High occurrence of a new variant of Chlamydia trachomatis escaping diagnostic tests among STI clinic patients in Stockholm, Sweden.
BACKGROUND
In 2006, a genetic variant of Chlamydia trachomatis not detectable with the most commonly used diagnostic tests was identified. Initial reports suggested that as many as 10% to 13% of all chlamydia cases would have remained undiagnosed. The aim of the study was to find the occurrence and clinical findings of this genetic variant among a high-risk population in Stockholm, Sweden.


METHODS
Samples were analyzed using the Cobas TaqMan CT test (Roche Diagnostics). To detect the new variant, an additional PCR-analysis, artus C. trachomatis LC MOMP PCR Kit (Qiagen) was performed on all negative samples. Positive results in the artus test were confirmed by a mutant specific PCR. Clinical data were retrospectively collected from medical records.


RESULTS
Among 1009 samples analyzed, 115 were positive for C. trachomatis and among those, 27 were found to belong to the genetic altered strain. This variant constituted 23% of all chlamydia cases diagnosed, and 29% were found in the age group 20 to 29 years. Women with the new variant were younger and had more often performed another chlamydia test within the previous 6 months compared with those infected with the wild type.


CONCLUSIONS
These results indicate that a large number of sexually active individuals might be infected despite a negative chlamydia test, thus facilitating a rapid transmission of the new variant. Accordingly, it is of great importance to be aware of limitations of the diagnostic methods used.
Marions
Lena
L
Division of Obstetrics and Gynaecology, Department of Woman and Child Health, Karolinska Institutet/Karolinska University of Hospital, Stockholm, Sweden. lena.marions@karolinska.se
Rotzen-Ostlund
Maria
M
Grillner
Lena
L
Edgardh
Karin
K
Tiveljung-Lindell
Annika
A
Wikstrom
Arne
A
Lidbrink
Peter
P
D000293:Adolescent; D000328:Adult; D000368:Aged; D000554:Ambulatory Care Facilities; D002690:Chlamydia Infections / Q000175:diagnosis* / Q000453:epidemiology* / Q000209:etiology / Q000517:prevention & control / Q000652:urine; D002692:Chlamydia trachomatis / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification; D004269:DNA, Bacterial / Q000032:analysis; D003951:Diagnostic Errors / Q000706:statistics & numerical data; D003955:Diagnostic Tests, Routine / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016133:Polymerase Chain Reaction / Q000706:statistics & numerical data; D011237:Predictive Value of Tests; D011933:Reagent Kits, Diagnostic / Q000706:statistics & numerical data*; D013548:Sweden / Q000453:epidemiology; D014521:Urethra / Q000382:microbiology; D014626:Vaginal Smears
D004269:DNA, Bacterial; D011933:Reagent Kits, Diagnostic