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Point-of-care test helps distinguish bacterial and viral causes of acute respiratory infections

A point-of-care test shows good sensitivity for identifying either bacterial or viral pathogens in patients with acute respiratory infections

A point-of-care test based on the host’s immune response, has been found to correctly distinguish between bacterial and viral infections in patients with acute respiratory infections according to the results of a diagnostic study by team of US researchers.

Respiratory symptoms are the motive for a third of emergency room visits by both adult and paediatric patients. Acute respiratory infections such as acute bronchitis, sinusitis, pneumonia and the common cold will often present with overlapping symptoms leading to over-prescribing of antibiotics. Although multiplex PCR systems are available for the identification of bacterial and viral pathogens, an alternative strategy is to use a point-of-care test based on the host’s immune response to myxovirus resistance protein A (MxA) and C-reactive protein (CRP) in a finger-stick whole blood sample. To test the value of this approach in helping clinicians to decide on whether or not to prescribed antibiotics, in the present study, the US team examined the ability of the FebriDx® which is a rapid, point-of-care diagnostic test that is designed to aid in the differentiation of bacterial and viral acute respiratory infections. The test can provide a result within 10 minutes by identifying myxovirus resistance protein A, which is induced by type 1 interferon due to viral infections and CRP, a non-specific acute-phase protein produced in response to inflammation and infection. While CRP is not specific for bacterial infections, if only MxA levels are elevated (i.e., no change in CRP) this is indicative of a viral infection. Similarly, elevated CRP in the absence of MxA, indicates a bacterial infection.

The US team recruited patients from emergency departments and outpatient settings who presented with new-onset respiratory symptoms including rhinorrhoea, nasal congestion, sore, throat, hoarseness, cough or shortness of breath and a recent fever and an asymptomatic control group. The point-of-care test was administered to both groups of patients although the treating physicians were blind to the test results. The primary outcome was set as a bacterial or viral-associated systemic host response. In addition, patient samples were collected and analysed by multiplex PCR for either viral or bacterial identification and which served as independent assessment of the point-of-care test result.

Point-of-care test and bacterial or viral identification

A total of 520 symptomatic patients with a mean age of 35.3 (44.2% male) were included and 170 in the asymptomatic group.

Final diagnostic information was available for 496 individuals and of whom, 14.7% had a confirmed bacterial and 59.7% a viral infection with the remainder classed as negative. The point-of-care test correctly identified 93.1% of bacterial infections giving a sensitivity of 93.2% (95% CI 84.9 – 97%), a specificity of 88.4% (95% CI 85 – 91.1%) and a positive predictive value of 58.1%.

For viral infections, the point-of-care test had a sensitivity of 70.3% (95% CI 64.8 – 75.2%), a specificity of 88% (95% CI 82.8 – 91.8%) and a positive predictive value of 89.7%. Interestingly, none of the participants had a co-infection which was defined as both a bacterial and viral pathogen plus a host response based on the independent assessment.

The authors concluded that the rapid diagnostic point-of-care test could help inform clinicians when assessing for either bacterial or viral causes for acute respiratory infections.

Shapiro NI et al. Diagnostic Accuracy of a Bacterial and Viral Biomarker Point-of-Care Test in the Outpatient Setting JAMA Netw Open 2022

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