LabMed

Male and Female Reproductive, Infectious Diseases (Sexually Transmitted Diseases; STDs)

At a Glance

Lesions of the genital skin and mucous membranes most commonly result from sexually transmitted diseases (STDs). Infectious diseases covered in this chapter include syphilis, herpes simplex virus (HSV), chancroid, lymphogranuloma venereum (LGV), human papillomavirus infection (HPV), and Chlamydia/gonorrhea.

Syphilis is a sexually transmitted disease caused by the spirochete Treponema pallidum. The disease manifests in many different organ systems, but the genitalia are affected in primary and secondary syphilis. Chancres of primary syphilis are typically solitary ulcers with clean, indurated margins. Nodules or plaques (also referred to as condyloma lata) of secondary syphilis occur in warm, moist areas of the body. Condyloma lata are teeming with spirochetes and extremely infectious.

Primary genital HSV infection can range from asymptomatic infection to a severe syndrome with multiple painful genital ulcers, fevers, dysuria, and tender lymphadenopathy. Recurrences usually present with fewer genital lesions and systemic symptoms than primary infection. Recurrences are more common in immunocompromised patients, who also suffer from more severe symptoms.

Chancroid ulcers have ragged and undermined borders with less induration than syphilitic ulcers; hence, the name “soft chancre.”

LGV is a genital ulcer disease caused by Chlamydia trachomatis serovars L1, L2, or L3. Outbreaks have been reported since 2003 in North America and Europe. LGV begins as a small papule or ulcer, but presents 2-6 weeks later with inguinal or femoral lymphadenopathy, often with systemic symptoms.

HPV causes anogenital lesions ranging in appearance from flat plaques to large verrucous masses.

Dysuria in men may be a presenting symptom of urethritis, prostatitis, epididymitis, or urinary tract infection. Gonorrhea is a common cause of urethritis in the United States. Up to 30% of men with gonococcal urethritis also have Chlamydia infection. A purulent urethral discharge is more often seen with gonorrhea than with Chlamydia.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

Microscopic examination of syphilitic lesions under the light microscope is not useful, as Treponema pallidum is extremely thin and does not stain with the Gram stain. Although darkfield microscopy may be diagnostic, clinics and hospitals rarely have darkfield microscopes any longer. T. pallidum also cannot be cultured in the laboratory. Direct fluorescent antibody testing for T. pallidum (DFA-TP) is an alternative method for diagnosis of syphilis, but it is not routinely performed in most STD clinics. Serologic testing is the mainstay of diagnosis. The classic syphilis screening test is detection of serum antibodies to non-treponemal antigens (i.e., rapid plasma reagin [RPR] test or the Venereal Disease Research Laboratory [VDRL] test).

If the screening test is positive, a confirmatory test is performed, which detects serum antibody to treponemal antigens (i.e., fluorescent treponemal antibody absorption [FTA-ABS], T. pallidum particle agglutination assay [TP-PA], microhemagglutination test for antibodies to T. pallidum [MHA-TP], and T. pallidum enzyme immunoassay [TP-EIA]). In secondary syphilis, the non-treponemal test may rarely be falsely negative because of the prozone effect. The non-treponemal test usually reaches its highest titer in secondary syphilis and declines in titer with latency or treatment. Non-treponemal tests are semi-quantitative and are reported as titers, whereas treponemal tests are qualitative.

TP-EIA has recently become the favored method of confirmatory testing in many laboratories because of its ease of use as an automated assay. Some laboratories have implemented a nontraditional syphilis screening approach in which the TP-EIA is the screening test and the non-treponemal test is confirmatory. This testing approach has been adopted in some areas because of financial reasons, as the EIA format is cheaper and easier for high-volume laboratories. If the non-treponemal test is positive in the nontraditional algorithm, the patient is considered positive for syphilis. However, the significance of a positive TP-EIA without confirmation by a non-treponemal test is unknown.

