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H3N2 Influenza: Most effective techniques to diagnose it; know if you are at risk

By, New Delhi
Mar 20, 2023 01:29 PM IST

H3N2 Influenza hospitalisations are on rise in India; children and elderly could be most at risk. Know the risk factors and the best ways to diagnose it.

H3N2 Influenza virus has been increasing the number of hospitalisation cases in Delhi and surrounding areas and while most cases out of the 1000 detected in the country have been mild, government advisory has warned people to take precautions like cleanliness, preventing crowding, and hand hygiene. Children below 6 years and adults above 65 years have been asked to take special precautions as they are among the vulnerable group. (Also read: H3N2 Influenza: Signs and symptoms of severe illness to watch out for)

All viral respiratory illnesses be it influenza A- H3N2, H1N1 variant, novel coronavirus 19, and omicron sub variant, are steadily increasing, because of host of environmental factors (REPRESENTATIVE IMAGE)

Respiratory diseases may be on rise this spring due to a host of factors from pollution, festive gatherings, lack of hand hygiene, and lowered immunity among others. It is important to distinguish H3N2 influenza symptoms from those of Covid as while the latter is said to last for 2-3 days and the patient recovers soon, H3N2 and H1N1 can stretch for a couple of weeks and may even has more chances of leading to pneumonia or a secondary bacterial infection, say experts.

"Currently approximately 30 per cent of patients visit with symptoms of upper or lower respiratory issues. Symptoms are more or less the same for any viral illness- sore throat, dry cough, headache, myalgia, diarrhoea, only difference is that in the present clinical scenario, Covid symptoms barely last for 2-3 days and the patient recovers soon without any hassles and any major treatment. Whereas with H3N2 and H1N1 has more predilection for productive and wet coughs which lasts longer for a few weeks and has more chances of getting pneumonia or a secondary bacterial infection. Irrespective of the virus if there is a major comorbid factor there are more chances of morbidity and mortality,"

Dr Samrat Shah, Senior Consultant, Internal Medicine, Sir HN Reliance Foundation Hospital told HT Digital.

Elaborating on the causes of rise in respiratory infections, Dr Shah said, "in the current scenario, all viral respiratory illnesses be it influenza A- H3N2, H1N1 variant, novel coronavirus 19, and omicron sub variant, these are steadily increasing, because of host of environmental factors. Some of the host factors are avoidance of face masks, casual attitude towards general health, lack of hand hygiene, and more social gatherings. Some of the environmental factors contributing to the increase in cases are poor air quality and excessive construction pollution. The only way to prevent this influenza virus complication is by vaccinating once a year with the quadrivalent flu vaccine."

Why there is surge of Influenza infections and hospitalisations in India

"India is currently seeing a surge in influenza viral infections due to H3N2. Influenza A viruses infect humans and many different animals. The emergence of a new and very different influenza A virus with the ability to infect people and have sustained human to human transmission, can cause an influenza pandemic and therefore is of most significance to public health," says Dr Sunita Kapoor, Director and Consultant Pathologist at City X-ray & Scan Clinic.

"Influenza type A viruses are classified into subtypes according to the combinations of different virus surface proteins, hemagglutinin (HA) and neuraminidase (NA). Current subtypes of influenza A viruses that routinely circulate in people include A(H1N1) and A(H3N2). In years in which H3N2 is the predominant strain, there are more hospitalisations. Human infections are primarily acquired through direct contact with infected animals or contaminated environments, these viruses have not acquired the ability of sustained transmission among humans," adds Dr Kapoor.

Who is at risk from H3N2 influenza virus

Dr Kapoor says small children and elderly are among those who are most at risk of this virus while pregnant women, those with weakened immune system, chronic illnesses and travellers might be at risk of this virus too.

Here are those who are at risk of H3N2 influenza virus:

- Young children under age 2

- Adults older than age 65

- Residents of nursing homes and other long-term care facilities

- People who are pregnant or plan to be pregnant during flu season

- People with weakened immune systems

- People who have chronic illnesses, such as asthma, heart disease, kidney disease, liver disease and diabetes

- Health care workers performing aerosol generating procedures.

- Travelers to countries and people living in countries with known outbreaks of avian influenza

Diagnosis of H3N2 virus

Dr Kapoor says influenza virus detection techniques have been classified into four categories:

- Traditional methods, e.g., viral culture serological methods, e.g., immunofluorescence assays, complement fixation, immunodiffusion test, virus neutralization method, hemagglutination method, rapid antigen testing.

- Advanced quick methods which include NAT (Nucleic acid tests) like RT PCR, multiplex PCR, nucleic acid sequence-based amplification (NASBA), and conventional PCR.

- Bio-sensing methods which include includes optical biosensors, giant magneto-resistance biosensors, aptamer-based biosensors, and electrochemical biosensors

Nucleic acid-based tests

"Nucleic acid tests (NAT) employ PCR and virus-specific RNA or DNA sequences/genetic material instead of viral antibodies or antigens. These are much more susceptible and specific as compared to serological assays and can diagnose viruses in many earlier clinical samples. An antibody-based test takes time because the human body cannot make antibodies instantly at a detectable level. Therefore, NAT can overcome this limitation of serological methods. Most of these methods take 2–4 hours to complete the detection," says Dr Kapoor.


This technique is considered the most powerful tool for the detection of the influenza virus. Nested primers are utilised to detect and subtype influenza viruses. The results of this test present extremely high sensitivity and specificity, the greatest of all traditional detecting approaches.

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