Positive antigen test provides reliable information on the cause of severe upper respiratory infections

Upper respiratory infections, such as the common cold and flu, are highly prevalent and spread easily, often through coughing or sneezing. These infections are most commonly caused by viruses that inflame the respiratory tract mucous membranes, resulting in symptoms like a runny nose, sore throat, and cough.

Accurate and rapid diagnosis of upper respiratory infections is crucial for timely and effective treatment, as well as for controlling transmission. Quick diagnosis also helps avoid unnecessary antibiotic use, which is ineffective against viruses and contributes to antibiotic resistance.

Diagnosing upper respiratory infections in clinical laboratories presents challenges. Physicians require laboratory results quickly, and testing methods need to be sensitive, accurate, and cost-effective. In diagnosing viral infections, traditional viral culture is effective but slow, labor-intensive, and costly. As a result, modern diagnostic methods prefer PCR tests, which detect viral genetic material (nucleic acids), or antigen tests, which detect viral protein components.

Researchers from the University of Oulu, the Wellbeing Services County of Lapland, and NordLab compared two antigen tests used in upper respiratory infection diagnosis with the PCR method. Both antigen and PCR tests detect four significant upper respiratory viruses: influenza A, influenza B, respiratory syncytial virus (RSV), and SARS-CoV-2. The study was conducted at the emergency departments of Lapland Central Hospital and Länsi-Pohja Central Hospital between 2023 and 2024.

The research confirmed that the PCR method was notably more sensitive than antigen testing. However, the antigen test proved highly accurate, with a positive result reliably identifying the infection’s cause. According to the study, PCR sensitivity can sometimes complicate diagnosis, as the test may return positive results for traces of past infections, leading to potential interpretation issues.

“Based on the study, if a patient with pronounced upper respiratory symptoms tests negative with an antigen test, it is advisable to conduct a PCR test. However, if the antigen test is positive, the result is generally reliable. This is particularly relevant during peak times in emergency departments,” summarises Ilkka Junttila, Professor of Clinical Microbiology at the University of Oulu and Chief Medical officer of Clinical Microbiology at NordLab.

The study was published in Microbiology Spectrum on November 26: Savolainen LE, Peltola J, Hilla R, Åman T, Broas M, Junttila IS. 0. Clinical performance of two commercially available rapid antigen tests for influenza, RSV, and SARS-CoV-2 diagnostics. Microbiol Spectr 0:e01630-24.