The circulation of respiratory illnesses like the flu, COVID-19 (caused by SARS-CoV-2), and Respiratory Syncytial Virus (RSV) often overlaps, particularly during colder months. Because these viruses cause similar symptoms, people often wonder if a COVID-19 test might mistakenly turn positive due to an RSV infection. Modern diagnostic tools are highly specific to target the unique signature of SARS-CoV-2, making cross-reactivity from RSV exceedingly unlikely.
How COVID-19 Diagnostic Tests Work
The two primary types of COVID-19 tests available are designed to find specific molecular components of the SARS-CoV-2 virus. Nucleic Acid Amplification Tests (NAATs), commonly known as PCR tests, look for the virus’s genetic material (RNA). PCR uses reverse transcription-polymerase chain reaction (RT-PCR) to convert the viral RNA into DNA and then amplify it millions of times for detection, offering high sensitivity and specificity.
Antigen tests, which are the rapid, at-home tests, detect specific surface proteins from the virus, typically the nucleocapsid protein. These tests use antibodies within the test strip that are custom-made to bind only to the SARS-CoV-2 proteins. When viral proteins are present, they are captured by these antibodies, resulting in the visible line that indicates a positive result. While antigen tests are generally less sensitive than PCR, they maintain a very high degree of specificity for the SARS-CoV-2 protein targets.
Test Specificity and Viral Cross-Reactivity
The answer to whether RSV can cause a positive COVID-19 test is no, due to the high specificity engineered into authorized tests. Specificity refers to a test’s ability to correctly identify a negative sample, meaning it will not react to a substance other than the target virus. Both PCR and antigen tests use a “lock-and-key” mechanism, where the test component is specifically shaped to recognize only the unique genetic sequence or protein belonging to SARS-CoV-2.
RSV is a type of pneumovirus, which is genetically and structurally distinct from SARS-CoV-2, a coronavirus. The genetic material and surface proteins of RSV are sufficiently different that the COVID-19 test’s primers (for PCR) or antibodies (for antigen tests) will not bind to the RSV components. Analytical specificity for most authorized COVID-19 PCR tests approaches 100%, meaning they do not cross-react with other common respiratory viruses. Antigen tests generally maintain a specificity of 98% to 99%, making false positives from other viruses rare.
Symptoms and Next Steps After a Positive Result
The reason this question arises is the significant overlap in symptoms between RSV, COVID-19, and influenza. All three can cause fever, cough, runny nose, and respiratory distress, making it impossible to determine the cause based on symptoms alone. If a person tests positive for COVID-19, the result is considered accurate and indicates a SARS-CoV-2 infection, not a mistake caused by an RSV infection.
A person may be co-infected with both viruses simultaneously, which is common during respiratory season. Co-infections can lead to more severe symptoms, complicating the clinical picture. If there is suspicion of a different virus, a healthcare provider can order a multiplex PCR test. This single test simultaneously detects and differentiates between SARS-CoV-2, influenza A/B, and RSV from one sample. This definitive testing allows for the correct diagnosis and initiation of appropriate, virus-specific treatments.