Validation of a combined ELISA to detect IgG, IgA and IgM antibody responses to SARS-CoV-2 in mild or moderate non-hospitalised patients

BACKGROUND

Frequently SARS-CoV-2 results in mild or moderate disease with potentially lower concentrations of antibodies compared to those that are hospitalised. Here, we validated an ELISA using SARS-CoV-2 trimeric spike glycoprotein, with targeted detection of IgG, IgA and IgM (IgGAM) using serum and dried blood spots (DBS) from adults with mild or moderate disease.

METHODS

Targeting the SARS-CoV-2 trimeric spike, a combined anti-IgG, IgA and IgM serology ELISA assay was developed using 62 PCR-confirmed non-hospitalised, mild or moderate COVID-19 samples, ≥14 days post symptom onset and 624 COVID-19 negative samples. The assay was validated using 73 PCR-confirmed non-hospitalised, mild or moderate COVID-19 samples, ≥14 days post symptom onset and 359 COVID-19 negative serum samples with an additional 81 DBSs. The assay was further validated in 226 PCR-confirmed non-hospitalised, mild or moderate COVID-19 samples, ≥14 days post symptom onset and 426 COVID-19 negative clinical samples.

RESULTS

A sensitivity and specificity of 98.6% (95% CI, 92.6-100.0), 98.3% (95% CI, 96.4-99.4), respectively, was observed following validation of the SARS-CoV-2 ELISA. No cross-reactivities with endemic coronaviruses or other human viruses were observed, and no change in results were recorded for interfering substances. The assay was stable at temperature extremes and components were stable for 15 days once opened. A matrix comparison showed DBS to correlate with serum results. Clinical validation of the assay reported a sensitivity of 94.7% (95% CI, 90.9-97.2%) and a specificity of 98.4% (95% CI, 96.6-99.3%).

CONCLUSIONS

The human anti-IgGAM SARS-CoV-2 ELISA provides accurate and sensitive detection of SARS-CoV-2 antibodies in non-hospitalised adults with mild or moderate disease. The use of dried blood spots makes the assay accessible to the wider community.

Middle ear gas composition during nitrous oxide-oxygen ventilation

The middle ear gas composition during 180 minutes ventilation with nitrous oxide-oxygen mixture was determined in 12 mongrel dogs. The mean relative concentration of N2O in the middle ear (ME) rose to 12,26.4 and 29.3% after 60, 120 and 180 minutes respectively. During this period, the relative concentration of N2 dropped from a mean of 83.2% in the air-ventilated dogs to 54.8%, without an essential change in the concentrations of O2 or CO2. The elimination of N2O from the ME during 30 minutes of postanesthetic ventilation with O2 was incomplete, an average of 11.4% N2O remaining in the ME. At the same time, the mean relative concentration of O2 reached 19%, higher than the O2 relative concentration normally present in the ME. The results indicate that gas diffusion may occur across the ME mucosa for N2O as well as for O2, producing selective changes in the middle ear gas composition.

The middle ear gas composition in air-ventilated dogs

The middle ear gas composition has been examined in 5 air-ventilated dogs under sodium thiopentone anesthesia. The gas samples were obtained by transtympanic puncture and analysed by gas chromatography. The following mean +/- S.D. gas composition was obtained: N2 83.2 +/- 5.0; O2 12.1 +/- 2.2; and CO2 4.7 +/- 0.7.

Micromethod for determination of middle ear gas composition

This is a microchromatographic method for simultaneous determinations of O2, N2, CO2 and N2O in gas samples of 40-100 microliters. A Packard 836 U gas chromatograph with a thermal conductivity detector and helium gas as carrier was used. The combination of Porapak and 5A molecular sieve column system was found adequate and is described in detail. The fidelity of this method was proved by a high constancy of the retention time, the linearity of the response and the reproducibility of results. The present method proved to be reliable for determination of all middle ear gases in man and experimental animals during general anesthesia with N2O.

Oral phenylalanine and tyrosine tolerance tests in Parkinsonian patients

Reduction of dopamine concentrations in the brains of patients with Parkinsonism, together with reported clinical improvement after the administration of dihydroxyphenylalanine, has led to the hypothesis that impaired hydroxylation of tyrosine may be associated with the disease. To test this hypothesis oral loading tests with L-phenylalanine and tyrosine were carried out in patients and controls. After phenylalanine lower blood levels of this were found in Parkinsonian patients than in controls, but tyrosine levels were the same. After tyrosine lower levels of this were also found in patients compared with controls. It is suggested that these findings indicate a decreased rate of tyrosine utilization in Parkinson's disease together with intestinal malabsorption; the latter is supported by the finding of abnormal D-xylose tolerance in these patients.