety profile is easily amenable to being provided to patients to give to their recent sex partners, either through prescription or by directly providing additional doses. Azithromycin, however, is not recommended for the prevention or treatment of syphilis, because the prevalence of azithromycin-resistant syphilis in some areas is 80%. In an effort to augment the control of chlamydia in California, as of January 2001 state law authorized medical providers to dispense additional chlamydial therapy for partners of patients with chlamydial infection.