What is the accuracy of the FebriDx (fever diagnostic test) in diagnosing acute respiratory infections?

FebriDx Accuracy for Acute Respiratory Infections

FebriDx demonstrates high diagnostic accuracy for differentiating bacterial from viral acute respiratory infections, with sensitivity of 80-95% for bacterial detection and 87% for viral detection, and notably high negative predictive values of 97-99% for ruling out bacterial infection. 1, 2, 3

Test Performance Characteristics

Bacterial Infection Detection

• Sensitivity ranges from 80-95% depending on whether fever is confirmed at time of testing, with higher sensitivity (95%) when hyperthermia is documented at enrollment 2, 3
• Specificity is consistently 93-94% across multiple studies in emergency department and urgent care settings 2, 4
• Negative predictive value of 97-99% makes it particularly useful for ruling out bacterial infection and avoiding unnecessary antibiotics 2, 4, 3
• Positive predictive value of 63-76% indicates moderate ability to confirm bacterial infection 2, 3

Viral Infection Detection

• Sensitivity of 87% for detecting acute pathogenic viral infection 3
• Specificity of 83-94% for identifying viral etiology 4, 3
• Negative predictive value of 95% for ruling out viral infection 3
• High NPV maintained across multiple respiratory viruses: 97.5% for influenza, 97.1% for SARS-CoV-2, and 98.1% for RSV in the context of co-circulation 5

Clinical Context and Validation

Study Populations

• FebriDx has been validated in prospective, multicenter studies involving adults and children over 2 years old presenting with acute upper respiratory tract infections 1, 2, 3
• Testing performed in emergency departments and urgent care settings where rapid decision-making about antibiotic prescribing is critical 2, 4
• 244 patients in ED study showed 87% sensitivity for bacterial infection with 91% NPV 4
• 220 patients in urgent care study demonstrated 95% sensitivity and 94% specificity when fever was confirmed at enrollment 2

Reference Standards Used

• Studies used comprehensive reference algorithms including bacterial culture, respiratory PCR panels for viral and atypical pathogens, procalcitonin, and white blood cell counts 2, 3
• Clinical adjudication by expert panels served as the gold standard in some studies 4
• This rigorous approach strengthens confidence in the reported accuracy metrics 2, 3

Practical Clinical Utility

Antibiotic Stewardship

• FebriDx results can guide antibiotic prescribing decisions by rapidly identifying clinically significant bacterial infections that warrant treatment 1, 2
• The high NPV (97-99%) for bacterial infection allows clinicians to confidently withhold antibiotics in negative cases, reducing unnecessary prescriptions 2, 4
• This aligns with NICE guidance emphasizing point-of-care testing to inform antibiotic decisions when uncertainty exists about bacterial etiology 6

Test Characteristics

• Results available in approximately 10 minutes from fingerstick blood sample 1, 3
• No additional equipment required beyond the disposable test device 1
• Simultaneous measurement of CRP and MxA provides information about both bacterial and viral immune responses 1, 2

Important Caveats and Limitations

Clinical Context Matters

• Accuracy is highest when fever is documented at time of testing (95% sensitivity vs 80% when relying on reported fever within 72 hours) 2, 3
• Positive predictive value of 63-76% means that positive results should still be interpreted in clinical context, as false positives occur 2, 3
• NICE guidelines emphasize that viral testing alone should not guide antibiotic decisions due to possibility of bacterial co-infection 6

Population Considerations

• FebriDx is indicated for patients over 2 years old with community-acquired acute respiratory infections 1
• Performance maintained during periods of multiple respiratory virus co-circulation including influenza, SARS-CoV-2, and RSV 5
• Accuracy retained in era of COVID-19 vaccination, with NPV of 97.1% for SARS-CoV-2 5

Integration with Clinical Assessment

• FebriDx should complement, not replace, clinical judgment in assessing severity and need for treatment 6
• CRP thresholds of 20 and 100 mg/L remain useful for supporting prescribing decisions in pneumonia, as recommended by NICE 6
• Face-to-face assessment remains preferable when patients are potentially ill enough to require antimicrobials 6

Comparison to Alternative Approaches

Advantages Over Clinical Diagnosis Alone

• Clinical diagnosis of bacterial vs viral infection has poor specificity without objective testing 6
• FebriDx provides objective biomarker data within minutes, unlike culture results that take days 1, 3
• Higher accuracy than clinical scoring systems like CPIS, which have sensitivity of only 72-77% 6

Role Alongside Other Testing

• FebriDx complements rather than replaces PCR testing for specific pathogen identification 6
• Can be used as triage tool to identify patients who need further investigation versus those who can be managed conservatively 5
• Particularly valuable in outpatient settings where rapid decisions about antibiotic prescribing are needed 1, 2