Unité de Recherche Epidémiologique en Santé Périnatale et Santé des Femmes et des Enfants (U953), Inserm, Paris, France.
PLoS One. 2012;7(6):e39085. doi: 10.1371/journal.pone.0039085. Epub 2012 Jun 29.
The stability of the accuracy of a diagnostic test is critical to whether clinicians can rely on its result. We aimed to assess whether the performance of a rapid antigen detection test (RADT) for group A streptococcus (GAS) is affected by the clinical spectrum and/or bacterial inoculum size.
Throat swabs were collected from 785 children with pharyngitis in an office-based, prospective, multicenter study (2009-2010). We analysed the effect of clinical spectrum (i.e., the McIsaac score and its components) and inoculum size (light or heavy GAS growth) on the accuracy (sensitivity, specificity, likelihood ratios and predictive values) of a RADT, with laboratory throat culture as the reference test. We also evaluated the accuracy of a McIsaac-score-based decision rule.
GAS prevalence was 36% (95CI: 33%-40%). The inoculum was heavy for 85% of cases (81%-89%). We found a significant spectrum effect on sensitivity, specificity, likelihood ratios and positive predictive value (p<0.05) but not negative predictive value, which was stable at about 92%. RADT sensitivity was greater for children with heavy than light inoculum (95% vs. 40%, p<0.001). After stratification by inoculum size, the spectrum effect on RADT sensitivity was significant only in patients with light inoculum, on univariate and multivariate analysis. The McIsaac-score-based decision rule had 99% (97%-100%) sensitivity and 52% (48%-57%) specificity.
Variations in RADT sensitivity only occur in patients with light inocula. Because the spectrum effect does not affect the negative predictive value of the test, clinicians who want to rule out GAS can rely on negative RADT results regardless of clinical features if they accept that about 10% of children with negative RADT results will have a positive throat culture. However, such a policy is more acceptable in populations with very low incidence of complications of GAS infection.
诊断试验准确性的稳定性对于临床医生能否依赖其结果至关重要。我们旨在评估快速抗原检测试验（RADT）检测 A 组链球菌（GAS）的性能是否受临床谱和/或细菌接种量的影响。
在一项基于办公室的前瞻性多中心研究（2009-2010 年）中，我们从 785 例咽炎患儿中采集了咽喉拭子。我们分析了临床谱（即 McIsaac 评分及其组成部分）和接种量（轻度或重度 GAS 生长）对 RADT 准确性（敏感性、特异性、似然比和预测值）的影响，以实验室咽喉培养为参考试验。我们还评估了基于 McIsaac 评分的决策规则的准确性。
GAS 患病率为 36%（95%CI：33%-40%）。85%的病例接种量较重（81%-89%）。我们发现敏感性、特异性、似然比和阳性预测值（p<0.05）存在显著的谱效应，但阴性预测值没有，约为 92%。RADT 对接种量较重的患儿的敏感性大于接种量较轻的患儿（95%比 40%，p<0.001）。在按接种量分层后，仅在接种量较轻的患者中，基于单变量和多变量分析，RADT 敏感性的谱效应才有统计学意义。基于 McIsaac 评分的决策规则具有 99%（97%-100%）的敏感性和 52%（48%-57%）的特异性。
RADT 敏感性的变化仅发生在接种量较轻的患者中。由于谱效应不影响试验的阴性预测值，如果临床医生接受大约 10%的 RADT 阴性结果的患儿会有阳性咽喉培养结果，那么他们可以依靠 RADT 阴性结果排除 GAS，而无需考虑临床特征。然而，在 GAS 感染并发症发生率非常低的人群中，这种策略更易被接受。
