Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, United Kingdom.
PLoS Negl Trop Dis. 2019 Feb 4;13(2):e0007158. doi: 10.1371/journal.pntd.0007158. eCollection 2019 Feb.
Scrub typhus is a neglected tropical disease that causes acute febrile illness. Diagnosis is made based upon serology, or detection of the causative agent-Orientia tsutsugamushi-using PCR or in vitro isolation. The enzyme-linked immunosorbent assay (ELISA) is an objective and reproducible means of detecting IgM or IgG antibodies. However, lack of standardization in ELISA methodology, as well as in the choice of reference test with which the ELISA is compared, calls into question the validity of cut-offs used in diagnostic accuracy studies and observational studies.
METHODOLOGY/PRINCIPAL FINDINGS: A PubMed search and manual screening of reference lists identified 46 studies that used ELISA antibody cut-offs to diagnose scrub typhus patients, 22 of which were diagnostic accuracy studies. Overall, 22 studies (47.8%) provided little to no explanation as to how the ELISA cut-off was derived, and 7 studies (15.2%) did not even state the cut-off used. Variation was seen locally in reference standards used, in terms of both the diagnostic test and cut-off titer. Furthermore, with the exception of studies using ELISAs manufactured by InBios, there was no standardization of the selection of antigenic strains. As a result, no consensus was found for determining a cut-off, ELISA methodology, or for a single value diagnostic cut-off.
CONCLUSIONS/SIGNIFICANCE: We have concluded that there is a lack of consensus in the determination of a cut-off. We recommend interpreting the results from these studies with caution. Further studies will need to be performed at each geographic location to determine region-specific cut-offs, taking into consideration background antibody levels to discriminate true disease from healthy individuals.
恙虫病是一种被忽视的热带病，可引起急性发热疾病。诊断基于血清学，或使用 PCR 或体外分离检测病原体——恙虫东方体。酶联免疫吸附试验（ELISA）是检测 IgM 或 IgG 抗体的客观且可重复的方法。然而，ELISA 方法学以及与 ELISA 进行比较的参考测试选择缺乏标准化，这使得诊断准确性研究和观察性研究中使用的截止值的有效性受到质疑。
方法/主要发现：通过 PubMed 搜索和参考文献手动筛选，确定了 46 项使用 ELISA 抗体截止值诊断恙虫病患者的研究，其中 22 项为诊断准确性研究。总体而言，22 项研究（47.8%）几乎没有或根本没有解释 ELISA 截止值是如何得出的，而 7 项研究（15.2%）甚至没有说明使用的截止值。在参考标准的使用方面，局部存在差异，无论是诊断测试还是截止滴度。此外，除了使用 InBios 制造的 ELISA 的研究外，在抗原菌株的选择方面没有标准化。因此，无法就确定截止值、ELISA 方法学或单个诊断截止值达成共识。
结论/意义：我们得出的结论是，在确定截止值方面缺乏共识。我们建议谨慎解释这些研究的结果。需要在每个地理位置进行进一步的研究，以确定特定于该地区的截止值，同时考虑到背景抗体水平，以区分真正的疾病与健康个体。
