The Importance of Identifying Different Types of Influenza

The Importance of Identifying Different Types of Influenza

Influenza is a viral pathogen that affects millions of people every year. This infection is characterized by symptoms that include fever, cough, and chills, but clinical features can vary based on the type of pathogen causing the infection. While many influenza infections resolve spontaneously, some protracted infections can become severe, leading to hospitalizations and an increased mortality rate.

Influenza viruses pose a threat to public health when left unidentified. Medical professionals need trusted influenza diagnostics to provide specific and sensitive results in order to guide treatment and reduce transmission.

Why Is It Important to Identify Different Types of Influenza?

Influenza viruses belong to the same viral family — Orthomyxoviridae — but each genera presents with different clinical features, symptom severity, and transmission efficiency. Accurate and early diagnosis of the viral pathogen enables rapid and effective antiviral therapy that can reduce morbidities and mortalities related to seasonal epidemics and pandemics of influenza.

While symptom severity can vary between etiologies, many influenza infections present with similar clinical features in the early stages of infection. These clinical manifestations include fever, cough, headache, and body aches. Assessing symptoms alone is insufficient to identify the etiological agent and how the infection may progress. With an estimated 9 million people sick with influenza and 10,000 hospitalizations in the 2021-2022 flu season, reliable testing methods are essential for containing outbreaks.

Early diagnosis can reduce the severity of symptoms and shorten the length of illness. Reducing the duration of illness is critical to public health as it reduces the likelihood of transmission and minimizes the strain on medical staff during flu seasons.

Some populations are more at risk than others. Given that specific types of influenza present with more severe symptoms, early diagnosis can reduce mortality rates in at-risk populations. People most at risk for influenza infections include:

  • Pregnant women
  • Young children
  • Immunocompromised individuals
  • Older people

Types of Influenza Viruses

There are four known types of influenza that have distinct biological characteristics. The differences between these etiologies are essential for effective antiviral therapy and limiting transmission to at-risk groups.

Influenza A

Influenza A is the predominant etiological agent for flu infections, causing seasonal flu epidemics around the world. Influenza A has two subtype categories based on the proteins located on the surface of the viral pathogen — hemagglutinin (H) and neuraminidase (N). There are 18 known H types and 11 known N types that can influence the clinical features of infection.

Influenza A infects humans and animals and likely has more than 130 subtype combinations in nature. Many of these subtype combinations have been identified in wild birds. These subtype combinations occur when viral pathogens undergo reassortment, or swap gene segments to create a new pathogen. H1N1, commonly known for its outbreak in 2009, is an example of an influenza A subtype.

Influenza B

Influenza B only infects humans and is divided into lineages rather than subtypes — B/Yamagata and B/Victoria. An influenza B infection is typically milder than an influenza A infection and is typically not responsible for the epidemics and pandemics that type A causes. Type B often causes illness later in flu season, whereas type A causes infections earlier.

Influenza C

Influenza C is known to infect humans and pigs, though human infections are rare compared to types A and B. With the limited amount of human infections, this influenza type is not studied as frequently. It’s believed that many people are exposed to influenza C in childhood, but the exposure often does not result in infection.

Type C does not have lineages or subtypes like types A and B. With very little variation in this viral pathogen, it has a limited ability to mutate and is unlikely to cause a pandemic. In rare cases, type C has caused localized epidemics, but the infections were minor enough to prevent disruptions to public health.

Influenza D

Influenza D is not known to infect people and is most commonly found in cattle. This influenza type has a similar gene structure to type C. While it is not known to infect humans, the possibility has not been entirely ruled out, especially for people who often work with cattle.

How Is Influenza Diagnosed?

Influenza can be diagnosed through various methods.

The Importance of Identifying Different Types of Influenza

Rapid Influenza Diagnostic Tests

Rapid Influenza Diagnostic Tests (RIDTs) are antigen detection assays. These tests can detect the viral pathogens in a sample within 15 minutes and offer low to moderate sensitivity. The benefit of RIDTs is the ability to use them in an outpatient setting and see results quickly. However, many of these assays cannot distinguish between influenza A and B.

Typically, RIDTs are used for initial tests for suspected influenza infections, but tests with higher sensitivity are used to confirm. The likelihood of false negatives with RIDTs is also high, so they are not an ideal standalone diagnostic tool.

Viral Culture

This laboratory technique involves taking a sample of tissue or fluid and adding it to a collection of cells to see if the viral pathogen grows. If a virus does not infect the cells, the culture is negative. This process takes time and observation to allow for pathogen growth and identify the type and subtype. Viral cultures are a valuable process for identifying mutations and altering influenza vaccinations for the next year.


Immunofluorescence is a type of antigen detection assay that uses a fluorescent microscope to identify influenza pathogens in a sample. The process takes between two to four hours and offers

moderate sensitivity with high specificity. These assays can use direct or indirect fluorescent light and can distinguish between influenza A and B.

Rapid Molecular Assays

Rapid molecular assays detect and amplify viral RNA in a sample to identify the presence of a pathogen. These tests offer high sensitivity and high specificity and can discriminate between types A and B. Some molecular assays can also distinguish between the subtypes of influenza A. Processing time for these assays varies by product but can take one hour to eight hours.

The Importance of Identifying Different Types of Influenza

Choose Influenza Diagnostics From Applied BioCode Inc.

The BioCode® CoV-2 Flu Plus Assay detects and differentiates four pathogens in a single sample — SARS-CoV-2, Influenza A, Influenza B, and Respiratory Syncytial Virus (RSV), and has been authorized for emergency use by the FDA under Emergency Use Authorization (EUA). As a multiplexed nucleic acid test, the CoV-2 Flu Plus Assay provides qualitative detection and differentiation of the RNA from each pathogen. This assay uses samples from nasopharyngeal swabs.

Boost clinical efficiency and diagnostic accuracy with our assay and our system. The CoV-2 Flu Plus Assay runs with the BioCode® MDx-3000 that can process up to 96 samples and three different panels simultaneously. Medical professionals can also run the CoV-2 Flu Plus Assay alongside the Applied BioCode® Respiratory Pathogen Panel to detect and rule out pathogens with overlapping clinical features.

Contact us today for more information about our assays.