In April 2009, the first case of influenza A H1N1 was reported in Mexico. Later the infection spread and a total of 214 countries were affected by the pandemic worldwide. Ten years since, influenza H1N1 has become a seasonal virus, according to the Centers for Disease Control (CDC) in Atlanta.
Yet, in India, the past decade saw as many as 1.58 lakh persons being infected by the virus and over 10,000 succumbing to it.
Maharashtra toll highest
An analysis shows that Maharashtra has reported the highest number of cases (33,284) and deaths (3,637) since pandemic influenza struck in 2009. Continuous and intensified surveillance, testing of throat swab samples at both National Institute of Virology (NIV) in Pune and private laboratories and death audits helped the state health authorities towards early identification of cases.
According to Dr Pradeep Awate, Maharashtra’s surveillance officer, the surveillance systems and diagnostic capacities in the state are strong, which led to the reporting of the maximum number of cases and deaths. Awareness levels were high especially regarding home-based isolation of persons with the flu. In other states, surveillance may not be as good, experts have pointed out.
Virus in circulation, evolving
Unlike the temperate countries, where peak influenza activity is recorded in winters, in the tropical and sub-tropical countries, the primary peak of influenza activity is during the monsoon. However, in some places, influenza also peaks during winters and in some tropical countries, influenza sustains throughout the year.
According to experts at NIV Pune, scientists have tested over 65,000 patients’ samples in the past 10 years. If testing is stopped, it would seem there is no disease. But the virus is very much in circulation. Overcrowding leads to increased transmission of airborne infection. Some areas in the country may have a sparse population but with diagnostic testing facilities being set up, more cases are being detected.
Rajasthan worst hit in 2019
Increased testing in states like Rajasthan and Gujarat has resulted in more cases being reported. According to the National Centre for Disease Control data, Rajasthan is the worst hit this year with 5,040 cases and 206 deaths. From 2010 till mid-August this year, Rajasthan has seen 21,107 cases reported and 1,638 deaths while Gujarat has reported 25,219 cases and 1,897 deaths. This year Gujarat has reported 4,819 cases and 149 deaths, followed by Maharashtra which has registered 2,135 cases and 202 cases.
N-E states also affected
In the National Medical Journal of India, NCDC researchers have, in their 2019 study ‘Influenza A (H1N1) in India – changing epidemiology and its implications’, reported that 2017 was an unusual year. According to researchers Dr S Kulkarni, Dr S Singh and others, the geography of the influenza A (H1N1) virus seems to have been affected.
While cases used to come mainly from western parts of India and localised to districts like Pune in Maharashtra and Jaipur in Rajasthan, northeastern states like Arunachal Pradesh and Tripura, which had never reported influenza A (H1N1) cases in the past, notified 44 cases in 2017.
This year, Tripura registered 31 cases, Sikkim reported eight, while Meghalaya and Manipur reported two each. According to Dr Kulkarni, in 2017 the virus showed epidemiological characteristics different from previous years. Researchers said these observations require further probe to understand the changing ecological and transmission dynamics, as well as potential changes in awareness and testing. Monitoring of the genetic character of the virus and surveillance for drug resistance in the context of influenza A (H1N1) and other influenza viruses remain a high priority, said Dr Kulkarni.