Which is the best method?
—Tests for SARS-CoV-2 Infection Diagnosis
For confirmed COVID-19 cases, reported the common clinical symptoms include fever,cough,myalgia or fatigue. Yet these symptoms are not unique features of COVID-19 because these symptoms are similar to that of other virus-infected disease such as influenza. Currently, virus nucleic acid Real-Time PCR (rt-PCR), CT imaging and some hematology parameters are the primary tools for clinical diagnosis of the infection. Many laboratory test kits have been developed and used in testing patient specimens for COVID-19 by Chinese CDC1, US CDC2 and other private companies. IgG/IgM antibody test, a serological test method, has also been added as a diagnostic criteria in China's updated version of the diagnosis and treatment guidelines for the novel coronavirus disease (COVID-19), which was issued on 3rd, March1. The virus nucleic acid rt-PCR test still is the current standard diagnostic method for diagnosis of COVID-19.
StrongStep® Novel Coronavlrus (SARS-COV-2)Multiplex Real-Time PCR Kit(detection for three genes)
Yet these real-time PCR test kits, looking for genetic material of the virus, for instance in nasal, oral, or anal swabs, suffer from many limitations:
1) These tests have long turnaround times and are complicated in operation; they generally take on average over 2 to 3 hours to generate results.
2) The PCR tests require certified laboratories, expensive equipment and trained technicians to operate.
3) There are some numbers of false negatives for rt-PCR of COVID-19. It may due to low SARS-CoV-2 viral load in the upper respiratory swab specimen( Novel coronavirus mainly infects the lower respiratory tract, such as pulmonary alveoli ) and the test can’t identify people who went through an infection, recovered, and cleared the virus from their bodies.
Research by Lirong Zou et al4 found that higher viral loads were detected soon after symptom onset, with higher viral loads detected in the nose than in the throat and the viral nucleic acid shedding pattern of patients infected with SARS-CoV-2 resembles that of patients with influenza4 and appears different from that seen in patients infected with SARS-CoV-2.
Yang Pan et al5 examined serial samples (throat swabs, sputum, urine, and stool)from two patients in Beijing and found that the viral loads in throat swab and sputum samples peaked at around 5–6 days after symptom onset, sputum samples generally showed higher viral loads than throat swab samples. No viral RNA was detected in urine or stool samples from these two patients.
PCR test only give a positive result when the virus is still present. The tests can't identify people who went through an infection, recovered, and cleared the virus from their bodies. In acturely, only about 30%-50% was positive for PCR in patients with clinically diagnosed novel coronavirus pneumonia. Many novel coronavirus pneumonia patients can not be diagnosed because of negative nucleic acid test, so they can not get the corresponding treatment in time. From the first to the sixth edition of the guidelines, relying solely on the basis of the diagnosis of nucleic acid test results, which caused great trouble to clinicians.The earliest "whistle-blower", Dr. Li Wenliang, an ophthalmologist at Wuhan Central Hospital, is dead. During his lifetime, he had three nucleic acid tests in the case of fever and cough, and the last time he got PCR positive results.
After discussion by experts, it was decided to increase serum testing methods as a new diagnostic criterion. While antibody tests, also called serological tests, that can confirm whether someone was infected even after their immune system has cleared the virus that causes COVID-19.
StrongStep® SARS-COV-2 IgG/IgM Antibody Rapid Test
IgG/IgM antibody test will help to trace in a much more population-based way who has had the infection, because many cases seem to be spread from asymptomatic patients who can’t be identified easily. A couple in Singapore, the husband tested positive by PCR, his wife's PCR test result was negative, but the antibody test results showed that she had antibodies, as did her husband.
Serological assays need to be carefully validated to be sure they react reliably, but only to antibodies against the novel virus. One concern was that the similarity between the viruses that cause severe acute respiratory syndrome and COVID-19 could lead to cross-reactivity. The IgG-IgM developed by Xue Feng wang6 was considered to be able to be used as a point-of-care test (POCT), as it can be performed near the bedside with fingerstick blood. The kit has sensitivity of 88.66% and specificity of 90.63%. However, there were still false positive and false negative results.
In China's updated version of the diagnosis and treatment guideline for the novel coronavirus disease (COVID-19)1, confirmed cases are defined as suspected cases who meet any one of the following criteria:
(1)Respiratory tract samples,blood or stool specimens tested positive for SARS-CoV-2 nucleic acid using rt-PCR;
(2)Genetic sequencing of virus from respiratory tract,blood or stool specimens samples is highly homologous with the known SARS-CoV-2;
(3)Serum novel coronavirus specific IgM antibody and IgG antibody were positive;
(4)Serum novel coronavirus-specific IgG antibody changed from negative to positive or coronavirus-specific IgG antibody during recovery period is 4 times higher than that during the acute period.
Diagnosis and treatment of COVID-19
|
Guidelines |
Pubished |
Confirmed diagnostic criteria |
|
Version 7th |
3Mar.2020 |
❶ PCR ❷ NGS ❸ IgM+IgG |
|
Version 6th |
18 Feb.2020 |
❶ PCR ❷ NGS |
Reference
1. Guidelines for diagnosis and treatment of novel coronavirus pneumonia (trial version 7, National Health Commission of the People's Republic of China, issued at 3.Mar.2020)
http://www.nhc.gov.cn/yzygj/s7652m/202003/a31191442e29474b98bfed5579d5af95.shtml
2. Research Use Only Real-Time RT-PCR Protocol for Identification of 2019-nCoV
https://www.cdc.gov/coronavirus/2019-ncov/lab/rt-pcr-detection-instructions.html
3. Singapore claims first use of antibody test to track coronavirus infections
https://www.sciencemag.org/news/2020/02/singapore-claims-first-use-antibody-test-track-coronavirus-infections
4.SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients February 19,2020 DOI: 10.1056/NEJMc2001737
5.Viralloads of SARS-CoV-2 in clinical samples Lancet Infect Dis 2020 Published Online February 24, 2020 (https://doi.org/10.1016/S1473-3099(20)30113-4)
6. Developmentand Clinical Application of A Rapid IgM-IgG Combined Antibody Test for SARS-CoV-2
Infection Diagnosis XueFeng Wang ORCID iD: 0000-0001-8854-275X
Post time: Mar-17-2020
