Objectives Australian HIV postexposure prophylaxis (PEP) guidelines recommend Chlamydia trachomatis (CT) and Neisseria gonorrheae (NG) testing at both baseline and 2-week postexposure visits. We aimed to determine the diagnostic yield of testing at one or more visits, and predictors of infection.
Methods Data were collected from patients prescribed PEP at RPA Sexual Health over a 4-year period from January 2008 to December 2011. Predictors of CT/NG were assessed by logistic regression.
Results 282 individuals presented for PEP on 319 occasions during the study period. The majority (94.3%) were male and over 90% of presentations followed unprotected anal sexual exposures. Most (279, 87.5%) had CT/NG testing at least once. Almost half (153, 48.0%) of baseline presentations, two-thirds (214, 67.1%) of 2-week presentations and over a quarter (88, 27.6%) of both presentations included CT/NG testing. CT/NG was diagnosed at baseline in eight (5.2%, 95% CI 2.3% to 10.0%) presentations. A new CT/NG diagnosis occurred at the 2-week visit in 18 (8.4%, 95% CI 5.1% to 13.0%) presentations, of whom 7 tested negative and 11 were not tested at baseline. Over one-quarter (28.1%) of PEP recipients reported sexual contact between baseline and 2-week visits. Independent predictors of CT/NG at baseline were recent sex work (OR 48.0, 95% CI 3.77 to 611.94); and at 2 weeks a known HIV-positive PEP exposure source (OR 3.54, 95% CI 1.04 to 12.06) and sex between baseline and 2-week visits (OR 3.63, 95% CI 1.10 to 11.96).
Conclusions Our findings suggest that screening PEP recipients for CT/NG at both baseline and 2 weeks may be warranted.
- CHLAMYDIA TRACHOMATIS
- NEISSERIA GONORRHOEA
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Australian HIV postexposure prophylaxis (PEP) guidelines1 recommend testing for Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) at both baseline and 2-week postexposure visits. US PEP guidelines2 recommend CT/NG testing at baseline, during and after the 28-day PEP course, whereas British PEP guidelines3 recommend CT/NG testing during and after the PEP course, but only at baseline if symptoms are present. To our knowledge, the diagnostic yield of CT/NG testing at specific time points after PEP exposures and the utility of repeat testing have never been formally assessed.
All patients prescribed PEP at RPA Sexual Health in Sydney over a 4-year period from January 2008 to December 2011 were identified from the clinic database. These individuals included those who received the initial course of PEP from RPA Sexual Health as well as those prescribed continuation of a PEP course at RPA Sexual Health after PEP initiation at another service. Data were abstracted from medical records and entered into an Excel database (Microsoft Corp, Redmond, Washington, USA).
CT/NG infections were initially diagnosed by strand displacement amplification (SDA) (BD ProbeTec, BD Diagnostics, Maryland, USA) with porA confirmation of non-genital SDA-positive N gonorrhoeae samples, as previously described.4 From October 2011, testing was performed using Aptima Combo 2 Transcription Mediated Amplification (Hologic Gen-Probe Inc, San Diego, California, USA).
Statistical analyses were performed using STATA V.12.0 (STATA Corporation, College Station, Texas, USA). Predictors of CT/NG testing and infection were assessed by logistic regression. Multivariate models were developed using forward stepwise regression. Since a number of individuals presented for PEP on multiple occasions during the study period, analyses were adjusted for repeated measures in the same individuals. Presentations with missing data were omitted from analyses. Quantitative variables were categorised as outlined in table 1. The study was approved by the Sydney Local Health District Ethics Review Committee.
There were 319 PEP presentations among 282 individuals during the study period. PEP was prescribed once to 249 (88.3%), twice to 29 (10.3%) and three times to 4 (1.4%) individuals. The majority (n=262, 94.3%) of PEP recipients were male, of whom 260 (99.2%) presented following a homosexual exposure. Characteristics of PEP presentations are outlined in table 1.⇓
Most (n=279, 87.5%) PEP presentations were tested for CT/NG at least once. Testing occurred at almost half (n=153, 48.0%) of baseline presentations, over two-thirds (n=214, 67.1%) of 2-week presentations and over a quarter (n=88, 27.6%) of presentations at both baseline and 2-week postexposure visits. Most (n=30, 75%) PEP presentations who were not tested for CT/NG at either baseline or 2-week visits had attended another clinic for their original PEP prescription, not returned for a scheduled follow-up visit or received follow-up elsewhere. Over 90% of PEP presentations by men who have sex with men (MSM) had testing at all recommended sites. At baseline, of 148 MSM presentations who had a urine CT/NG test, only 13 (8.8%) did not have anal testing and 11 (7.4%) did not have pharyngeal testing. At 2 weeks, of the 208 MSM presentations who had a urine CT/NG test, only 16 (7.7%) and 11 (5.3%) did not have anal and pharyngeal testing, respectively.
CT/NG testing at baseline was more common among those commencing PEP at RPA (vs another) clinic (p<0.001), those prescribed PEP during a more recent calendar year (p trend<0.001), males (p=0.003) and those with a known HIV-positive (vs unknown/known negative) exposure source (p=0.004). CT/NG testing at 2 weeks was more common among those reporting PEP side effects (p=0.003) and following a male homosexual (vs heterosexual) exposure (p=0.040).
