A five-year study of Influenza A (H1N1) pandemic 09 from Central India

Introduction : Influenza virus is a typical human pathogen causing serious respiratory infection. While declaring the last pandemic to be over in August 2010, World Health Organisation (WHO) conveyed that Pandemic Influenza A (HINI) virus would circulate as Seasonal Influenza virus for years to come. This study was undertaken to observe trends of Influenza A (H1N1) pandemic 09 over last five years in Vidarbha region of Maharashtra. Material and Methods: Throat/nasal/nasopharyngeal swabs/aspirates from clinically suspected cases of influenza like illness in category C received in the Viral Research and Diagnostic Lab (VRDL), Indira Gandhi Govt Medical College (IGGMC), Nagpur from October 2015 to September 2019 were included in the study. The samples were tested by reverse transcriptase real time polymerase chain reaction (RT-PCR). Clinical and epidemiological parameters were also noted. Results : Influenza A(H1N1)pandemic 09 positivity ranged from 03% to 21% in last five years. Males and females were almost equally affected except in 2019. Maximum positive cases were seen in age group of 41-60 years in 2015 (24%), 0-10 years in 2017(24%), 21-40 years in 2018 (9%) and 11-20 years (26%) in 2019 . Dual peaks of infection were seen in 2017, 2018 and 2019. Bhandara, Gondia and Akola districts had highest positivity . Discussion : Influenza A(H1N1)pandemic 09 is showing shift towards younger age groups and females slightly, both of which needs attention. Waning and waxing trend in last five years indicate unpredictable and changing epidemiology of the virus which should be studied further in details with respect to time, place, person and molecular characterisation of the virus. © 2020 Published by Innovative Publication. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by/4.0/)


Introduction
Respiratory infections due to influenza virus are a major cause of morbidity and mortality all over the world. The first case of influenza A H1N1 was reported from Mexico in April, 2009. 1 Subsequently, the infection spread to across 74 countries with 30, 000 confirmed cases on June 11, 2009. This prompted the World Health Organization to raise the warning from phase 5 to phase 6. 2 This was a new strain of the virus which was never seen before. Total 214 countries were affected by the pandemic worldwide. In India, the first case of influenza A H1N1 was reported on May 16, 2009 from Hyderabad. 3 The World Health Organization declared the post pandemic phase on August 10, 2010. 4 Subsequently, the influenza activity in the six regions of the world is on decline. 5 This pandemic A(H1N1)2009 virus has been widely circulating across the globe since 2009, and is now established in human populations as a seasonal influenza virus. Currently there is no longer a pandemic virus circulating in the world. 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. IDSP data show that the epidemiology of influenza A (H1N1) is changing in terms of geographical distribution, age and seasonality. 6 In view of lack of epidemiological information on trends

Ethical committee
Samples were processed as undera) Ribonucleic acid (RNA) extraction -Coloumn based extraction was performed by QIAmp ® viral RNA Mini Kit from Qiagen, USA. b) Mastermix preparation -Mastermix was prepared by using following components and concentration and Extracted RNAs added last into the mix- Primer probe sequence's that were used in the study were as followsd) RT-PCR : Samples were tested by reverse transcriptase realtime PCR (RT-PCR) for influenza type A using Step e) Results were interpreted depending upon the Cycle Threshold (C T ) values. Curve for the given target was considered as positive if it crossed the threshold on or before 35 cycles. All samples indicated a positive curve for RNase P (crossed the threshold on or before 35 cycles, indicating the presence of sufficient human RNase P gene). Positivity for RNase P gene is a marker to assess the quality of the specimen.
f) Interpretation - During the study period, a total of 3690 samples were received for testing. Of these 3690 samples, 553 (15%) samples tested positive for influenza A H1N1 pandemic 09.
Year wise distribution of cases is shown in Figure 2 . From 2015 -2019, no. of females patients suspected to be having Influenza A (H1N1)pandemic 09 infection were more than male patient but positivity was almost equal throughout these years except in 2019 (M/F positivity was 7/12 %) as shown in Table 3. In 2015, maximum affectivity was seen in age groups 21-40 and 41-60 years, which changed to 0-10 years in 2017 followed by again 21-40 years in 2018 and 11-20 years in 2019 as shown in Table 4. Looking at the districts most affected, in 2015 , Bhandara , Gondia and Wardha were most affected. In 2017, again Bhandara district was hit the most by the virus followed by Chandrapur district. In 2018, again Gondia had highest positivity and in the current year, Akola is the worstly affected district which was never in top three hit list districts from 2015 to 2017. From 2018, Akola came into top three districts with highest H1N1 positivity. Table 5 shows districtwise distribution of cases. Influenza A (H1N1) pandemic 09 is known to circulate in between Aug-Nov months. In last five years, we have seen peaks of infection in this same time period but peaks have also been noted in summer months ( Figure 3). Clinical features associated with the infection are mentioned in Table 6.  and Madhya Pradesh with more number of deaths in Rajasthan and Gujarat. 8 Integrated Disease Surveillance Programme (IDSP) data show that the epidemiology of influenza A (H1N1) is changing in terms of geographical distribution, age and seasonality but studies related to this are scarce. In our study, we tried to focus on changing trends of influenza activity in central India. Influenza activity continue to be reported every year, more during winter. However, as per IDSP data, 2017 was an unusual year, with the virus spreading rapidly throughout the country, and showing different epidemiological parameters as compared to previous years in terms of period (two peaks observed), place (infection reported for the first time from some of the north-eastern states) and person (comparatively more cases among children). 9 In our study , we found maximum  10 But some studies showed winter prevalence of H1N1 11,12 and some showed post monsoon peaks. 13,14 In one more study by Broor et al., maximum cases were reported in rainy season. 15 Dual peaks have also been reported from other Indian author's 16 and other parts of the globe. 17,18 Althrough these years, age group 21-40 and 41-60 years were mostly affected in our study. Since 2017, we noted shift in age group towards 0-10 and 11-20 years. In 2018    and 2019, again younger age groups found to be mostly affected in our study. In a study by Ganesh Nandhini et al., maximum positivity was seen in age group 20-49 years 19 and in 51-60 years by Prasad S et al. 20 While Siddharth et al. 12 stated that influenza A H1N1 pandemic 09 relatively spared the older population and had stricken the younger population. The age shift in our study shows that virus has now started establishing in all age groups more towards younger population. This needs high alert suspicion of the infection and demands increased attention. Majority of the positive cases had the clinical manifestations of fever, breathlessness, cough, followed by sore throat and myalgia. Apart from respiratory symptoms, cases also presented with diarrhea, nausea, haemmorhagic manifestations and conjunctivitis. In a study, the main presenting symptom was fever that is 83.3%, followed by dyspnea (76.7%), cough (70%), throat pain and least common was chest pain. 21 27 This is not an antigenic shift but a minor drift, but this change in circulating strain should be a focus of future research. WHO listed the virus in 'Top Ten Threat's' world can face in 2019. Who says-'The world will face another influenza pandemic -the only thing we don't know is when it will hit and how severe it will be. Global defences are only as effective as the weakest link in any country's health emergency preparedness and response system.' 28

Conclusion
Although the pandemic era of H1N1 has settled, epidemics are a constant reminder of the hidden danger. Silent spread of the virus has to be kept an eye on to see -What is changing/ changed/ expected to change ?

Acknowledgment
We are thankful to DHR-ICMR, New Delhi for their financial support and to NIV, Pune for their constant support and guidance. Thanks are also due to Asmita Babhulkar and Harish Nimbhorkar for their technical support.

Source of funding
None.

Conflict of interest
None.