Utility of FebriDx in early identification of possible COVID 19 infection

Background Reliable differentiation between uncomplicated and self-limiting acute respiratory tract infections (ARIs) and more severe bacterial respiratory tract infections remains challenging, due to the non-specific clinical manifestations in both systemic bacterial or viral infections. The current COVID-19 pandemic is putting extraordinary strain on healthcare resources. To date, molecular testing is available but has a long turnaround time and therefore cannot provide results at the point-of-care, leading to a delay in results thereby exposing patients to cross-infection and delay in diagnosis (1-3). Methods We prospectively evaluated the utility of FebriDx®, a point-of-care fingerstick blood test that can differentiate viral from bacterial ARIs through simultaneous detection of both Myxovirus-resistance protein A (MxA) and C-reactive protein (CRP), in rapidly determining viral cases requiring immediate isolation and confirmatory molecular testing, from non-infectious patients or bacterial infections that require antibacterial therapy. Results 75 consecutive patients were assessed and 48 eligible cases were tested with FebriDx®. Overall, 35 patients had FebriDx® test viral positive. All 35 patients had either positive rt-PCR (n=30) for COVID-19 or clinical picture highly suggestive of COVID-19 infection of 100% in a pandemic situation)[AB1] . In the 13 cases it was viral negative, rRT-PCR was also negative in all cases. In one case of LRTI, it was not possible to determine the exact cause of infection and a viral infection couldn’t be excluded. Including patient, the NPV was 12/13 (92%) exceeding the NPV of rRt-PCR at 71% (12/17). Sensitivity was conservatively calculated at 97% (35/36) compared to 85.7% (30[RS2] /35) for rRt-PCR. the specificity of both FebriDx®and rRt-PCR was 100% (12/12). Conclusions In the current COVID-19, FebriDx® shows potential as a reliable POC test and a proxy marker of COVID-19 infection amongst inpatients in a secondary care setting.


Background
Acute respiratory infection (ARI) is the most common reason patients seek healthcare worldwide.
Uncomplicated ARIs in the outpatient setting are often of viral origin [acute bronchitis (90%), pharyngitis (85%), and sinusitis (98%)] or are self-limiting and tend to resolve without antibiotics. 1 Reliable differentiation between uncomplicated and self-limiting ARIs and more severe bacterial respiratory tract infections remains challenging, primarily due to the non-specific overlapping clinical manifestations which can be present in both clinical scenarios, and secondly because many patients have hypersensitivity to, are carriers of, or are colonized with bacterial or viral pathogens.
The current COVID-19 pandemic is putting an extraordinary strain on healthcare resources. To date, only molecular testing is available (rRT-PCR), but has a long turnaround time and marginal sensitivity, and therefore cannot provide results at the point-of-care in suspected cases, leading to a delay in results and exposing patients to cross-infection and delay in diagnosis. 2,3 FebriDx is a 10minute, point-of-care (POC) test that uses a fingerstick blood sample to differentiate viral from bacterial ARI through simultaneous detection of both Myxovirus resistance protein A (MxA) and Creactive protein (CRP). MxA is an intracellular protein that becomes elevated in the presence of acute viral infection and CRP is an acute-phase inflammatory protein that is elevated in the presence of a systemic bacterial and/or viral infection. FebriDx may be used to triage patients with non-specific ARI symptoms in a General Practice, Hospital or ED setting, streamlining patients for confirmatory testing and facilitating hospitalisation or discharge. 4,5 We hypothesised that FebriDx could significantly decrease time to presumed diagnosis and allow for appropriate isolation from the outset, in suspected COVID-19 cases presenting to Hospital / ED. The primary objective was to determine positive predictive value (PPV) of FebriDx measured against the SARS-CoV-2 rRT-PCR on throat and nasal swabs and the clinical criteria. In addition, the sensitivity and specificity of FebriDx compared with rRT-PCR was calculated.

