Background Ctis globally the most common cause of sexually transmitted infections. A new variant of ct with a deletion in the cryptic plasmid has been found in Sweden, following an unexpected 25% increase in genital infections in 2006. This variant escapes routine diagnostic PCR-tests. Thus a new nuclear acid amplification test (NAAT), which uses the cryptic plasmid as well as the MOMP-gene as target area was developed. The MOMP-gene encodes a protein (OMP-1) which represents 60% of the proteins embedded in the peptidoglycans of the bacterial cell wall. The aim of this study was to define the number of cryptic plasmid-/MOMP+ patients.

Methods Between 2009 to 2012 we analysed probes of 11250 individuals (patients and controls) processing the ProbeTecET^® test (BD, USA). Of these 407 showed a positive result and were treated according to current guidelines. 33 patients tested negative, however, reported a persistence of discomfort such as burning sensations in the urethra, urethral discharge and occasionally conjunctivitis. These patients were additionally tested with the GenoQuick^® CT (HAIN Lifescience, Germany), which specifically and simultaneously detects both, the MOMP-gene and the cryptic plasmide. Material was taken from urethral, cervical, rectal, pharyngeal, conjunctival smears and from the Douglas-space.

Results All 33 patients tested positive when processing the GenoQuick® CT. Thus 7.5% of infected patients were only identified processing an additional detection set.

Conclusion In our centre 7.5% of ct infected patients were tested “false negative” when only the cryptic plasmide was analysed. These 33 patients were identified processing a more sensitive test system and subsequently were treated.