Preface

Influenza is a seasonal respiratory illness that occurs annually, usually peaking in winter. It affects 5-10% of adults and 20-30% of children each year.[1] This common, yet serious, infectious disease, represente a significant threat to public health. Globally, annual influenza epidemics are estimated to result in about 3 to 5 million cases of severe illness, millions of hospitalizations and up to 650,000 deaths every year.[2]

The Pathogen

There are 4 types of seasonal influenza viruses, types A, B, C and D. Influenza A and B viruses circulate and cause seasonal epidemics of disease.

1. Influenza A viruses are further classified into subtypes according to the combinations of the hemagglutinin (HA) and the neuraminidase (NA), the proteins on the surface of the virus. Currently circulating in humans are subtype A (H1N1) and A (H3N2) influenza viruses.
2. Influenza B viruses are not classified into subtypes, but can be broken down into lineages. Currently circulating influenza type B viruses belong to either B/Yamagata or B/Victoria lineage.
3. Influenza C viruses are detected less frequently and usually causes mild infections, thus does not present public health importance.
4. Influenza D viruses primarily affect cattle and are not known to infect or cause illness in people.

Epidemiology

All age groups can be affected but there are groups that are more at risk than others.

In terms of transmission, influenza spreads easily with rapid transmission in crowded areas. When an infected person coughs or sneezes, droplets containing viruses (infectious droplets) are dispersed into the air and can spread up to one meter, and infect persons in close proximity who breathe these droplets in. The virus can also be spread by hands contaminated with influenza viruses. To prevent transmission, people should cover their mouth and nose with a tissue when coughing, and wash their hands regularly. [2]

Signs and Symptoms

Influenza is characterized by sudden onset of symptoms [5], including a sudden onset of fever, cough (usually dry), headache, muscle and joint pain, severe malaise (feeling unwell), sore throat and a runny nose. The cough can be severe and can last 2 or more weeks. Most people recover from fever and other symptoms within a week without requiring medical attention. But influenza can cause severe illness or death especially in people at high risk as mentioned above. [2] 

Give a Timely and Accurate Flu Diagnosis

The majority of cases of human influenza are clinically diagnosed. However, during periods of COVID-19 pandemic, and other epidemics situations, e.g. rhinovirus, respiratory syncytial virus and adenovirus can also present as Influenza-like Illness (ILI) which makes the clinical differentiation of influenza from other pathogens difficult. [2]

Collection of appropriate respiratory samples and the application of a laboratory diagnostic test is required to establish a definitive diagnosis. 

Getein One Step Test for FluA/FluB/SARS-CoV-2 Antigen (Colloidal Gold) is a combo test for COVID-19 and influenza, enabling healthcare providers to rapidly and effectively differentiate between the SARS-CoV-2 and influenza A/B viruses, make informed treatment decisions and improve patient outcomes.

References

[1] WHO (2012). World Health Organization. Vaccines against influenza. WHO position paper. Weekly Epidemiol Record. 87(47):461–76.

[2] World Health Organization. Influenza (seasonal). [Internet; cited 2020 November]. 

[3] Estimates of US influenza-associated deaths made using four different methods.Thompson WW, Weintraub E, Dhankhar P, Cheng OY, Brammer L, Meltzer MI, et al. Influenza Other Respi Viruses. 2009;3:37-49

[4] Global burden of respiratory infections due to seasonal influenza in young children: a systematic review and meta-analysis.Nair H, Abdullah Brooks W, Katz M et al. Lancet 2011; 378: 1917–3

[5] Mayo Clinic (2016), Symptoms and causes. Available at http://www.mayoclinic.org/diseases-conditions/flu/symptoms-causes/dxc-20248062 last access 03 May 2021