Wihokhoen Benchawan, Dondorp Arjen M, Turner Paul, Woodrow Charles J, Imwong Mallika
Am J Trop Med Hyg. 2016 Feb;94(2):322-326. doi: 10.4269/ajtmh.15-0532. Epub 2015 Dec 28.
Molecular approaches offer a means of testing archived samples stored as dried blood spots in settings where standard blood cultures are not possible. Peripheral blood films are one suggested source of material, although the sensitivity of this approach has not been well defined. Thin blood smears and dried blood spots from a severe pediatric malaria study were assessed using specific polymerase chain reaction (PCR) primers to detect non-typhoidal Salmonella (NTS; MisL gene), Streptococcus pneumoniae (lytA), and Plasmodium falciparum (18S rRNA). Of 16 cases of NTS and S. pneumoniae confirmed on blood culture, none were positive by PCR using DNA extracts from blood films or dried blood spots. In contrast, four of 36 dried blood spots and two of 178 plasma samples were PCR positive for S. pneumoniae, despite negative bacterial blood cultures, suggesting false positives. Quantitative assessment revealed that the effective concentration of P. falciparum DNA in blood films was three log orders of magnitude lower than for dried blood spots. The P. falciparum kelch13 gene could not be amplified from blood films. These findings question the value of blood PCR-based approaches for detection of NTS and S. pneumoniae, and show that stored blood films are an inefficient method of studying P. falciparum.
在无法进行标准血培养的情况下，分子方法提供了一种检测以干血斑形式保存的存档样本的手段。外周血涂片是一种建议的材料来源，尽管这种方法的敏感性尚未明确界定。使用特异性聚合酶链反应（PCR）引物对一项严重小儿疟疾研究中的薄血涂片和干血斑进行评估，以检测非伤寒沙门氏菌（NTS；MisL基因）、肺炎链球菌（lytA）和恶性疟原虫（18S rRNA）。在血培养确诊的16例NTS和肺炎链球菌病例中，使用血涂片或干血斑的DNA提取物进行PCR检测均为阴性。相比之下，尽管细菌血培养为阴性，但36个干血斑中有4个以及178个血浆样本中有2个肺炎链球菌PCR检测呈阳性，提示存在假阳性。定量评估显示，血涂片中恶性疟原虫DNA的有效浓度比干血斑低三个数量级。无法从血涂片中扩增出恶性疟原虫kelch13基因。这些发现质疑了基于血PCR方法检测NTS和肺炎链球菌的价值，并表明储存的血涂片是研究恶性疟原虫的低效方法。
