A 22-year-old man sees a physician because of a purulent discharge from his penis. The diagnosis of gonorrhea is made (and later confirmed by a lab) and he is given a single dose of ceftriaxone (a cephalosporin) by intramuscular injection. He improves initially but, after a few days, he notices a milder but persistent urethral discharge and dysuria. He is worried that he might not have been cured, so he comes to see you for a second opinion. He tells you that he has not had sexual intercourse since his visit to the original physician. He also brings his latest sexual partner, a 20-year-old woman, with him, even though she does not have any pain or vaginal irritation. On physical examination, the patient has a small amount of clear urethral discharge and his female partner has greenish discharge emanating from the mouth of her cervix. Her cervix is inflamed and bleeds easily when a swab is used to remove adherent secretions. Gram stains from both patients reveal numerous neutrophils, but no evidence of Gram-negative diplococci.

Question 4.1: What is your preliminary diagnosis of the male patient's condition and what test(s) would you order to confirm it?

The absence of Gram-negative diplococci in the male's urethral smear argues against a relapse of the original gonococcal infection (which might occur if the strain were resistant to the antibiotic that was used for treatment). Any sort of re-infection since he saw the original physician is very unlikely, assuming that he is telling the truth about not having intercourse since then. The fact that his present urethral discharge is milder than the previous one and is clear instead of mucoid suggests a nongonococcal urethritis (NGU), although NGU and gonococcal urethritis are often indistinguishable on clinical grounds alone. If the patient has NGU, then he was most likely co-infected with gonorrhea and NGU at the time of his original visit to a physician. A lab test for Chlamydia trachomatis, the most frequent cause of NGU, would be appropriate in this case.

Question 4.2: Was the original physician's treatment of the male patient appropriate?

The original physician failed to follow the current recommendations of the U.S. Public Health Service for treating gonorrhea. Those recommendations take into account the fact that roughly 45% of gonorrhea cases in the U.S. involve co-infection with chlamydial species (NGU). As a result, treatment for the gonococcus should always be followed by a treatment regime that is effective against Chlamydia spp. (For details, see answer to question 2.6 in case 2, above.)

Question 4.3: What are possible causative agents of this disease?

Chlamydia species (mostly C. trachomatis, but also C. psittaci) are believed to cause 20-50% of all cases of NGU. Other possibilities include Ureaplasma urealyticum (a mycoplasma that may cause 15-30% of the cases), Trichomonas vaginalis (a protozoan), and herpes simplex virus. In as many as 20% of NGU cases in the U.S., the causative agent is not identified.

Question 4.4: What type of sample should be taken to confirm your diagnosis and how should it be collected?

The type of specimen collected depends on the analytical method used by the lab. There are four types of procedures available to confirm C. trachomatis infection: (1) direct microscopic examination of tissue scrapings for typical intracytoplasmic inclusions or elementary bodies, (2) isolation of the organism in cell culture, (3) detection of chlamydial antigens or nucleic acid by immunologic or hybridization methods, and (4) detection of antibody in serum or local secretions.

Direct microscopic examination of Giemsa-stained cell scrapings has an unacceptably low level of sensitivity, and false-positive interpretations by inexperienced observers are common. Cell culture techniques for C. trachomatis are available in most large medical centers, but not in other clinical settings. They are also quite expensive, so various non-culture-dependent alternatives have been developed. For the direct immunofluorescent antibody (DFA) test, genital secretions are smeared on a slide and stained with fluorescein-conjugated antibody specific for chlamydial antigens.

Recent reports indicate that culture is not more sensitive than DFA, ELISA, or DNA probe tests when an expanded definition of a true positive test is used:

€ Positive culture, or

€ Positive non-culture test confirmed by: 1) a second nonculture test, or 2) a blocking antibody or probe competition assay.

Using this expanded definition, most recent reports indicate that DFA/ELISA/ DNA probe methods are 70-93% sensitive and 95-98% specific. However, in low prevalence populations, even a specificity of 97-98% can result in a substantial number of false positive tests. Recognizing this problem, the CDC recommends that each nonculture test with a positive result should be confirmed with a second test as per the definitions above. The DFA test performed on a slide smear has the advantage of a short turnaround time (within minutes of receipt in the laboratory) and the ability to assess specimen quality, but has the requirement of an FA scope and trained personnel. Disadvantages include lower sensitivity in males (particularly in low prevalence populations), the inability to confirm with a second test if the laboratory receives only a slide, and difficulty in processing a large number of specimens. However, false positive results can be minimized with the use of experienced personnel and rigorous quality control procedures. False positive chlamydia ELISA antigen detection results may occur as well, particularly with swab specimens from non-genital sites (e.g., rectal, eye, respiratory). Second test confirmation of positives should be done. With ELISA performed on specimens received in universal transport media, either a DFA or a blocking antibody with a repeat ELISA can be used for confirmation. The DFA can be done on the same day, while the repeat ELISA must usually wait for the next day.

Urine specimens for nucleic acid-based tests should be "first catch" samples of the first 30 ml of urine produced (to maximize the chance that chlamydia will be present). Because C. trachomatis is an intracellular pathogen, adequate specimens for other analytical techniques must include epithelial cells. The optimal procedure is an endourethral swab taken from an area 2 to 4 cm inside the urethra. If the specimen is being taken for culture, a Dacron-tipped swab should be utilized; calcium alginate or cotton swabs should be avoided. For culture, the specimen must be placed immediately into transport medium and then either refrigerated (if it will get to lab within 12-18 hrs) or forzen at -70C (when longer storage is anticipated). Neither refrigeration nor rapid transport is needed for non-culture-based diagnostic methods (a major advantage of those methods).

Question 4.5: What is the prevalence of this disease? In what groups is it seen most often?

C. trachomatis genital infections are the most frequently seen bacterial STD in the U.S., with an estimated 4 million cases occurring each year. The number of cases in the U.S. is rising steadily, probably because of increased testing and reporting. Estimated comprehensive cost of diagnosis and treatment in the U.S. is $2.8 billion.

As with many STDs, the age of peak incidence for genital C. trachomatis infections is the late teens and early twenties. The prevalence among young men is at least 3-5% for those seen in general medical settings or urban high schools, >10% for asymptomatic soldiers undergoing routine examinations, and 15-20% for heterosexual men seen in STD clinics. Prevalence varies widely with the geographic locale. The ratio of chlamydial to gonococcal urethritis is highest for heterosexual men and for those of high socioeconomic status and is lowest for homosexual men and indigent populations. The prevalence of cervical infection among women is about 5% for asymptomatic college students and prenatal patients, >10% for women seen in family planning clinics, and >20% for women seen in STD clinics. As in men, prevalence varies substantially by geographic locale.