Comparison of two Gram stain point-of-care systems for urogenital gonorrhoea among high-risk patients: diagnostic accuracy and cost-effectiveness before and after changing the screening algorithm at an STI clinic in Amsterdam

Objectives To compare point-of-care (POC) systems in two different periods: (1) before 2010 when all high-risk patients were offered POC management for urogenital gonorrhoea by Gram stain examination; and (2) after 2010 when only those with symptoms were offered Gram stain examination. Methods Retrospective comparison of a Gram stain POC system to all high-risk patients (2008–2009) with only those with urogenital symptoms (2010–2011) on diagnostic accuracy, loss to follow-up, presumptively and correctly treated infections and diagnostic costs. Culture was the reference diagnostic method. Results In men the sensitivity of the Gram stain was 95.9% (95% CI 93.1% to 97.8%) in 2008–2009 and 95.4% (95% CI 93.7% to 96.8%) in 2010–2011, and in women the sensitivity was 32.0% (95% CI 19.5% to 46.7%) and 23.1% (95% CI 16.1% to 31.3%), respectively. In both periods the overall specificity was high (99.9% (95% CI 99.8% to 100%) and 99.8% (95% CI 99.7% to 99.9%), respectively). The positive predictive value (PPV) and negative predictive value (NPV) before and after 2010 were also high: PPV 97.0% (95% CI 94.5% to 98.5%) and 97.7% (95% CI 96.3% to 98.6%), respectively; NPV 99.6% (95% CI 99.4% to 99.7%) and 98.8% (95% CI 98.5% to 99.0%), respectively. There were no differences between the two time periods in loss to follow-up (7.1% vs 7.0%). Offering Gram stains only to symptomatic high-risk patients as opposed to all high-risk patients saved €2.34 per correctly managed consultation (a reduction of 7.7%). Conclusions The sensitivity of the Gram stain is high in men but low in women. When offered only to high-risk patients with urogenital symptoms, the cost per correctly managed consultation is reduced by 7.7% without a significant difference in accuracy and loss to follow-up.