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Chlamydia point-of-care testing: where are we now?
  1. Anu Jain,
  2. Catherine A Ison
  1. Sexually Transmitted Bacteria Reference Unit, Microbiology Services, Health Protection Agency, London, UK
  1. Correspondence to Professor Catherine A Ison, Sexually Transmitted Bacteria Reference Unit, Microbiology Services, Health Protection Agency, 61 Colindale Avenue, London NW9 5EQ, UK; Catherine.ison{at}hpa.org.uk

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Healthcare delivery systems are rapidly evolving, and in the present economic environment, accurate and cost effective point-of-care (POC) tests are a way forward to achieve immediate laboratory diagnosis for sexually transmitted infections (STIs) including chlamydia. However, a robust and reliable POC test for genital chlamydia infection is yet to become available. This editorial describes what constitutes an ideal POC test, highlights issues about introducing POC testing for chlamydia in resource-rich countries like the UK, and also summarises the finding of various studies in this area.

The Medicines and Healthcare products Regulatory Agency defines POC testing as ‘any analytical test performed for a patient by a healthcare professional outside the conventional laboratory setting’.1 This does not incorporate direct testing by the consumers at home.1 The POC tests for STIs should ideally meet the ‘ASSURED’ criteria (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free and delivered).2 These tests are being used in haematology and biochemistry; for infectious diseases, POC testing has been successfully used for HIV, malaria and syphilis.3 At present, such an ‘ASSURED’ POC test does not exist for chlamydia.

In the UK, genital Chlamydia trachomatis (CT) continues to be the most frequent treatable bacterial STI. Asymptomatic chlamydia infection can maintain onward transmission unless detected by screening and subsequently treated. The highest prevalence of chlamydia infection is seen in young adults of <25 years of age, the target group for the National Chlamydia Screening Programme (NCSP), launched in 2003.

In a recent publication, the overall diagnosis rate in this screening population fell by 4% (from 2246 to 2148 per 100 000 population between 2010 and 2011); this was mainly attributed to decreased testing in community settings.4 This is concerning, as early diagnosis and treatment not only prevents complications but also stops further spread. Hence, testing is a crucial part of any effective control strategy.

Presently in the UK, the mainstay of chlamydia diagnostics continue to be nucleic acid amplification tests (NAATs) which are laboratory based and are more sensitive and specific than enzyme immunoassay (EIA). The turnaround time for NAATs varies from a few hours to a few days and offers the advantage of simultaneous testing for gonorrhoea. The delay between testing and results leads to a risk of onward transmission, later treatment and partner notification; requires a second visit and possible non-returns during this period. It is due to this delay that availability of a POC testing with immediate diagnosis and management is attractive to care providers, commissioners and users. Most POC tests available for chlamydia are EIA-based immunochromatography methods which detect antigen or antibody in the sample, leading to a colour change. With advances in miniaturisation of laboratory systems, technology, genomics and proteomics, development of new and better POC tests is anticipated.

For countries like the UK, genitourinary medicine (GUM) clinics and the NCSP already work in close association with diagnostic laboratories, and one can argue that introduction of POC tests may not necessarily be cost effective. However, the NCSP data shows wide variation in the proportion of the index patients reported to have received treatment from 56.2% to 100% for the period April 2011 to December 2011.5 Hence, ‘ASSURED’ POC tests will provide more choice and convenience, and be particularly useful in those settings where patient non-returns and subsequent treatment are recognised problems.

Introduction of any POC test in the present healthcare delivery systems will warrant investment, a thorough assessment of clinical need, and effects on care pathways. Robust quality assurance and clinical governance systems will be obvious prerequisites.

Assessment of the diagnostic accuracy of POC tests requires careful and systematic examination of available evidence. The Conformité Européenne (CE) mark on the POC tests is a declaration by the manufacturer that the product meets the Essential Requirements of three European Directives and should not be taken as a guarantee for accuracy. This was illustrated in a study from The Netherlands that compared three CE-marked POC tests (one enzymatic and other two antigen tests) for diagnostic performance in a high CT-prevalence population (11%), compared with NAATs over an 8-month period.6 The sensitivity of the tests was disappointing, and ranged from 12% to 27% in 772 women tested. A different study from the Philippines also found poor performance of a CE-marked POC test compared with NAATs in the obstetric-gynaecology clinic (mainly pregnant women for antenatal care, CT prevalence 8%) and social hygiene clinic (mainly commercial sex workers, CT prevalence 23.7%), with sensitivity of 12.5% and 19.4% and specificity of 93.5% and 88%, respectively.7

With regards to diagnostic accuracy, a systematic review that included 13 studies and enrolled 8817 subjects found Chlamydia Rapid Test (CRT) compared with a NAAT had sensitivity (95% CI) of 77% (59–89%) for first-void urine specimens, and 80% (73–85%) for vaginal swabs with specificity (95% CI) of 99% (98–99%) and 99% (99–100%), respectively.8 In this review, due to lack of evidence, a review of effectiveness of POC tests compared with PCR in terms of number of cases and contacts identified and treated could not be performed.

Although instinctively a more accurate POC test appears to be a prerequisite, a US study by Gift et al9 (‘rapid test paradox’) found that a rapid test with sensitivity of 63% would result in treating more patients compared with PCR with sensitivity of 94% if the return rate fell below 65% in an area with chlamydia prevalence of 8% in a hypothetical cohort of 10 000 women. In another study, advantages of using POC test in women attending the UK GUM clinics were evident if either the return rate was very low or the POC test was nearly as sensitive as the NAATs.10

Patient acceptability is an obvious requirement before making any POC tests mainstream. Patient acceptability outcomes compiled by a review showed willingness to wait for <30 min for POC test results in 54% of patients (n=2378) with 38% willing to wait between 30–120 min.8

With regards to cost effectiveness of POC tests compared with PCR, a deterministic model assuming chlamydia prevalence of 7.8% and partner notification rate of 98% found PCR to identify more true positive cases compared with the two POC tests (CRT and Clearview Chlamydia) and was least expensive in a cohort of 1000 people (aged 16–24 years). However, CRT was shown to be more cost effective if the acceptance rate was increased compared with PCR, and the cost of the POC test reduced.8

To conclude, an ‘ASSURED’ POC test for chlamydia is yet to become available. Currently available POC tests are limited by their performance and cost. Further studies are required to assess the ‘rapid test paradox’; patient and staff acceptability.

References

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Footnotes

  • Contributors CAI initiated this work, AJ undertook the review of existing data and prepared the manuscript, AJ and CI edited and approved the final manuscript.

  • Competing interests None.

  • Provenance and peer review Commissioned; internally peer reviewed.

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