RT-PCR negative COVID-19

Abstract

Background: COVID-19 is a multi-system infection with emerging evidence-based antiviral and anti-inflammatory therapies to improve disease prognosis. However, a subset of patients with COVID-19 signs and symptoms have repeatedly negative RT-PCR tests, leading to treatment hesitancy. We used comparative serology early in the COVID-19 pandemic when background seroprevalence was low to estimate the likelihood of COVID-19 infection among RT-PCR negative patients with clinical signs and/or symptoms compatible with COVID-19.

Methods: Between April and October 2020, we conducted serologic testing of patients with (i) signs and symptoms of COVID-19 who were repeatedly negative by RT-PCR ('Probables'; N = 20), (ii) signs and symptoms of COVID-19 but with a potential alternative diagnosis ('Suspects'; N = 15), (iii) no signs and symptoms of COVID-19 ('Non-suspects'; N = 43), (iv) RT-PCR confirmed COVID-19 patients (N = 40), and (v) pre-pandemic samples (N = 55).

Results: Probables had similar seropositivity and levels of IgG and IgM antibodies as propensity-score matched RT-PCR confirmed COVID-19 patients (60.0% vs 80.0% for IgG, p-value = 0.13; 50.0% vs 72.5% for IgM, p-value = 0.10), but multi-fold higher seropositivity rates than Suspects and matched Non-suspects (60.0% vs 13.3% and 11.6% for IgG; 50.0% vs 0% and 4.7% for IgM respectively; p-values < 0.01). However, Probables were half as likely to receive COVID-19 treatment than the RT-PCR confirmed COVID-19 patients with similar disease severity.

Conclusions: Findings from this study indicate a high likelihood of acute COVID-19 among RT-PCR negative with typical signs/symptoms, but a common omission of COVID-19 therapies among these patients. Clinically diagnosed COVID-19, independent of RT-PCR positivity, thus has a potential vital role in guiding treatment decisions.

Keywords: COVID-19; Diagnosis; RT-PCR; SARS-CoV-2; Suspects.

Fig. 1

Flowchart of patients and samples included in the analysis

Fig. 2

Swim plot with x-axis illustrating time since onset of symptoms in days and y-axis represents patients. The day of hospital admission represented by black crosses, RT-PCR test timeline by orange squares, disease severity at the time of antibody test by blue diamond = asymptomatic, blue circle = mild-moderate, blue triangle = hypoxic-NO ICU, blue inverse triangle = critical. The Probables (Pt 1–20, N = 20) and matched PCR-confirmed (Pt 21–60; N = 40). Sample with (red bars = Reactive) and without (green bars = Non-reactive) COVID-19 specific antibodies at any point of blood draw. Open squares indicates peak disease severity and black star indicates deceased state at end of hospitalization. A small number of patients (Pt 11, 12, 24, 59) were PCR tested for prior hospitalization as part of routine screening while few patients developed symptoms after hospitalization. Pt 7, 15 and 16 were provider referred based on meeting clinical criteria, while Pt 9 and 14 had two RT-PCR tests carried out at different times on the same day

Fig. 3

Signal to cut-off ratio of A IgG and B IgM among pre-pandemic samples collected before 2019, RT-PCR and no clinical suspicion of COVID-19 (Non suspects), RT-PCR negative with clinical signs/symptoms of COVID-19, with no potential alternate diagnosis (Probables) and with alternate diagnosis (Suspects) and matched RT-PCR confirmed for COVID-19. Boxplot indicates the interquartile range as the box and the minimum and maximum values as whiskers. Dashed line indicates cut-off values for call for reactivity. Filled circles are individuals who received COVID-19 directed therapies. Comparison between groups were by two-sided Wilcoxon signed rank test. P1 > p-value between PCR-confirmed and Probables, P2 > p-value between Probables and Suspects, P3 > p-value between Non-suspects and Probables and P4 > p-value between Pre-pandemic and Probables

Fig. 4

Neutralizing antibody response among Pre-pandemic, Non-suspects, Suspect, Probables and PCR-confirmed cohorts. Neutralization at the 1:20 dilution of plasma samples was measure of percent inhibition. The dashed line indicates percent inhibition cut-off. Comparison between groups were by two-sided Wilcoxon signed rank test. P1 > p-value between PCR-confirmed and Probables, P2 > p-value between Probables and Suspects, P3 > p-value between Non-suspects and Probables and P4 > p-value between Pre-pandemic and Probables