Gonorrhea
Gonorrhea, caused by Neisseria gonorrhoeae, is the second most frequently reported communicable disease in the United States: 324,901 cases were reported to CDC in 1997. N. gonorrhoeae causes uncomplicated infections of mucosal membranes including the cervix, rectum, and throat. If untreated, gonorrhea remains a major cause of pelvic inflammatory disease (PID), tubal infertility, ectopic pregnancy, and chronic pelvic pain. Epidemiologic studies provide strong evidence that gonococcal
infections facilitate HIV transmission. It is estimated that only one-half of the actual number of infections are reported.
Antimicrobial resistance in N. gonorrhoeae remains the most important challenge to controlling gonorrhea; gonococcal strains may be resistant to penicillins, tetracyclines, spectinomycin. Recently, resistance to the fluoroquinolones (ciprofloxacin and ofloxacin) has emerged. Resistance to CDC-recommended doses of ciprofloxacin and ofloxacin exceeds 10% in Hong Kong and Japan; more than 60% of isolates in some parts of the Republic of the Philippines are resistant to ciprofloxacin and ofloxacin. Currently, broad-spectrum cephalosporins are the only antimicrobial agents to which N. gonorrhoeae has not developed resistance. Surveillance for antimicrobial resistance in N. gonorrhoeae in the United States is conducted through the Gonococcal Isolate Surveillance Project (GISP); annual reports for GISP are available electronically at the above link.
The Neisseria Reference Laboratory in provides reference services to state public health laboratories. Services include reference testing for antimicrobial resistance in gonococcal isolates and confirmation of the accurate identification of Neisseria gonorrhoeae and related species. These documents include color images of Neisseria and related species to aid in the accurate identification of these species.
Chlamydial Infections.
CDC estimates that 3-5 million cases of genital chlamydial infections occur among U.S. adults each year. The economic burden of sexually transmitted chlamydial infections and related sequelae including PID, ectopic pregnancies, and tubal infertility exceeds $3.5 billion annually. Infections range from female lower genital tract infection and PID in women to urethritis, proctitis, and epididymitis in men, and to neonatal inclusion conjunctivitis and pneumonitis syndromes.
The diagnosis of genital chlamydial infections is difficult and traditionally has been based on isolation of the organism in tissue cell culture. Due to the expense and technical expertise required for cell culture, newer nonculture methods have been developed and are commercially available. Rapid, nonculture monoclonal antibody-based tests, enzyme immunoassays, nucleic acid probe tests, and, recently, nucleic acid amplification tests have been developed to detect C. trachomatis in cervical or urethral specimens and in urine; these tests are gaining widespread acceptance for the laboratory diagnosis of chlamydial infections. Patient-collected vaginal swabs have also shown promising results as alternative specimens that do not require a pelvic exam for collection. In addition, recent reports that some C. trachomatis isolates exhibit heterotypic resistance to multiple antibiotics including tetracycline emphasize the need to monitor the susceptibilities of clinical isolates to recommended therapeutic agents and to assess the suitability of newer agents for the treatment of chlamydial infections.
Syphilis
The most accurate way to diagnose any infectious disease is by growing the organism in the laboratory using material taken from patients. Attempts to grow T. pallidum have not been very successful and we rely, instead, on visualizing the organism in secretions or tissue, or serology (blood tests), to diagnose syphilis. Unfortunately, neither of these methods is ideal and proper interpretation of results is needed.
The most accurate means of diagnosing syphilis is by visualizing the organism, and there are several ways to do this. The most frequently used method for the ulcers of primary and secondary syphilis is by dark field microscopy. This requires a microscope with a special condenser. Alternatively, ulcer smears can be air dried and then examined using a fluorescent-labeled monoclonal antibody (direct fluorescent antibody or DFA) to visualize any treponemes present. This method can also be used for tissues or fluids such as amniotic fluid. Polymerase chain reaction (PCR) can detect the DNA of treponemes that are present in numbers that are too few to be see by microscropy. PCR works well for ulcers, amniotic fluid, and whole blood.
Serologic tests for syphilis have existed since the early 1900s. Today's tests are more sensitive and specific than the early tests. Syphilis in adults is diagnosed by demonstration of T. pallidum, either by dark-field or DFA, in the lesion, clinical symptoms, and/or reactive serology. If a patient is successfully treated, the titer of the nontreponemal test will fall, usually within the 6 months following treatment. If a person is reinfected, the titer will increase by a least two dilutions (e.g., from 1:4 to 1:16). Neurosyphilis is a little more problematic. A reactive VDRL test on the cerebrospinal fluid is indicative of syphilis. However, the test is not always reactive in persons who are asymptomatic. Congenital syphilis can be diagnosed based on reactive IgM tests, demonstration of the treponeme in the infants tissues or the amniotic fluid, and/or by clinical symptoms in a child born to a mother with reactive syphilis serology.
The other pathogenic treponemes that cause pinta, yaws, and endemic syphilis, can be diagnosed by clinical history and low titers in the nontreponemal tests for syphilis in adults. The diseases caused by the other pathogenic treponemes are transmitted by contact with skin lesions, and the diseases usually occur in childhood. Unlike syphilis, none of them are sexually transmitted diseases
Activities in the Syphilis Diagnostic Immunology Activity are focused on developing methods to increase the sensitivity and specificity of existing tests and to evaluate the newer tests for the diagnosis of incubating syphilis, congenital syphilis, and neurosyphilis. However, until newer tests are proven to be useful for the diagnosis of syphilis, efforts focus on ensuring that standardized tests and reagents are appropriately used so that patients are properly diagnosed and determining if novel applications of the standard tests may resolve some diagnostic problem in medically under-served patient populations. The Syphilis Diagnostic Immunology Activity in a WHO Collaborating Center for Research and Reference in Syphilis Serology and extends these functions worldwide and includes the additional responsibility to provide proficiency testing to international reference laboratories.
Chancroid.
Chancroid, caused by Haemophilus ducreyi, is one of the genital ulcerative STDs; others include syphilis and herpes simplex virus (HSV). Chancroid is prevalent in Africa and parts of Asia and has been shown to be a risk factor in the transmission of HIV. It is likely that chancroid is underreported in the United States because laboratory diagnosis of chancroid is difficult and most laboratories are incapable of culturing H. ducreyi. H. ducreyi may be identified in a gram-stained smear based on cell morphology, staining, and arrangement or by isolating and identifying the organism by its biochemical reaction patterns. Neither method of identification is very sensitive. Thus, improved methods for the identification of H. ducreyi in specimens has become a priority.
Antimicrobial resistance has emerged in H. ducreyi. The detection of high-level tetracycline resistance due to the acquisition of the TetM determinant by H. ducreyi as well as plasmids encoding resistance to beta-lactams, aminoglycosides, and other antimicrobial agents has renewed interest in the antimicrobial susceptibilities of this organism.
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