Key points of the research

• The newly developed rapid testing kit detects COVID-19 antibodies, achieving results in 15 minutes with only a micro-liters of serum.
• The antibody detection kit will serve as a point-of-care testing device and may compensate for the limitations of a PCR-based diagnosis.
• Its unique fluorescence-based semi-quantitative measurement makes possible precise judgment of results and fine-tuning of cutoff values.
• Results from a pilot trial suggests that positivity for COVID-19 antibody may be as high as 1% among Osaka citizens.

Overview

On April 15, 2020, a research group from Osaka City University (OCU) launched a clinical trial to investigate the performance and clinical efficacy of a newly developed COVID-19 antibody detection kit. The study is being led by Associate Professor Yasutoshi Kido, Lecturer Yu Nakagama and Professor Akira Kaneko from the Department of Parasitology, as well as Professor Hiroshi Kakeya from the Department of Infection Control Science and Professor Yasumitsu Mizobata from the Department of Traumatology and Critical Care Medicine, using a testing platform developed in collaboration with Mokobio Biotechnology R & D Center Inc.

The current, most widely used method for COVID-19 testing is based on PCR technology. However, PCR-based diagnoses still harbor issues with accuracy, procedural simplicity, and cost-effectiveness. The high prevalence of mildly symptomatic or even asymptomatic patients causing the explosive spread of COVID-19 calls for an alternative to PCR-based testing in order for us to cope against this emerging infectious disease. To compensate for the limitations of a PCR-based diagnosis, the research group proposes a novel method which monitors the intensity of the host immune response, by measuring human serum antibody titer specific to the SARS-CoV2 virus.

Human host immune cells are capable of producing “antibodies” which specifically capture proteins originating from infectious viruses. If not infected with the COVID-19 causing SARS-CoV2, antibodies against SARS-CoV2 derived proteins will be absent from the blood. The IgM antibody usually appears during the early stage of infection and the IgG antibody will follow as the illness shifts towards the recovery stage. Testing for various COVID-19 antibodies has the potential to efficiently diagnose and further estimate the stage of disease.

By its unique fluorescence-based semi-quantitative detection system, the novel method avoids inter-observer judgment errors by digitizing the measurement process. The amount of blood needed for testing is as small as 20 μL. Avoiding the need to obtain nasopharyngeal swab specimens reduces the risk of infection among medical personnel who are responsible for patients’ sample collection.

In their pilot trial, the researchers randomly sampled residual serum specimens from the OCU outpatient clinic and investigated the rate of positivity for the COVID-19 IgG antibody (“seropositivity”). Among 312 participants who all had visited the hospital for non-COVID-19 purposes, the anti-SARS-CoV2 IgG antibody was present in three, representing up to approximately 1% (median 0.96, IQR 0.33–2.8%). Although limitations exist in extrapolating the finding to the IgG prevalence among healthy Osaka citizens, they state that the reported number of PCR-confirmed symptomatic cases may only represent the tip of an iceberg of the whole burden of infection. By scaling up the surveys, the test will also help in better visualizing the regional differences of the COVID-19 health impact. Existing data regarding the symptomatology and severity of COVID-19 indicate regional variability (e.g. Japan showing a strikingly low rate of deaths compared to some European countries), and better understanding the epidemiology will elucidate the actual clinical picture.

The research group states that antibody testing conveys substantial advantages over PCR-based diagnoses when used as screening measures on travelers, at fever clinics and/or emergency departments. Aside from developing a reliable, ready-for-use diagnostic tool and enhancing healthcare resilience, the current research project further aims to elucidate COVID-19 pathophysiology, by clarifying the relationship between the patients’ clinical data and their antibody responses during the time-course of COVID-19.

Moreover, fragile health-care systems in resource limited, low- or mid-income countries are sure to face increasing difficulties in medical decision making. Researchers are convinced that their point-of-care testing device will perfectly fit into such settings, where healthcare systems rely heavily on mobile medical units or local clinics. Through collaboration with their partners from the low- or mid-income countries, the group hopes to help implement this validated testing device so as to improve the preparedness of those countries for the pandemic.

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