All infections occurred in MSM. There were no CT/NG co-infections and no multi-site infections. Eight (5.2%, 95% CI 2.3% to 10.0%) infections were diagnosed at baseline screening: two pharyngeal and one anal NG infection; and two genital and three anal CT infections. Only the anal NG infection was symptomatic. The sole independent predictor of CT/NG infection at baseline was sex work in the past year (OR 48.0, 95% CI 3.77 to 611.94, p=0.003). However, this estimate was based on only three male sex workers of whom two tested positive at baseline.
A new CT/NG diagnosis occurred in 18 (8.4%, 95% CI 5.1% to 13.0%) presentations tested at 2 weeks. Of these 18 individuals, 7 (38.9%) had a negative test at baseline and 11 (61.1%) were not tested at baseline. One pharyngeal, four genital and six anal CT infections; and four pharyngeal and three anal NG infections were diagnosed. Only one genital CT infection was symptomatic. Independent predictors of a 2-week CT/NG diagnosis are shown in table 2.
Of 224 (70.2%) presentations where a repeat sexual history was provided at the 2-week visit, 63 (28.1%) reported sexual activity between the baseline and 2-week visit. Half (n=9) of the 2-week CT/NG diagnoses occurred in this group. Of those who reported sexual activity, 36 (57.1%) reported casual sexual partners, 15 (23.8%) reported multiple sexual partners and 9 (14.3%) reported unprotected anal or vaginal sex during this 2-week period.
There was no association between a CT/NG diagnosis at baseline or 2 weeks and: older age (p trend=0.913 and 0.323, respectively); more male sexual partners in the past year (p trend=0.255 and 0.124, respectively); or more frequent condom use in the past year for anal and/or vaginal sex with casual (p trend = 0.555 and 0.370, respectively) or regular (p trend=0.198 and 0.490, respectively) partners.
The prevalence of CT/NG identified among PEP recipients at our clinic was high, and similar to that reported at another clinic in Sydney.5 Sexual activity between visits was the strongest independent predictor of a new CT/NG diagnosis at the 2-week visit, suggesting at least some infections identified at 2 weeks were acquired after the PEP exposure. In fact, six of the seven individuals with potentially incident CT/NG reported sex between baseline and 2-week visits. An PEP exposure of sex with a known HIV-positive source was also independently associated with newly diagnosed CT/NG at 2 weeks. As HIV-positive gay men have high rates of sexually transmissible infections (STIs),6 it is also possible that some of these 2-week infections were acquired at the same time as the PEP exposure but that testing occurred too early to detect the infections.
Over 90% of CT/NG infections were asymptomatic, which underscores the importance of routine STI screening among individuals following a potential sexual risk exposure. As other STIs are known to facilitate HIV transmission,7 identification and treatment of curable STIs among high-risk individuals, such as PEP recipients, is an additional HIV prevention opportunity that should not be overlooked.
Our findings may not be generalisable to other populations of PEP recipients, especially where PEP is more commonly prescribed for heterosexual exposures. Testing of PEP recipients at both visits for CT/NG infection was not consistent, mainly due to non-attendance. Nonetheless, independent predictors of testing included factors associated with higher STI risk (eg, HIV-positive and male homosexual contact) suggesting that testing is being targeted to those at highest risk.
To our knowledge, this is the first study to investigate the optimal timing of CT/NG testing and the potential utility of a repeat testing approach in PEP recipients. The high number of new diagnoses at 2 weeks among those testing negative or not tested at baseline indicates potential for onward transmission of undiagnosed infections, especially as half of these individuals reported sexual activity between visits. Our findings suggest that screening PEP recipients for CT/NG at both baseline and 2 weeks may be warranted.
Among HIV postexposure prophylaxis (PEP) presentations, new chlamydia/gonorrhoea infections were diagnosed in over 5% at baseline and over 8% at the 2-week visit.
More than 90% of chlamydia/gonorrhoea infections identified were asymptomatic.
Half of those diagnosed with chlamydia/gonorrhoea at 2 weeks reported sex between baseline and 2-week visits, often with casual and/or multiple sexual partners.
Screening PEP recipients for chlamydia/gonorrhoea at both baseline and 2-week visits may be warranted.
Correction notice This article has been updated since it was published Online First. The citation in the sentence, ‘Independent predictors of a 2-week CT/NG diagnosis are shown in table 1.’ was corrected from ‘table 1’ to ‘table 2’.
Acknowledgements We wish to thank Chloe Dijanosic for assistance with the Excel database.
This work was presented at the 13th IUSTI World Congress, Melbourne, Australia, 15–17th October 2012 (Paper no. 633).
Contributors SJ: data collection, data interpretation and drafted the manuscript. TG: data collection, data interpretation and manuscript preparation. IMP: data interpretation and manuscript preparation. DJT: study concept, ethics, statistical analysis, assisted with drafting the manuscript, overall supervision of the project. All authors had full access to all of the study data and take responsibility for data integrity and accuracy of data analysis. DJT acts as guarantor for the study.
This work has not been submitted for publication elsewhere.
Competing interests None.
Ethics approval Sydney Local Health District Ethics Review Committee.
Provenance and peer review Not commissioned; externally peer reviewed.