Health and Tech: Influenza is now twice-a-year affair

In recent years, this once-a-year event has transformed into a twice-a-year occurrence, as epidemiologists and public health experts acknowledge the emergence of two seasonal peaks for influenza cases.

Upper respiratory tract infections, especially influenza, are usually associated with drop in temperature during winter. As temperature dips, the circulatory virus, which is active locally, finds congenial conditions to proliferate and infect people. In the last few years, however, this once-in-a-year affair has become a twice-in-a-year affair, as epidemiologists and public health experts have realised that cases of influenza now have two peaks in a year.

These days, cases of influenza rise during the monsoon (July to September) and the winter season from December to February. Chances of a surge in influenza cases increase in regions that experience active monsoons, a vital reason why vulnerable populations like senior citizens, children and pregnant women must be alert and take precautions.

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With the monsoon becoming active, public health specialists have indicated that in the coming months, there is a chance in the rise of influenza cases, largely due to the subtype H3N2, which was detected earlier this year in Maharashtra, Telangana, Kerala and many other Indian States.

In the past one week, due to widespread rains, influenza due to H1N1 (swine flu) and its subtype H3N2 have already started to rise in parts of Maharashtra, especially in Mumbai. Patients who have fallen sick due to H3N2 are recovering after 8 to 15 days but they continue to experience lethargy for some more time.

The symptoms of H3N2 are typical for any kind of influenza infection. Highlighting the symptoms of influenza, the Indian Council of Medical Research (ICMR) in its guidelines says “The hallmark of influenza is the sudden, rapid onset of symptoms. Influenza symptoms may include fever, chills, body aches, sore throat, non-productive cough, runny nose and headache. Gastrointestinal symptoms and muscle inflammation occur more often in young children, and infants can present with a sepsis-like syndrome”.

Influenza detected in Hyderabad twice a year

During the peak of H1N1 (formerly swine flu) between 2016 and 2017, the district-level surveillance of positive infections, ground-level observations and secondary data analysis of positive patients, had given a clear indication that influenza has become a twice-a-year affair.

The secondary data analysis of swine flu positive cases in Hyderabad had clearly pointed towards a ‘bi-modal peak observed with increase in the number of cases from January and a second peak that will happen between July and August’. The data analysis study of H1N1, taken up by epidemiologists in Hyderabad had clearly established the timeline for possible future outbreaks of influenza infections in Telangana.

A similar study on influenza was conducted by epidemiologists and researchers in Andhra Pradesh after bifurcation between 2017 and 2018 at Sri Venkateswara Institute of Medical Sciences (SVIMS), which also indicated a similar trend that swine flu outbreaks happen twice in a year in AP.

The public health specialists also had calculated the influenza Case Fatality Rate (CFR), which indicated that it was high among women between the age 15 years and 44 years, and greater than 60 years. Among males, the CFR was high in the age groups of 45 years to 59 years.