Early diagnosis of neonatal syphilis. Evaluation of a gamma M-fluorescent treponemal antibody test

Laboratory diagnosis and interpretation of tests for syphilis

The lack of a method for demonstrating the presence of Treponema pallidum by growth necessitates the use of alternative methods. Traditionally, these methods are divided into direct detection methods (animal inoculation, dark-field microscopy, etc.) and serologic tests for the presence of patient antibody against T. pallidum. Serologic methods are further divided into two classes. One class, the nontreponemal tests, detects antibodies to lipoidal antigens present in either the host or T. pallidum; examples are the Venereal Disease Research Laboratory and rapid plasma reagin and tests. Reactivity in these tests generally indicates host tissue damage that may not be specific for syphilis. Because these tests are easy and inexpensive to perform, they are commonly used for screening, and with proper clinical signs they are suggestive of syphilis. The other class of test, the treponemal tests, uses specific treponemal antigens. Confirmation of infection requires a reactive treponemal test. Examples of the treponemal tests are the microhemagglutination assay for antibodies to T. pallidum and the fluorescent treponemal antibody absorption test. These tests are more expensive and complicated to perform than the nontreponemal tests. On the horizon are a number of direct antigen, enzyme-linked immunosorbent assay, and PCR techniques. Several of these techniques have shown promise in clinical trials for the diagnosis of congenital syphilis and neurosyphilis that are presently difficult to diagnose.

Enzyme-linked immunosorbent assays for detection of immunoglobulin M to nontreponemal and treponemal antigens for the diagnosis of congenital syphilis

Sera from newborn infants born of mothers with a high risk of syphilis were examined for immunoglobulin M (IgM) antibodies in two different enzyme-linked immunosorbent assays (ELISAs), using either purified flagella from Treponema phagedenis biotype Reiter or the Venereal Disease Research Laboratory (VDRL) antigen as the antigen. All sera were also examined by the fluorescent treponemal antibody absorption (FTA-ABS) test for IgM. Three different groups of patients were studied. Group 1 consisted of 84 women and their newborn infants from a high-risk population for syphilis. Congenital syphilis was diagnosed in one child who had an IgM-positive cord blood specimen in both the ELISA and the FTA-ABS test. Group 2 consisted of 10 mothers and their newborn children. All mothers had positive syphilis-screening tests, and all children had signs of congenital syphilis. All but one child had positive IgM tests. Group 3 consisted of 15 mothers and their newborn children. These mothers had been treated for syphilis late in pregnancy, and all had a positive screening test at delivery. Two of the children had positive IgM tests, probably caused by reactivity after late intrauterine treatment of congenital syphilis. The specificities of the IgM tests were high when evaluated with sera from newborn children without signs of congenital syphilis. Even though IgM rheumatoid factor was found in all of the children tested with definite congenital syphilis, the rheumatoid factor did not cause false-positive results in either the VDRL ELISA or the flagellum ELISA. No significant IgG-IgM competition was noticed in the ELISAs. This study also confirmed that IgA antibodies do not cross the placenta; most newborn children with congenital syphilis were positive in the VDRL ELISA for IgA. Both the VDRL ELISA and the flagellum ELISA are very useful in the diagnosis of congenital syphilis and may be substitute for the FTA-ABS test. The VDRL ELISA for IgM will be especially useful in developing countries with a high incidence of congenital syphilis.

Early congenital syphilis still occurs

Seven cases of early congenital syphilis have been recorded in the past 10 years in the Mersey Regional Health Authority. Antenatal serology was initially negative in five mothers, who were either incubating or acquired the infection later, and treatment had probably failed in two women given erythromycin for syphilis during pregnancy. Serology should be repeated later in pregnancy in those at high risk. Social factors that define this group include women who book for antenatal care late in pregnancy, have a past history of sexually transmitted disease, and have multiple consorts. Clinical signs in the infant such as failure to thrive, hepatosplenomegaly, symmetrical rash, rhinitis, and osteochondritis should alert the clinician to the possibility of congenital syphilis. Adequate management of mother and baby requires close liaison between the genitourinary physician, microbiologist, obstetrician, and paediatrician. Penicillin remains the treatment of choice.

Survival of treponemes after treatment: comments, clinical conclusions, and recommendations

Treponemes may persist after treatment that has been accepted as effective; the reasons for this are discussed. Nevertheless, the epidemic of syphilis after the second world war was not followed by an epidemic of late syphilis, and the results of treatment with penicillin are excellent. Neurological signs may progress in some treated patients, and the standard doses of soluble penicillin and any dose of benzathine penicillin (even with added probenecid by mouth) cannot be relied on to achieve treponemicidal concentrations in the cerebrospinal fluid (CSF). There are no large scale studies of CSF findings after treatment of early syphilis with benzathine penicillin. Standard dosage, such as procaine penicillin G 600 000 international units (IU) by intramuscular injection for 10 days, is the treatment of choice for the patient suffering from uncomplicated early syphilis; this should be preferred to benzathine penicillin, which should only be used when standard treatment as above cannot be given. Treponemicidal concentrations of penicillin should be achieved in the CSF of patients suffering from neurosyphilis by schedules of probenecid by mouth and procaine penicillin by single daily intramuscular injections; treatment should last for 17 to 21 days. Benzathine penicillin should not be used for the treatment of patients suffering from neurosyphilis or from the iritis of late syphilis including that accompanying interstitial keratitis. Treatment for interstitial keratitis should initially be as for neurosyphilis, but in recurrent cases it may have to be prolonged to eradicate Treponema pallidum that is dividing slowly. Doxycycline 200 mg by mouth daily for 21 days provides a supervisable outpatient schedule for patients allergic to penicillin. Cephaloridine (and probably cefuroxime and the new cephalosporins) may be useful for patients who are allergic to penicillin but have not developed anaphylactic allergy. If erythromycin is used for treating syphilis in pregnant women who are allergic to penicillin, then the newborn babies should be treated with penicillin.

A reappraisal of the value of the IgM fluorescent treponemal antibody absorption test in the diagnosis of congenital syphilis

To re-evaluate the usefulness of the IgM fluorescent treponemal antibody absorption test in the diagnosis of congenital syphilis, three groups of infants were investigated. Group 1 infants showed that the test was always negative in normal neonates born to seronegative mothers. From Group 2 infants we determined the standardization of the test using commercially prepared conjugate to allow the maximum exclusion of false positive and negative results. Studies on Group 3 neonates confirmed that the standardized test was extremely successful in determining whether or not an asymptomatic infant was infected with Treponema pallidum. Finally it was shown that the standardization of the test varies with different commercially prepared conjugates. From the investigation it was concluded that the IgM FTA test, if suitably standardized, was a highly successful method for diagnosing congenital syphilis, especially in asymptomatic neonates.