Lack of correlation between three commercial platforms for the evaluation of human immunodeficiency virus type 1 (HIV-1) viral load at the clinically critical lower limit of quantification.

BACKGROUND: Concordance in plasma HIV-1 viral load quantification at the lower limit of quantification (LLOQ) is crucial for current commercial assays. OBJECTIVE: To compare the performance of three commercial viral load assays and carry out a correlation study with the Roche Cobas AmpliPrep/Cobas TaqMan HIV-1 test, the Roche Cobas Amplicor HIV-1 MONITOR test, and the Abbott RealTime HIV-1 assay. STUDY DESIGN: Assay agreement was analyzed using linear regression and Bland-Altman plots. Concordance near the clinically critical LLOQ was measured by Cohen's kappa statistics. Intra-assay precision was assessed, and assay reproducibility was measured at 50copies/mL across all three platforms. RESULTS: While good overall correlation was observed between the assays (r≥0.93), quantitative differences exceeded 0.5log(10)copies/mL among paired results in 3.7 to 8.3% of specimens. The degree of concordance between the assays near the LLOQ was unsatisfactory, with Cohen's kappa ranging from 0.14 to 0.38. The intra-assay precision of the Abbott RealTime HIV-1 assay ranged from 0.04 to 0.15 (SD log(10)) and 1.34% to 8.37% (CV). Reproducibility at 50copies/mL for RealTime HIV-1, TaqMan, and Amplicor was 10.05, 11.04 and 5.07 (% CV), respectively. CONCLUSION: Although good correlation was observed between the assays across their linear range, their concordance at the clinically critical LLOQ was poor. The accurate quantification of low-level viremia remains elusive, and the lack of correlation of these assays presents a challenge to the interpretation of such results and in the clinical management of HIV-infected patients.

Prevalence, incidence and risk factors for pharyngeal gonorrhoea in a community-based HIV-negative cohort of homosexual men in Sydney, Australia.

BACKGROUND: Pharyngeal gonorrhoea is common in homosexual men and may be important in maintaining community prevalence of anogenital infections. METHODS: From 2003, all participants in the Health in Men cohort of HIV-negative homosexual men in Sydney were offered annual pharyngeal gonorrhoea screening by BD ProbeTec nucleic acid amplification (NAAT) assay with supplementary porA testing. Participants self-reported diagnoses of pharyngeal gonorrhoea made elsewhere between interviews. Detailed sexual behavioural data were collected 6-monthly. RESULTS: Among 1427 participants enrolled, 65 study-visit-diagnosed pharyngeal gonorrhoea infections were identified (incidence 1.51 per 100 person-years, 95% CI 1.19 to 1.93) of which seven infections were identified on baseline testing (prevalence 0.57%, 95% CI 0.23 to 1.17%). Almost 85% of study-visit-diagnosed pharyngeal infections occurred without concurrent anogenital gonorrhoea. The combined incidence of study-visit-diagnosed and self-reported pharyngeal gonorrhoea (n=193) was 4.45 per 100 person-years (95% CI 3.86 to 5.12). On multivariate analysis, incident infection was associated with younger age (p-trend=0.001), higher number of male partners (p-trend=0.002) and reported contact with gonorrhoea (p<0.001). Insertive oro-anal sex ('rimming') was the only sexual behaviour independently associated with incident pharyngeal gonorrhoea (p-trend=0.044). CONCLUSIONS: The majority of pharyngeal gonorrhoea occurred without evidence of concurrent anogenital infection, and the high incidence-to-prevalence ratio suggests frequent spontaneous resolution of NAAT-detected infection. The association of pharyngeal gonorrhoea with oro-anal sex indicates that a broader range of sexual practices are likely to be involved in transmission of gonorrhoea to the pharynx than previously acknowledged. Screening the pharynx of sexually active homosexual men could play a role in reducing the prevalence of anogenital Neisseria gonorrhoeae.

Low positive predictive value of a nucleic acid amplification test for nongenital Neisseria gonorrhoeae infection in homosexual men.

The diagnosis of nongenital Neisseria gonorrhoeae infection by the Becton Dickinson ProbeTec ET Chlamydia trachomatis and N. gonorrhoeae Amplified DNA assay had low positive predictive value among an Australian community-based sample of homosexual men. Only 30.4% of oropharyngeal samples and 73.7% of anorectal samples were positive for N. gonorrhoeae by the porA assay. The accuracy of nucleic acid amplification tests in this context is compromised without supplemental testing.