Florou Zoe, Zigra Meropi, Kartalidis Philippos, Tsilipounidaki Katerina, Papadamou Georgia, Belia Aikaterini, Fthenakis George C, Petinaki Efthymia
Department of Microbiology, University Hospital, University of Thessaly, 41110 Larisa, Greece.
Department of Emergency, University Hospital, University of Thessaly, 41110 Larisa, Greece.
Microorganisms. 2021 Jun 10;9(6):1263. doi: 10.3390/microorganisms9061263.
The objective of the present study was to evaluate the true positivity among people, whose results of initial testing of nasopharyngeal swabs (NPS) showed a very low viral load of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Seventy-seven people detected with low viral loads of SARs-CoV-2 in nasopharyngeal samples (Ct ≥ 35) were enrolled in the study. For this purpose, a second NPS was collected for rRT-PCR (real-time reverse transcription polymerase chain reaction) combined with a pair of serum samples for detection of anti-nucleocapsid (anti-N) and anti-spike (anti-S) antibodies. In 8 people, subsequent examinations indicated an increase in viral loads, thereafter, followed by an increase of anti-N and anti-S antibodies, findings compatible with an early stage of COVID-19 infection. In 9 people, who already had increased anti-N antibodies, subsequent examination showed a decrease or absence of viral load and an increase in antibodies, indicative of a late stage of COVID-19 infection. In 60 people, subsequent examination showed absence of infection (as indicated by absence of viral load and antibodies). We propose that the combination of a second NPS and one serum-specimen, both taken three days after the first NPS, helps significantly to avoid false-positive results.
本研究的目的是评估鼻咽拭子（NPS）初始检测结果显示严重急性呼吸综合征冠状病毒2（SARS-CoV-2）病毒载量极低的人群中的真阳性情况。77名鼻咽样本中SARS-CoV-2病毒载量较低（Ct≥35）的人被纳入该研究。为此，采集第二份NPS进行逆转录聚合酶链反应（rRT-PCR），并采集一对血清样本检测抗核衣壳（抗N）和抗刺突（抗S）抗体。在8人中，后续检测显示病毒载量增加，随后抗N和抗S抗体增加，这些结果与COVID-19感染早期相符。在9名已经抗N抗体增加的人中，后续检测显示病毒载量降低或消失且抗体增加，表明处于COVID-19感染后期。在60人中，后续检测显示未感染（病毒载量和抗体均未检出）。我们建议，在首次采集NPS三天后采集第二份NPS和一份血清样本，这有助于显著避免假阳性结果。
