Guidelines for serological testing for syphilis

Although we may wish it were not so, syphilis, like the poor, will always be with us—at least for the foreseeable future. The levels of both are determined to a large extent, by political instability and socioeconomic deprivation. Overall, the incidence of syphilis is low in Western Europe (approximately 0.3 cases/ 100 000 in England in 1998) although it has reached epidemic proportions in the Russian Federation where the levels in 1996 exceeded 900 cases/100 000 in men and women in the 20–29 year old age group. The need to maintain eVective strategies for syphilis control, which must include diagnosis and management, in areas of low prevalence such as the United Kingdom, is reinforced by the recent local outbreak of heterosexually acquired syphilis in South West England as well as the marked increase in homosexually acquired infection in the Manchester area. A significant proportion of the infected men in Manchester were HIV positive so the overall community health gain from rapid and eVective diagnosis extends well beyond syphilis: ulcerative sexually transmitted infections promote HIV transmission by augmenting HIV infectiousness and HIV susceptibility via a variety of biological mechanisms. The importance of the serological diagnosis of syphilis has now been recognised with the publication of the excellent guidelines for serological testing for syphilis in diagnostic microbiology laboratories by the PHLS Syphilis Serology Working Group. These complement the recent national guidelines on the management of syphilis 8 and together they should improve the overall diagnosis and management of syphilis within the United Kingdom and beyond. Guidelines for serological diagnosis for syphilis are long overdue. The last guidelines which were produced by the World Health Organization in 1982 recommended the use of a cardiolipin antigen test such as the Venereal Diseases Reference Laboratory (VDRL) or rapid plasma reagin (RPR) test and the Treponema pallidum haemagglutination assay (TPHA) for screening for syphilis. The new recommendations extend the WHO guidelines by suggesting that treponemal antigen based enzyme immunoassays (EIAs) are an appropriate alternative to the combined VDRL/RPR and TPHA screen. EIA as a single screening test was shown to give similar results to the VDRL/RPR and TPHA combination some years ago and is already used by many laboratories, particularly those with large workloads. Results of the UK National External Quality Assessment Scheme for Microbiology syphilis serology distribution in April 2000 showed that 56% (130/232) of responding laboratories within the United Kingdom used an EIA (quoted with permission of the UK NEQAS organiser). Advantages of EIA include automated (or semiautomated) processing, objective reading of results, and interfacing with the laboratory computer system to allow electronic report generation. The widespread and growing use of automation and computerisation in laboratories has led to the reorganisation and rationalisation of microbial serology to meet the continuous demands for increased cost eVectiveness in service delivery. Several requests to the author for advice suggest that, owing to rationalisation of services and developments in automation and computerisation, there is a trend for syphilis testing to move from bacteriology laboratories to dedicated microbial serology laboratories that traditionally may have dealt mainly with viral serology. These changes make the guidelines particularly timely as many laboratories may be taking on syphilis testing for the first time. There is also a trend for fewer laboratories to perform confirmatory testing, preferring to forward specimens reactive on screening to a specialised laboratory or centre. The guidelines outline the current serological tests for syphilis and highlight the diVerences in screening practice between the United Kingdom and the United States. They contain an excellent algorithm for “Treponemal antibody screening and confirmatory testing” which is based on the key recommendations of the group. The guidelines recognise that there are a number of commercial tests of any given format and that these can vary in performance characteristics. Decisions on which test a laboratory uses will be based on many factors including cost, ease of use, suitability for automation, compatibility with the format of other tests already in use in the laboratory, as well as performance characteristics. Sadly, the changes described above inevitably decrease the weighting of performance characteristics in test selection. There is an enormous choice of test reagents, manufactured and/or supplied by different companies. For example, of the UK laboratories participating in the NEQAS scheme there were 19 diVerent cardiolipin tests, 13 TPHA/TPPA tests, nine EIAs, and seven FTA-abs in use (quoted with permission of the UK NEQAS organiser). It is important that laboratories do not change reagents frequently in order that they and their users such as genitourinary medicine physicians become fully conversant with the performance characteristics of the particular tests used. Published performance criteria following stringent evaluation in independent centres are available for very few of the numerous tests (and their modifications) produced by diVerent manufacturers. For example, there is a paucity Sex Transm Inf 2000;76:403–405 403