Advanced Techniques in Diagnostic Microbiology

354 A. C. T. Lo and K. M. Kam
in turn, lead to decrease in case burden and ultimately eliminate the reservoir of
infection.
Because of difficulties in selection of representative samples for evaluation of
commercially available test kits, interpretation of test performance (specificity,
sensitivity) must be done with clear definition of the prevalence of disease in the
test population. Also, because of obvious social stigma that can be associated
with various STDs, accuracy (positive predictive values) of tests should be of
highest priority in selection of those that are appropriate for the patient. Presence
of nonviable gene fragments can, in principle, generate positive signals in all the
molecular tests. This means that vigorous evaluation and correlation studies must
be done before the significance of their presence can be adequately interpreted.
Although rapid tests do significantly reduce turn-around time and this will expectedly
generate pressures from both clinician and patient, the choice of molecular
tests should not depend on this consideration alone. In less well developed countries,
cost implications of some molecular tests can become an insurmountable one
that must be balanced with available resources. However, with rapid evolution and
refinement of different test platforms, it is to be expected that unit prices of many
molecular tests will decline significantly in the very near future.
This paper intends to review the currently developed and available molecular
diagnostics of common STDs including (1) Neisseria gonorrhoeae; (2) Chlamydia
trachomatis; (3) Treponema pallidum; (4) Haemophilus ducreyi; (5) Mycoplasma
and Ureaplasma; (6) Trichomonas vaginalis; (7) herpes simplex virus; and (8)
human papilloma virus.
Neisseria gonorrhoeae
Neisseria gonorrhoeae is the etiological agent of gonorrhea and remains a major
sexually transmitted infection worldwide. In the United Kingdom, the number of
gonorrhea cases has been rising each year since 1995 (more than 60 million cases)
(Ward et al., 2000) with a 56% increase overall, including a 25% rise in 1999
(Ward et al., 2000).
Due to the extensive antigenic variability of many gonococcal surface components,
no effective vaccine for N. gonorrhoeae is available (Unemo et al., 2003).
Geographic and international surveillance of the epidemiological characteristics
as well as the antibiotic susceptibilities of the pathogen become essential in the
prevention and control of this infection. From both local and global perspectives,
N. gonorrhoeae strains continue to evolve phenotypically and genotypically over
time. It is therefore essential to develop discriminative and precise characterization
laboratory techniques that can help control the transmission of infections,
especially those caused by antibiotic-resistant strains.
Traditional Diagnostic Methods
There are several traditional diagnostic methods for N. gonorrhoeae such as direct
stained smear examination, antigen detection, and culture. Sensitivity of direct