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Clinical sciences poster session 1: and related syndromes
P3-S1.26 Novel Chlamydia trachomatis point of care rapid test shows disappointingly low clinical sensitivity in urogenital Chlamydia infections in Paramaribo, Suriname
  1. J van der Helm1,
  2. L Sabajo2,
  3. S Morré3,
  4. A Grunberg4,
  5. A Speksnijder1,
  6. H de Vries5
  1. 1Health Service Amsterdam, Amsterdam, Netherlands
  2. 2Dermatology Service, Ministry of Health, Suriname
  3. 3VU University Medical Center, Netherlands
  4. 4Lobi Foundation, Suriname
  5. 5Health Service Amsterdam, Academic Medical Center, University of Amsterdam, Netherlands

Abstract

Background Affordable and reliable point of care (POC) tests to diagnose urogenital chlamydia infections (POC-Ct) are needed, especially in resource limited settings. WHO has formulated standards that POC tests have to meet. One of those is that the test should be sensitive. Three POC-Ct tests currently on the market all showed poor sensitivity between 12% and 17% in a non-manufacturer sponsored clinical study (van Dommelen 2010). One POC-Ct test evaluated in a manufacturer-sponsored study claims over 80% sensitivity (Mahilum-Tapay 2007). We evaluated the performance of this POC-Ct in two outpatient clinics in Suriname, S.A.

Methods Between July 2009 and February 2010 963 women were included in a high risk STI clinic (n=181) and a low risk birth control clinic (n=782) in Paramaribo, Suriname. Nurse collected vaginal swabs were obtained for the POC-Ct (Diagnostics for the Real World, LTD, Cambridge, UK) and control NAAT (APTIMA Combo 2, Gen-Probe, San Diego, USA) in a cross-over model. Swabs were processed according to the manufacturers instructions. POC-Ct was compared to NAAT and sensitivity, specificity, positive- and negative predictive value (PPV, NPV) were calculated. Quantitative Ct load was determined with a real-time PCR targeting the cryptic plasmid. Ct load was expressed as inclusion forming units (IFU) based on defined serial dilutions. An independent t-test was used to compare log-transformed Ct loads between true positive and false negative POC-Ct results.

Results Ct prevalence, determined by NAAT, was 23% at the high risk STI clinic and 9% at the low risk birth control clinic. Four samples were excluded due to discrepancy in POC-Ct result between two lab technicians (n=3) and failure of POC-Ct (n=1). Performance results of POC-Ct compared to NAAT are shown in Abstract P3-S1.26 table 1. Quantitative Ct bacterial load was 65 times higher when POC-Ct detected Ct infection (geometric mean 115 IFU) compared to loads that POC-Ct did not detect (geometric mean 1.8 IFU, p<0.001). Human DNA concentration did not differ between the true positive and false negative POC-Ct results (p=0.904). Sensitivity of POC-Ct in samples with low Ct load was 16%.

Abstract P3-S1.26 Table 1

Performance results of POC-Ct compared to NAAT

Conclusion The sensitivity and to a lesser extend the PPV of the POC-Ct did not meet the expectations as described previously (83.5%). The POC-Ct missed samples with a low Ct load. With a sensitivity of 41.7% the Diagnostics of the Real World POC-Ct test does not meet the ASSURED criteria of a sensitive test formulated by the WHO.

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