Background Syphilis has made a major comeback in China, now representing the most common communicable disease in many cities and regions. A total of 327 433 cases of syphilis were reported in 2009, accounting for a sevenfold increase since 1999. Accurate treponemal and non-treponemal serological testing are critical to providing a correct diagnosis, but there are substantial variations in the quality of serological diagnostic tests and testing across different parts of China. Since 2003, the Guangdong Provincial STI Control Center in collaboration with the Bureau of Public Health has developed a program on STIs laboratory construction and quality assurance system. We report the proficiency of serological test of syphilis among the STIs laboratories in Guangdong Province in 2004–2009.
Methods Proficiency panels consisting of five samples with syphilis positive and negative sera were prepared in the provincial laboratory and sent to STIs laboratories for non-treponemal and treponemal testing once a year. Participating laboratories were asked to report the type of test used and quantitative and qualitative results for each serum. Each quantitative result was compared to the geometric mean of all participants' results, and was considered correct if it was less than fourfold difference from the mean titre.
Results The numbers of STIs laboratories in Guangdong which participated in the survey increased from 19 to 225 and a total of 13 203 sera were tested from 2004 to 2009. 98% laboratories used the “toluidine red unheated serum” (TRUST) as their non-treponemal test and all laboratories used the “Treponema pallidum particle agglutination assay” (TPPA) as their treponemal test. The mean accuracies of non-treponemal tests among the laboratories evaluated increased significantly from 78.9% in 2004 to 97.7% in 2009 (χ2=17.11, p<0.01) for qualitative test results, and from 75.8% in 2004 to 90.8% in 2009 (χ2=8.09, p<0.01) for quantitative test results. Higher accuracies were observed with TPPA ranging from 93.5 to 100% (χ2=2.85, p>0.05) for qualitative test results and improved from 73.7% to 86.5% (χ2=4.7, p<0.05) for quantitative test results during this period. For non-treponemal testing, 4.1% (113/2754) of the results were found to be false negative and 2.3% (34/1456) were found to be false positive. For qualitative treponemal results, 6.5% (96/1470) and 1.9% (17/889) of treponemal results were found to be false-negative and false-positive respectively. For quantitative results, it was worth noting that in some cases, four to seven-titre deviations were observed for the same sera.
Conclusion This province-wide STIs laboratory construction and quality assurance system has helped to improve the accuracies of serological syphilis testing over time. But there is still room for improvement to facilitate improved control of syphilis in China.
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