Objectives

1. WHEN DID THE NEW VARIANT OF CHLAMYDIA TRACHOMATIS (nvCT) EMERGE IN ÖREBRO COUNTY, SWEDEN? – A STATISTICAL EVALUATION OF THE POSITIVITY RATES FROM 1999 TO 2006 Margaretha Jurstrand 1, Per Olcén 2 , Anders Magnuson 3, Lena Jakobsson 2, Hans Fredlund 2, Magnus Unemo 2 Clinical Research Centre 1, Department of Laboratory Medicine, Clinical Microbiology 2, and Statistical and Epidemiology Unit 3, Örebro University Hospital, SE-70185 Örebro, Sweden Objectives In 2006 a new variant of Chlamydia trachomatis (nvCT), which escaped the diagnostic systems from Roche Diagnostics and Abbott Laboratories, was reported in Sweden (1). In most Swedish diagnostic laboratories only nucleic acid amplification tests (NAATs) are used for C. trachomatis detection. However, at Örebro University Hospital, analysing all C. trachomatisspecimens in Örebro County, both NAAT (Cobas Amplicor PCR, Roche) and tissue culture on McCoy cells are used. After the nvCT was identified, 38% of C. trachomatis culturepositives were confirmed as nvCT(2). nvCThas now been frequently detected across Sweden but it remains unknown where and when nvCT emerged. The aim of the present study was to compare the proportions of C. trachomatispositive specimens detected by NAAT to C. trachomatis positives by tissue culture from 1999 to 2006, in order to estimate when nvCT emerged in Örebro County, Sweden. Results Using CA PCR the proportion of C. trachomatis positive specimens decreased from 2002 to 2006 while the proportion of positive specimens using tissue culture, increased every year from 2001 to 2006 (Figure 1a), indicating a change during 2002 and 2003 (Figure 1b). The weighted linear regression showed a statistically significant interaction effect between years (1999 to 2006) and groups of specimens analysed with CA PCR or culture. Material and Methods For C. trachomatisdiagnosis, either Cobas Amplicor PCR (CA PCR), Roche or tissue culture (McCoy cells) with fluorescein-labeled monoclonal antibodies were used. The total number of specimens analysed using CA PCR from 1999 to 2006 were 5077, 5231, 6877, 7811, 8702, 10070, 11173, and 11643, respectively and using tissue culture 7425, 6615, 7133, 7311, 6446, 6148, 5482 and 5168, respectively. The percentage of C. trachomatis positive specimens for each year and method was calculated. Weighted linear regression was used to evaluate the change of proportion in C. trachomatis positive tests over the years between the two methods, and the statistical interaction effect of year and method was estimated. Figure 1a. Percentage of C. trachomatis positive tests in Cobas Amplicor PCR (CA PCR) and tissue culture with 95% confidence intervals from year 1999 to 2006. Figure 1b. Difference of percentage in C. trachomatis positive tests between CA PCR and tissue culture with 95% confidence intervals from year 1999 to 2006. Conclusions In Örebro County, Sweden, the nvCT may have emerged during 2002 to 2003, i.e. when the difference in proportions of C. trachomatispositive specimens in Cobas Amplicor PCR compared to tissue culture positive specimens, with statistical significance, began to decline. References 1. Ripa T and Nilsson, P. A Chlamydia trachomatis strain with a 377-bp deletion in the cryptic plasmid causing false negative nucleic acid amplification tests. Sex Transm Dis 2007. 34:255-56 2. Unemo M, Olcén P, Agné-Stadling I, et al.Experiences with the new genetic variant of Chlamydia trachomatis in Örebro county, Sweden - proportion, characteristics and effective diagnostic solution in an emergent situation. Euro Surveill 2007;12. Correspondence: margareta.jurstrand@orebroll.se