Diagnosis of Chlamydia Trachomatis

Chlamydia trachomatis is the most prevalent bacterial pathogen causing sexually transmitted disease (STD) in the western world. It often goes undiagnosed and may be inadequately treated when it is diagnosed. Some of the reason for this underdiagnosis is that chlamydial infections often produce no symptoms and only mild, non-specific signs. If left untreated it can persist for at least 15 months1 and can have potentially serious lifetime consequences. The main burden of morbidity falls upon women.2 Large reservoirs of the disease can be found both in asymptomatic men3 and women.4 In fact up to 25% of infected men and 50-70% of infected women are asymptomatic. Consequently, the challenge of chlamydia control remains the identification of asymptomatic individuals. How do we identify patients who may be at risk for chlamydia infection? As with most conditions we have to maintain a high index of suspicion. Certain patient populations are at higher risk.5 These include:
  • Patients with contacts with known STDs
  • Persons with a new partner in the past 2 months
  • Persons with more than 2 partners in the past 12 months
  • Individuals using non barrier methods of contraception
  • Street youth, IV drug users, commercial sex workers
  • Persons who have had sex in countries where certain STDs are epidemic
  • Homosexual men
Once a patient has been identified as being at high risk, the question of diagnosis arises. There are problems, however, with the present methods of testing. Currently we usually do cervical swabs, but to be accurate endocervical epithelial cells must be included on the swab as C. trachomatis is an obligate intracellular parasite. Unfortunately many swabs include only mucus. Indeed, one study estimated that 10-35% of endocervical specimens were inadequate.6 Newer DNA amplification tests (polymerase chain reaction PCR and ligase chain reaction LCR) that can be used to test urine as well as cervical swabs are becoming available. The overall sensitivities of amplified DNA tests are in the range of 90-95%, compared to a sensitivity of only 60-65% for culture. There are a few tips that will increase the effectiveness of intraurethral swabs. These include:
  • Warning the patient that there will be some discomfort
  • Use a thin swab with a flexible wire shaft
  • Ideally the patient will not have voided for 2 hours, as voiding reduces the anount of exudate and may decrease the ability to detect organisms
  • Moisten the swab with water before insertion to reduce discomfort
  • Introduce the swab slowly (3-4 cm in males and 1-2 cm in females), rotate slowly and withdraw gently
  • Directly inoculate the culture medium or place the swab in the transport medium.
For collection of a cervical specimen:
  • View the cervix and remove any overlying mucous and vaginal secretions
  • Insert a sterile cotton tip swab 1-2 cm into the endocervical canal and rotate
  • Rotate for 10-30 seconds and withdraw
  • Directly inoculate the culture medium or place in the transport medium

The question of generalized screening remains controversial. Although there are some studies that suggest that, in some patient populations screening all women under 30 is cost effective7,8 for most regions this is not practical. Two groups that should be screened are pregnant women and donors of semen.

This article discusses chlamydia only, but for practical purposes, if you are testing for chlamydia, you should probably look for gonorrhea as well.

Treatment of this disease at the early stage is simple and effective using Doxycycline 100 mg orally twice daily for seven days, Erythromycin 500 mg four times daily for seven days, or Azithromycin 1 gram as a single witnessed dose (probably better for compliance). Don't forget that patients and contacts should refrain from unprotected intercourse until the treatment course is completed - 7 days for single dose treatment. Failure to treat may lead to such consequences as infertility, ectopic pregnancy and chronic pelvic pain.

- John Hickey

Thanks to Dr. Kevin Forward, Service Chief, Division of Microbiology, Dalhousie University, Halifax for reviewing the draft copy of this article.

References:
  1. McCormack WM, Alpert S, McComb DE, Nichols RI, Semine DZ, Zinner SH. Fifteen-month follow-up study of women infected with Chlamydia trachomatis. N Engl J Med 1979; 300: 123-125.
     
  2. Thompson SE, Washington AE. Epidemiology of sexually transmitted Chlamydia trachomatis infections. Epidemiol Rev 1983; 5: 96-123.
     
  3. Harry TC, Saravanamuttu KM, Rashid S, Shrestha TL. Audit evaluating the value of routine screening of Chlamydia trachomatis urethral infections in men. Int J STD AIDS 1994; 5: 374-375.
     
  4. Hopwood J, Mallinson H, Agnew E. Chlamydia screening - should it be offered as a routine? Br J Family Plan 1990; 16: 59-67.
     
  5. Canadian STD Guidelines 1998
     
  6. Larson J, Wulf H, Friis-Moller A. Comparison of a fluorescent monoclonal antibody assay and a tissue culture assay for routine detection of infections caused by Chlamydia trachomatis. Eur J Clin Microbiol 1986; 5:554-558.
     
  7. Scholes D, Stergaghis A, Heidrich F et al. Prevention of pelvic inflammatory disease by screening for cervical chlamydial infection. N Engl J Med 1996; 334: 1362Ñ1366.
     
  8. MR Howell, TC Quinn, CA Gaydos. Screening for Chlamydia trachomatis in asymptomatic women attending family planning clinics. Annals of Internal Medicine 1998 128:277-84.

You can search for abstracts of the above references by following this link: PubMed

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