Influenza season has changed

It was once widely believed that winter is the season for influenza, a contagious viral infection of the respiratory system. However, epidemiologists now report a significant shift in this pattern. Influenza is currently appearing most frequently during the summer and monsoon seasons. Alongside seasonal influenza, several cases of avian influenza or bird flu have also been detected among humans this year. The public health experts are viewing it as a new potential risk.

Discussing this shift in influenza trends, Professor Tahmina Shirin, Director of the Institute of Epidemiology, Disease Control and Research (IEDCR) told Prothom Alo, “Our regular surveillance indicates that influenza remains more prevalent for about six months. It begins to rise in April and starts to decline from September. The highest number of cases is observed in June, July, and August, during the summer season, while winter shows the lowest incidence.”

Public health experts identify five groups as being at the highest risk of influenza infection: the elderly, children less than five years of age, individuals with comorbidities, pregnant women and healthcare workers.

Findings of IEDCR
Since 2007, the IEDCR and the International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b) have jointly conducted influenza surveillance in 19 government hospitals – nine district hospitals and 10 tertiary-level hospitals. To monitor the situation, patient samples are regularly tested, which also helps detect other infections, including bird flu.

An analysis of samples collected between January 2007 and December 2024 revealed that July consistently recorded the highest proportion of influenza-positive cases, with an average detection rate of 30.85 per cent. The data from the past 17 years show that detection rates begin increasing from April (11.86 per cent), continue to rise through May (21.86 per cent) and June (29.10 per cent), peak in July and then decline through August (22.25 per cent) and September (18.86 per cent).

The lowest detection rates occur during December (2 per cent) and January (1.74 per cent).