Flu, RSV or COVID-19? Why the Answer Matters More Than Ever

The Triple Threat: Influenza (Flu), RSV and SARS-CoV-2

Every respiratory season, three viruses converge on clinics and emergency rooms, producing an almost identical picture: fever, cough, sore throat, congestion and fatigue but underneath that one label, sits three distinct pathogens with different risk profiles and treatment pathways.

Influenza A and B are highly contagious RNA viruses behind seasonal epidemics; Influenza A subtypes such as H1N1 and H3N2 tend to cause the most severe outbreaks. Respiratory Syncytial Virus (RSV) is a leading cause of lower respiratory tract infection in infants, the elderly and the immunocompromised, peaking in winter months. SARS-CoV-2, now an endemic respiratory pathogen, continues to evolve into new variants that periodically reshape transmissibility and severity.

These viruses are treated and managed differently. Knowing the correct virus helps doctors to select the appropriate treatment, assess the risk to a patient, make decisions about isolation, if necessary and identify cases in which more than one virus is causing the infection during peak respiratory season.
According to The World Health Organization (WHO), influenza, RSV and COVID-19 are still major causes of acute respiratory infections globally with seasonal co-circulation adding to the burden on health systems.

Influenza (Flu)¹

          ·   Annual cases: Approximately 1 billion seasonal influenza infections worldwide.

          ·   Severe cases: 3–5 million cases of severe illness each year.

          ·   Deaths: About 290,000–650,000 respiratory deaths annually. 

RSV (Respiratory Syncytial Virus)²

          ·   Hospitalizations (children <5 years): Around 3.6 million RSV-associated hospitalizations every year.

          ·   Deaths (children <5 years): Approximately 100,000 deaths annually.

          ·   97% of paediatric RSV deaths occur in low- and middle-income countries.

Diagnosis: Why Molecular Testing Leads

Respiratory virus diagnostics generally fall into antigen-based rapid tests, viral cultures and nucleic acid amplification tests (NAATs). Nucleic acid amplification tests such as RT-qPCR (Molecular Testing) offers far greater analytical sensitivity, often detecting infection at viral loads of magnitude lower than antigen tests. This is important early in illness and in patients with weaker viral loads. A built-in internal control also verifies the sample itself was adequate and properly processed.

Because these three viruses overlap so closely in symptoms, testing for just one at a time leaves a real gap. Syndromic, multiplex panels solve this by detecting several relevant pathogens from a single specimen in a single run: one extraction answers “which virus does this patient have,” not just “does this patient have flu.” That completeness also supports better antiviral and antibiotic stewardship and gives laboratories sharper, real-time visibility into which viruses are actually circulating.

Prevention: Reducing the Burden Before It Starts

A layered prevention strategy remains the most effective defence, especially for infants, older adults, pregnant individuals and the immunocompromised. Annual influenza vaccines, RSV vaccines and updated COVID-19 boosters meaningfully cut the risk of severe illness and hospitalisation.

Everyday measures still matter just as much: regular hand hygiene, covering coughs and sneezes, using masks when symptomatic, good indoor ventilation, routine surface cleaning and simply staying home while unwell. For high-risk groups, the combination of timely vaccination and prompt testing at first symptoms are important.

A Validated Molecular Solution: TRUPCR ® Influenza A/B and RSV with SARS-CoV-2 RT qPCR Kit

The TRUPCR® Influenza A/B and RSV with SARS-CoV-2 RT qPCR Kit is a multiplex real-time PCR assay designed for the qualitative detection of multiple clinically important respiratory viruses from a wide range of respiratory specimens, including nasopharyngeal swabs and nasal aspirates. It is intended to detect:

          ·   Influenza A

          ·   Influenza B

          ·   Pandemic H1N1 Influenza virus

          ·   H3N2 Influenza virus

          ·   Human Respiratory Syncytial Virus (HRSV)

          ·   Sarbecovirus (E gene)

          ·   SARS-CoV-2 (N + RdRp gene)    

This assay incorporates human RNaseP as an internal control to assess specimen quality and support result reliability.
The kit has shown good analytical and clinical performance:

Analytical Sensitivity (Detection Limit)

          ·   Influenza A, Influenza B, RSV, H1N1 and H3N2: 1 copies/µL

          ·   Sarbecovirus and SARS-CoV-2: 6 copies/µL 

 
Clinical correlation study
In a study of 364 clinical samples for Influenza A/B, RSV, H1N1 and H3N2, the kit demonstrated:

          ·   Influenza A sensitivity 98.10%

          ·   RSV sensitivity: 98.15% 

          ·   Sensitivity (H1N1): 98.11%

          ·   H3N2 Sensitivity: 98.25 %

          ·   Influenza B test sensitivity: 98.00%

          ·   Specificity: 100% 

In another study of 60 samples for the detection of SARS-CoV-2, the kit gave:

          ·   Sensitivity 100%

          ·   Specificity: 100 %

Conclusion

Influenza, RSV and SARS-CoV-2 remain a significant burden on healthcare systems due to their high transmissibility, overlapping symptoms and risk of severe complications. In such a landscape, fast and reliable molecular diagnostics are not optional, they are essential. Syndromic RT-PCR panels offer a convenient, clinically relevant approach for rapid and accurate detection of multiple respiratory viruses from a single specimen.

The TRUPCR® Influenza A/B and RSV with SARS-CoV-2 RT qPCR Kit fulfils this need, providing broad respiratory virus coverage, robust analytical sensitivity, high specificity and validated clinical performance.

Publications

1. Shamsundar R, Mathew R, Joy S, et al. Overview of Diagnostic Testing for Viral Respiratory
    Tract Infections in India. J Acad Clin Microbiol  2025;27(2):44–57.

    https://www.jacmjournal.org/doi/pdf/10.5005/jacm-11020-0028

2. Khan T, Halder S, Das RS, Jaiswal A, Leo PHS, Mahato A, Ghosh T, Satpathi P and Bhattacharya
    SD (2025) Molecular epidemiology of influenza,respiratory syncytial virus, SARS-CoV-2, other
    respiratory viruses and bacteria among children 0–2-year-olds in West Bengal: a one-year
    influenza-like illness surveillance study (2022–2023). Front. Epidemiol. 5:1578951. doi:
    10.3389/fepid.2025.1578951

    https://www.frontiersin.org/journals/epidemiology/articles/10.3389/fepid.2025.1578951/full

Data Sources

1. https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)

2. https://www.who.int/news-room/fact-sheets/detail/respiratory-syncytial-virus-(rsv)