Serological Testing. Because of serologic cross-reactions between Mycoplasma pneumoniae and M. genitalium, there are no standardized serological tests for M. genitalium.37
Nucleic Acid Amplification Tests.M. genitalium diagnosis currently is made based exclusively on nucleic acid amplification testing (NAAT) methodology (polymerase chain reaction [PCR] or transcription-mediated amplification [TMA]), which is the only clinically useful method to detect M. genitalium. TMA for M. genitalium is commercially available in an analyte-specific reagent (ASR) format, but this has not been approved by the Food and Drug Administration (FDA).38 A study analyzing urogenital specimens from female patients via this TMA product found a 98.7% true-positive result when confirmed with repeat testing or alternative-target TMA, and only a 0.5% false-negative rate.38 There is evidence that this TMA product can be used to identify M. genitalium in urine, stool, and pharyngeal samples.39 These assays are currently available in some reference labs and large medical centers but are not widely available. Table 1 summarizes the diagnostic methods for M. genitalium.
N. gonorrhoeae
Gonococcal infection can involve the urogenital tract, but can also be extra-urogenital. The method of diagnoses of urogenital infections has expanded from Gram stain of urethral or cervical discharge and the use of selective media culture (usually Thayer-Martin media)40 to molecular methods such as NAATs, which have a higher sensitivity than cultures.41,42
Gram Stain. A Gram stain that shows polymorphonuclear leukocytes with intracellular gram-negative diplococci can be considered diagnostic for N. gonorrhoeae urethritis infection in symptomatic men when samples are obtained from the urethra.43 A retrospective study of 1148 women with gonorrhea revealed that of 1049 cases of cervical gonorrhea, only 6.4% were positive by smear alone; and of 841 cases of urethral gonorrhea, only 5.1% were positive by smear alone; therefore, other diagnostic methods are generally preferred in women.44 Because Gram stain of vaginal specimens is positive in only 50% to 60% of females, its use in women and in suspected extragenital gonococcal infections is not recommended.43-45 When Gram stain was performed in asymptomatic men, the sensitivity was around 80%.39 Thus, in asymptomatic men with a high pre-test probability of having the infection, the use of other additional testing would increase the rate of detection.43
Culture.Urethral swab specimens from males with symptomatic urethritis and cervical swab samples from females with endocervical infection must be inoculated onto both a selective medium (eg, modified Thayer-Martin medium or Martin Lewis medium) and a nonselective medium (eg, chocolate agar). A selective medium is used because it can suppress the growth of contaminating organisms, and a nonselective medium is used because some strains of N. gonorrhoeae are inhibited by the vancomycin present in the selective medium.40 Specimens collected from sterile sites, such as blood, synovial fluid, and cerebrospinal fluid, should be streaked on nonselective medium such as chocolate agar. The material used for collection is critical; the preferred swabs should have plastic or wire shafts and rayon, Dacron, or calcium alginate tips. Materials such as wooden shafts or cotton tips can be toxic to N. gonorrhoeae.40 The specimen should be inoculated immediately onto the appropriate medium and transported rapidly to the laboratory, where it should be incubated at 35º to 37ºC with 5% CO2 and examined at 24 and 48 hours post collection.40 If the specimens cannot be inoculated immediately onto the appropriate medium, the specimen swab should be delivered to the lab in a special transport system that can keep the N. gonorrhoeae viable for up to 48 hours at room temperature.46
The following specimen collection techniques are recommended by the CDC:40
In males, the cotton swab should be inserted about 2 to 3 cm into the urethral meatus and rotated 360° degrees 2 or 3 times.
In females, collection of cervical specimens requires inserting the tip of the swab 1 to 2 centimeters into the cervical os and rotating 360° 2 or 3 times.
Samples obtained outside of the urogenital tract: rectal specimens may be obtained by inserting the swab 3 to 4 cm into the rectal vault. Pharyngeal specimens are to be obtained from the posterior pharynx with a swab.
Culture tests allow the clinician to assess antimicrobial susceptibility and are relatively low cost when compared with nucleic acid detection tests. The sensitivity of culture ranges from 72% to 95% for symptomatic patients, but drops to 65% to 85% for asymptomatic patients.45-47 This low sensitivity is a major disadvantage of culture tests when compared to NAATs. Other disadvantages are the need for the specimens to be transported under conditions adequate to maintain the viability of organisms and the fact that 24 to 72 hours is required to report presumptive culture results.42 Antimicrobial sensitivity testing generally is not recommended; however, it is advisable to perform antimicrobial sensitivity in cases of treatment failure or disseminated gonococcal infection.12
