Diagnosing Influenza at the Point of Care

Influenza, or ‘flu’, is a common respiratory infection usually associated with a seasonal increase during the winter months – often referred to as ‘flu season’.

There are estimated to be around 1 billion cases annually, with more severe symptoms for those at higher risks, such as those with weakened immune systems.

This short post explores how diagnosis of influenza at the point-of-care can make a difference to patients and healthcare services.

What are Influenza Viruses?

Influenza viruses are zoonotic viruses, which means they can infect animals and birds, as well as humans.

Of the four Influenza viruses, A, B, C and D, Influenza virus A and Influenza virus B are associated with ‘seasonal’ influenza, causing infections in humans during the winter months. Influenza C causes mild respiratory disease but not widespread infection, and Influenza D is primarily a disease of cattle (ref: CDC).

What is Influenza A?

Influenza A, the influenza virus with a history of being the cause of pandemics, is classified into different subtypes according to two surface proteins, haemagglutinin (H) and neuraminidase (N). There are 18 different H subtypes; eight of which have been detected in humans (H1, H2, H3, H5, H6, H7, H9, H10), and six N subtypes (N1, N2, N6, N7, N8, and N9) which have been detected in humans. So far, more than 130 different subtypes of influenza A have been identified (ref: CDC).

What is Influenza B?

In comparison, Influenza Virus B is classified into two lineages: B/Yamagata and B/Victoria (ref: CDC pink book) and Influenza viruses C and D don’t have H or N surface proteins, only a single hemagglutinin-esterase-fusion protein (ref: Wolff & Veit, 2021).

In the popular press, strains of influenza are often given colloquial names, such as bird/avian flu or swine flu, according to the animal host in which the influenza virus emerges and/or spreads.

Officially, Influenza viruses are named in a particular way made up of the following pieces of information:

Influenza virus/animal origin/geographical origin/strain/year of origin/haemagglutinin type neuraminidase type

For example:

A/Muscovy duck/England/074477/2021/H5N1

Impact of Influenza on healthcare services

Most cases of influenza in otherwise healthy individuals are likely to be self-limiting with symptoms that can be managed at home; however, every year influenza (and other respiratory viruses) has a significant impact on healthcare services.

During the 2022/23 winter season, there were 49,300 confirmed influenza cases admitted to hospital in England (ref: Lancet). Diagnosis becomes particularly important for those in at risk groups who are vulnerable to serious influenza infection and are more likely to require healthcare intervention and/or hospitalisation.

Improving Influenza care with Point of Care diagnostic testing

Reduce unnecessary hospital admissions

A key initiative of the NHS Urgent and Emergency Care Recover Plan is the implementation of Acute Respiratory Hubs within the community. These services provide “urgent same-day face-to-face assessment for acute respiratory infections, help to speed up access to care and advice while reducing wider system pressures and unnecessary hospital admissions”, they also “make better use of existing capacity by improving patient flow”.

NHS Urgent and Emergency Care Recover Plan

Implementation of appropriate point-of-care tests for diagnosis of respiratory infections, including influenza, in these community hubs will provide healthcare professionals with the information they need to make an informed clinical decision about the best care/management for a patient.

Point-of-care testing offers rapid triage

Many patients with influenza-like illness (such as fever, cough, sore throat, muscle aches, fatigue) present to emergency and acute hospital settings. Application of rapid and accurate triage in these locations can help alleviate pressure on existing services by improving patient flow.

The use of rapid, multiplex PCR testing for respiratory viruses placed directly in emergency and acute settings has been associated with a significant reduction in time to results compared with routine laboratory testing (−24.22 h, 95% CI −28.70 to −19.74 h) (Clark et al., 2023).

Read more: The Clinical Impact of Rapid Multiplex PCR Testing For Respiratory Viruses

The availability of a rapid result indicating a diagnosis of influenza in busy clinical environment means that not only can a healthcare professional make an informed decision about the best treatment plan for the individual patient, but timely infection prevention and control interventions for influenza-positive patients can be taken to protect others in the area from acquiring the infection.

When patients were tested for influenza with a molecular point-of-care test, 70% (70/100) were isolated to single-room accommodation compared with much fewer patients that received routine clinical care (38%, 39/102) (relative risk 1·8 [95% CI 1·4–2·4; p<0·0001]) (Clark et al., 2021).

Appropriate antiviral treatment

For those patients that need them, antivirals, such as oseltamivir or zanamivir, are available to treat influenza. Most effective when given early in the course of infection, antiviral medication can reduce the severity of symptoms, the duration of illness and is crucial for the management of those at risk of serious infection or complications of influenza.

In one randomised controlled trial in England, patients who received a molecular point-of-care test (mPOCT) for influenza were more likely to be given antiviral treatment within five days of admission (99/100, 99%) compared with the standard of care group (63/102, 62%, <0.0001). Based on these findings and the clinical outcome of patients, the authors made the following recommendation:

“Routine mPOCT should replace laboratory-based diagnostics for acute admissions to hospital during the influenza season.” Clark et al., 2021

Confident decision making at the point-of-care

Influenza activity is closely monitored worldwide. The northern hemisphere looks to the southern hemisphere (and vice versa) to predict the intensity and severity of influenza activity in an upcoming winter season. For instance, in 2023 Australia has seen a significant increase in the amount of influenza B circulating in the community, with a large number of cases identified in young children (ref: Guardian).

A point-of-care test for influenza needs to be able to differentiate reliably between influenza A and B viruses, detect strains that are expected to be circulating and include coverage of strains that would be of concern should they emerge and cause widespread infection, such as a highly pathogenic avian influenza H5N1 virus.

One advantage of molecular point-of-care tests for influenza is that the sequences used for primers and probes within an assay can be checked regularly against genetic sequences of all influenza viruses without the need for laborious testing in a laboratory. Using the GISAID database, sequences can be checked using a computer, giving confidence that an assay is up-to-date and has the capability to detect any known influenza strain.

Ideally, a point-of-care test for influenza would simultaneously differentiate between other respiratory viruses that cause similar symptoms and have the potential to cause serious infection in vulnerable groups, without the need to run multiple tests.

The QuantuMDx point-of-care influenza testing device

The Q-POC™ SARS-CoV-2, Flu A/B & RSV Assay is a rapid, sample-to-result multiplex PCR test designed to be run on the Q-POC™ platform at the point of care.

The Q-POC SARS-CoV-2, Flu A/B & RSV Assay provides simultaneous and accurate diagnosis, triage and management of these clinically similar respiratory infections within 35 minutes. The compact and robust platform is ideal for use in busy clinical settings, and the single use, self-contained cassette ensures safe testing.

Get in touch to find out how to implement the Q-POC SARS-CoV-2, Flu A/B & RSV Assay and diagnose influenza at the point of care in your clinical practice.