Why are swine flu & seasonal influenza spiralling? How do you know Covid-19 from seasonal flu?

The past two years were largely uneventful with respect to swine flu and/or seasonal influenza cases and related mortality. We are again witnessing a surge this year. What is driving it?

The term, swine flu, is used for the 2009 H1N1 strain, which was a recombinant of influenza viruses in birds, pigs and humans. The strain evolves every year, which is why these subsequent strains are termed under the broad category of seasonal influenza. The surge in seasonal influenza cases in a specific year depends on the general population’s immunity to the specific strain circulating in a specific year. We are seeing swine flu patients and seasonal influenza patients at present as both the viruses are in circulation. If we look at the epidemiology of seasonal influenza, it circulates in the community in tropical countries throughout the year with two big spikes — first in winter and the second in the monsoon. So this is the time when we expect an increase in the number of seasonal influenza cases. This is a major difference compared to temperate countries such as the US or Europe where only one surge is seen in the year that is winter.

Right now we can say we are seeing an equal number of Covid-19 and seasonal influenza patients. In fact, the number of seasonal influenza cases is more compared to the last two years. That may be because we are not strictly wearing masks and sanitising hands, something that we did consistently through the two years during Covid-19. These are two important non-pharmaceutical interventions, which reduce the susceptibility to seasonal influenza as well as Covid-19. Furthermore, routine vaccination for seasonal influenza has gone down. It is not being highly recommended in high-risk groups by the government unlike pre Covid-19 years and has now taken a backseat following Covid-19. We can control the number of seasonal influenza patients in the community through vaccination and post-exposure prophylaxis with Oseltamivir (Tamiflu). We should promote an annual shot of the seasonal influenza vaccine in the media also.

How does seasonal influenza impact an individual’s morbidity risk?

Like Covid-19, those with co-morbidities are at a high risk of disease progression and complication when it comes to seasonal influenza. We are seeing that there is mortality in patients with significant co-morbidities. The sensitivities are almost the same as those for Covid-19 — haemato-oncological problems, malignancy, post-transplant cases, chronic obstructive lung disease, obesity, diabetes and so on.

In terms of susceptibility to seasonal influenza, it is more or less equal across all age groups, except in paediatric patients and those aged above 65 years. These two groups are such that even without any co-morbid conditions, they are more prone to disease severity. For a majority of youngsters, most of whom are immuno-competent, seasonal influenza is a self-limiting disease. Symptoms include high grade fever, throat pain, headache, body pain, runny nose, which last for five to seven days or so. Then they report spontaneous and uneventful recovery. Taking fever-reducers such as Paracetamol work for healthy immuno-competent individuals but for paediatric and aged people, and those with comorbidities, we generally prescribe the antiviral drug Tamiflu, a very effective agent for influenza.

With fever being the first symptom and the monsoon known for the resurgence of viral infections, seasonal influenza, vector-borne diseases, and now Covid-19, what should one look out for?

With most viral infections, including dengue fever, the first episode is usually self-limiting in immuno-competent people. Such individuals report an uneventful recovery without much medical intervention. But those in high risk and co-morbid groups, should not ignore their fever, visit their doctor, get tested and secure a definite diagnosis.They should get a diagnostic evaluation done on the first day of the onset of symptoms rather than waiting for a few days as by then the disease can progress and complications may crop up. For healthy individuals who do not have many symptoms, except for fever and body pain, there is not much cause for worry. Their assessment and evaluation should be symptom-driven.

With Covid-19 and seasonal influenza circulating in the population, how do we go about the diagnosis, given that most individuals just opt for a Covid-19 test? Surely a negative Covid-19 test doesn’t rule out an individual’s probability of seasonal influenza instead?

We usually recommend the RT-PCR for both COVID-19 and seasonal influenza. In clinical practice, we have multiplex PCR. This assay includes a target panel of all the common viruses producing respiratory symptoms. So a single multiplex PCR can confirm whether it’s influenza A, influenza B, parainfluenza, COVID19, swine flu or other respiratory viruses. But it is very expensive, costing around Rs 11,500 or so, as it checks multiple pathogens. The results come within two-and-a-half hours and are highly reliable.

How is a confirmed diagnosis of the type of seasonal influenza one is afflicted with significant for health management?

Knowing the final and confirmed diagnosis is very important, as for the three viruses — influenza A, B and swine flu — Tamiflu is highly effective. Besides, most of these patients will respond to the antiviral drug within 48 hours of taking it. This is also one of the diagnostic traits that can be an indicator. So basically if someone improves markedly after taking Tamiflu, it can be said that he/she has been affected by one of the three viruses. That apart, a PCR test can tell you which kind it is because symptoms are more or less the same for seasonal influenza, swine flu or influenza B virus. From a clinical examination perspective, one can say that an individual has seasonal influenza but for the specific virus, only a PCR test can give a final and confirmed diagnosis.