Study Design and Patients
We prospectively evaluated the use of FebriDx in 48 consecutive symptomatic ARI patients presenting in the Hospital / ED setting with suspected COVID-19 infection, in order to determine if it could rapidly identify and guide stratification between those requiring immediate isolation and confirmatory molecular testing, from non-infectious patients or bacterial infections that require antibacterial therapy alone. Inclusion and exclusion criterion are summarized in Figure 1.
FebriDx (Lumos Diagnostics, Sarasota, FL, USA) is a point-of-care (POC) lateral flow test that rapidly assesses the body's host immune response to an ARI and differentiates viral from bacterial infections.
FebriDx identifies host immune response to infection and differentiates viral and bacterial ARI through the simultaneous detection of both Myxovirus resistance protein A (MxA) and C-reactive protein (CRP) directly from a fingerstick blood sample. MxA is specifically induced by the production of Type I interferon (IFN) α/β. The IFN system is a key component of the innate host response to viral infections and has immune modulating and antiviral functions. 6 Type I IFNs are produced by many different cell types, specifically monocytes and macrophages, in response to a wide range viral infections and are found to be elevated in the presence of most acute viral infections 5,7,8 C-reactive protein (CRP) is a nonspecific, acute-phase protein that is upregulated due to acute inflammation, including response to infection. CRP is predominately produced by the liver in response to inflammatory cytokines such as IL-6 and assists in pathogen recognition and phagocytosis by macrophages and bacterial infection is a potent stimulus of CRP. [9][10][11][12][13][14][15][16][17] When viral pathogens induce a clinically significant host immune response, MxA, a biomarker of the body's innate response to a viral infection, will elevate. While a bacterial infection is associated with an elevated CRP in the absence of MxA. Consistent with previous studies, an elevation of MxA with or without elevation in CRP was interpreted as a viral infection; and an elevation in CRP without MxA was interpreted as a bacterial infection. FebriDx was used according to the manufacturer package insert and results were verified by two physicians.
Patients meeting the inclusion criteria were offered the POC FebriDx test at the same time as the nasal and pharyngeal swab for viral PCR testing (COVID-19, Influenza A, Influenza B and Respiratory Syncytial Virus (RSV)). They also had standard routine blood tests and procalcitonin (PCT) measured at the same time. Patients who had recent onset of symptoms and clinical course consistent with COVID-19 infection along with bilateral infiltrates / pneumonia on CXR and lymphocytopenia were categorised as very highly suspicious of COVID-19 infection. This was confirmed by two independent physicians. Others were categorised as having a low likelihood of COVID-19 infection. Any patients with both FebriDx positive and COVID-19 (rRT-PCR) negative tests, were considered clinically to have COVID-19 infection, if the clinical suspicion of COVID-19 was high (as above).

Primary endpoint
The primary endpoint of our study was the positive predictive value (PPV) of FebriDx in identifying the patients who test positive on viral swab tests or had very high clinical likelihood of COVID-19 infection. Test results were logged and tallied against the viral swab results, as well as the clinical likelihood of COVID-19 infection.

Secondary endpoint
The secondary endpoint was the negative predictive value (NPV) of FebriDx in excluding COVID-19 infection, in hospitalised patients with respiratory tract symptoms during a pandemic situation.

Statistical Analysis
The data was summarized using descriptive statistics and results are reported as medians and interquartile ranges or means and standard deviations, as appropriate. Categorical variables are summarized numerically and percentages.

Results
The study was conducted between 26 th March and 7 th April 2020. 75 consecutive patients were assessed, 26 patients excluded, 25 were due to history of symptoms being longer than 7 days in duration and 1 was immunosuppressed. 49 patients were tested with FebriDx, 48 tests were completed and 1 could not be done due to inability to obtain enough blood. Of the 48 patients In this study, the overall sensitivity of FebriDx for COVID-19 infections was 100% (97.2% for viral infection), compared to 85.7% for the rRT-PCR. The specificity of both FebriDx and rRt-PCR was 100%.
Overall diagnostic performance is summarised in Table 2.

Discussion
To our knowledge, this is the first prospective study during the SARS-CoV-2 pandemic, evaluating the utility of FebriDx in rapidly identifying, isolating and cohorting suspected cases of COVID-19 disease in a hospital / ED setting. In this study, 7 patients who in the end did not have COVID-19, were inadvertently exposed to COVID-positive patients whilst being cohorted with other suspected cases while awaiting swab rRT-PCR results (>48hours). Utilising FebriDx for enabling cohorting decisions would have avoided exposure in these cases. Similarly, 12 other patients without COVID-19 were exposed to positive study patients as a result of the similar cohorting arrangements. Avoiding mixing these patients with other suspected COVID-19 patients whilst awaiting the results of rRT-PCR, would avoid unnecessary exposure to COVID-19 positive patients.
Our study is not without limitations. Based on the urgent need for to improve testing turnaround times and isolation strategies at our hospital, it was not possible to design and perform a multicentre trial. Also, due to the need address the immediate needs to significantly more patients in the hospital, it was not feasible to increase study duration and thus cohort size. Many other hospitals in the area, and globally, are faced with similar delays in rRT-PCR test results and marginal sensitivity and therefore may also find benefit in incorporating a rapid POC testing strategy to improve isolation practices. Finally, patients presenting in our hospital with COVID symptoms were generally adults. Therefore, additional studies would be required to assess this strategy in children.
At the moment, in our clinical setting, and according to overwhelming data reports by the PHE , the centres for disease control and prevention of America and Europe (CDC and ECDC), the predominant virus causing hospitalisation amongst adults at present, seems to be SARS-CoV-2. 19 Based on our study findings, it is evident that FebriDx can be successfully deployed as a reliable triage test amongst inpatients in this pandemic situation.