HSV may be diagnosed by culture, polymerase chain reaction (PCR), direct fluorescent antibody (DFA), Tzanck smear, or serology. PCR has emerged as an accurate and rapid method of diagnosis of HSV in clinical specimens. However, PCR has not been widely adapted by clinical laboratories because of the cost and expertise required in running the test. Thus, culture is still considered a standard diagnostic method for some specimen types. HSV grows quickly within conventional culture tubes (2-3 days). Some laboratories have adopted more rapid culture techniques with shorter turn-around-times, some of which generate results within 24 hours.

Immunofluorescence by DFA can be performed on lesional scrapings from active genital lesions. The DFA is a specific test, and results are available within a few hours. The Tzanck smear can also be performed on lesional scrapings. Multinucleated giant cells with or without inclusions are diagnostic on the stained Tzanck smear, but the method has poor sensitivity and specificity. HSV-1 and HSV-2 may be differentiated in the laboratory by several of the methods mentioned. Serologic tests for herpes antibodies are available and can distinguish between HSV-1 and HSV-2, but the utility of serologic testing has been debated.

Most laboratories do not have the specialized media needed for growth of Haemophilus ducreyi, the causative agent of chancroid. No Food and Drug Administration (FDA)-approved molecular test for chancroid exists in the United States. Thus, the diagnosis is largely clinical.

Diagnosis of LGV is difficult, as laboratory testing is not well standardized. Molecular nucleic acid amplification techniques (NAAT) are not currently approved by the FDA, but research suggests that molecular testing is highly sensitive and specific. Serologic tests are currently the most common means of diagnosing LGV.

HPV does not grow in cell culture and must be diagnosed by cytologic or molecular means. Cytologic assessment of the cervical or anal Papanicolaou (Pap) smear for koilocytes and nuclear atypia is routinely employed. However, cytology is best used as a diagnostic method in conjunction with molecular testing. Nucleic acid amplification (NAAT) assays are the most commonly used molecular-based diagnostic methods and are highly sensitive and specific.

Sexually active men with dysuria should be evaluated for urethritis. Urethral swabs may be collected, particularly if a urethral discharge is present. The specimen should be collected on a calcium alginate swab. Cotton swabs should be avoided, as they are toxic to Neisseria gonorrhoeae. A swab containing material from the urethra should be gently rolled across a clean microscope slide. Rough rubbing or streaking on the slide may disrupt the cellular morphology, leading to difficulty in assessing intracellular or extracellular location of organisms. The smear should be air-dried.

In the laboratory, the smear is assessed for polymorphonuclear neutrophils and the typical intracellular gram-negative diplococci. Extracellular gram-negative diplococci are not diagnostic of N. gonorrhoeae in men. Nongonococcal urethritis due to Chlamydia trachomatis cannot be diagnosed by a Gram stain smear of urethral exudate. NAAT testing of urine (male or female) or male urethral specimen is the preferred method of diagnosis of urethritis. Although Chlamydia can be grown in culture, NAAT testing is more sensitive. The sensitivity of N.gonorrhoeae culture is relatively poor, as the organism is fastidious and does not survive easily outside of the body.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

Urethral Gram stains should not be performed on women for the diagnosis of gonorrhea, as normal flora of the female genital tract may stain as gram-negative diplococci, potentially leading to a false-positive diagnosis of gonorrhea.

If the patient has previously taken antibiotics, N. gonorrhoeae may not grow in culture because of its fastidious nature. Conversely, antibiotic usage does not affect NAAT results as profoundly.

What Lab Results Are Absolutely Confirmatory?

Identification of T. pallidum by darkfield microscopy or by DFA-TP is confirmatory for syphilis. For most of the testing previously discussed, molecular or NAAT results are confirmatory.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

The prozone phenomenon in syphilis testing is associated with false-negative non-treponemal tests. Prozone results from high levels of antibodies that, rather than binding to the antigens in the test kit, bind to each other. If secondary syphilis is highly suspected and the RPR or VDRL is negative, the laboratory staff can retest the sample after diluting the specimen. If prozone was present, the repeat specimen will be positive after dilution, since the antibodies are diluted and no longer bind to each other. However, the clinician must notify the laboratory of a potential prozone effect in a patient with a high clinical suspicion of syphilis and a negative screen. Patient specimens are not routinely screened for the prozone effect.

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