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Year : 2016  |  Volume : 59  |  Issue : 1  |  Page : 63-65
Influenza A(H1N1)pdm09 cases in sub-Himalayan region, 2014-2015 India

Department of Microbiology, Indira Gandhi Medical College, Shimla, Himachal Pradesh, India

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Date of Web Publication9-Mar-2016


Current influenza A(H1N1)pdm09 strain severely involved many parts of the country. The study was conducted to analyze the clinicoepidemiological trend of influenza A(H1N1)pdm09 cases from October 2014 to March 2015. Samples processing was done as per the Center for Disease Control guidelines. A total of 333 specimens were processed out of which influenza A(H1N1)pdm09 constituted 24% (81) of total, 5% (18) cases were seasonal influenza A virus strains. Mean age group involved was 49 years with case fatality rate of 20%. Patients died were 63% males and 44% had comorbidities, and among them, 38% patients died within 24 h of hospitalization. The mean age of comorbid patients who died was 59 years; whereas the mean age of patients died having no co-morbidities was 41 years (P < 0.005). Mortality was seen among 81% (13) of patients who were on ventilator support. Added mortality in specific human group demands continuous surveillance monitoring followed by the detection of mutation, even in susceptible animal population.

Keywords: Influenza A(H1N1)pdm09, seasonal flu, surveillance

How to cite this article:
Sharma P, Gupta S, Singh D, Verma S, Kanga A. Influenza A(H1N1)pdm09 cases in sub-Himalayan region, 2014-2015 India. Indian J Pathol Microbiol 2016;59:63-5

How to cite this URL:
Sharma P, Gupta S, Singh D, Verma S, Kanga A. Influenza A(H1N1)pdm09 cases in sub-Himalayan region, 2014-2015 India. Indian J Pathol Microbiol [serial online] 2016 [cited 2021 Oct 28];59:63-5. Available from: https://www.ijpmonline.org/text.asp?2016/59/1/63/178222

   Introduction Top

From 11 June 2009 to August 2010, humanity faced the WHO phase 6 pandemic alert by influenza A(H1N1)pdm09. Starting in Mexico, in April 2009, it has caused 18,300 deaths across 74 countries. [1] In August 2010, postpandemic period started and after that pH 1N1 has become the circulating strain. It is now a human seasonal flu virus also circulating in pigs.

Mortality associated with virus in India was 981 in 2009, 1763 in 2010, 75 in 2011, 405 in 2012, and 692 in 2013. [2] Until 11 March 2015, 27,886 cases and about 1587 deaths with a case fatality rate (CFR) of 57 per 1000 cases have been reported from India. [3]

Present high CFR and transmission of influenza A(H1N1)pdm09 might be due to prolonged dip in temperature, Telangana, traditionally tropical state has experienced excessive humidity, coldest winter in the last 20 years with temperatures dipping to single digits, and frequent travel. Recent study at MIT suggested that Indian swine flu strain (A/India/6427/2014) contain amino acid changes T200A and D225N as compared to influenza A(H1N1)pdm09 due to that it has increased ability of binding to human glycan receptors, fusion and transmission resulting in high virulence, and increased disease severity and decreased susceptibility to neuraminidase inhibitors leading to increased hospitalizations and deaths. [4]

The present study was conducted at regional influenza surveillance center, Indira Gandhi Medical College, Shimla, to analyze the clinicoepidemiological trend of influenza A(H1N1)pdm09 cases in the sub-Himalayan region, especially during 2014-2015 in India.

   Materials and methods Top

Prospective hospital-based study from October 2014 to March 2015 was done at Indira Gandhi Medical College, Shimla, Himachal Pradesh. A total of 333 throat/nasopharyngeal swabs from patients suspected of category C were collected in viral transport medium, transferred in the cold chain, and processed in the Department of Medical Microbiology, Indira Gandhi Medical College, Shimla. [5] QIAamp® viral RNA Mini Kit (Qiagen, USA) was used for RNA extraction and reverse transcription and amplification of the target genes was carried out using relevant primers and probes (TaqMan® Universal PCR Master Mix and H1N1 influenza A MGB Assay [Set 1 and 2], Applied Biosystems, USA) on an ABI 7500 cycler (Applied Biosystems, USA). [6] Four target genes were amplified in each specimen; Inf A, Universal swine (swFluA), Swine H1 (swHI), and RNaseP (RP). [6] Specimens, where RP was not detected, were considered a faulty collection.

The data was analyzed using Epi info 7 (7.1.3) CDC Atlanta, Georgia (USA), November 2013. [7] Yates corrected Chi-square (χ2 ) test was used, and a P ≤ 0.05 was considered statistically significant.

   Results Top

A total of 333 cases suspected of influenza A(H1N1)pdm09 under category C were tested during the study period. Influenza A(H1N1)pdm09 constituted 24% (81) of total, 5% (18) cases were due to other circulating influenza A virus strains (OCIA), and 2% (6) of specimens had a faulty collection.

None of the study population had the history of influenza vaccination. These cases are sporadic and occurred at distances kilometers apart.

The mean age of the patients affected by influenza A(H1N1)pdm09, in 2015, was 45 years and by OCIA was 51 years (P = 0.3). Sex distribution being 54% (44) and 56% (10) males by influenza A(H1N1)pdm09 and OCIA, respectively. CFR for influenza A(H1N1)pdm09 was 20% (16/81).

Patients who died due to influenza A(H1N1)pdm09 had the mean age of 49 years, 63% (10) males and 44% (7) had associated comorbidities mainly involving respiratory systems such as chronic obstructive pulmonary disease. A total of 38% (6) patients died within 24 h of presentation to the hospital. The mean age of patients with comorbid conditions who died was 59 years, whereas the mean age of patients who died having no comorbidities was 41 years (P < 0.005). Duration of illness among who died due to influenza A(H1N1)pdm09 was <3 days in 69% (11) of cases. Mortality was seen among 81% (13) of patients who were on ventilator support.

   Discussion Top

Influenza A(H1N1)pdm09 attributed to 80% of influenza A infections, whereas OCIA constituted only 20% of influenza A cases in 2015. In Himachal Pradesh, similar distribution in a number of cases between influenza A(H1N1)pdm09 and OCIA was seen during pandemic phase but with a declining trend, thereafter, up to 2012. Since 2009 through 2014, the number of cases of influenza A(H1N1)pdm09 as compared to OCIA were 50% (22), 30% (17), 30% (15), 44% (4), 70% (33), and 44% (4). [8]

Influenza A(H1N1)pdm09 outbreak has taken place in different states in India in 2014-15. An epidemic was declared in Rajasthan on 12 February 2015. [9] In India, during 2014-2015, influenza A(H1N1)pdm09 severely involved in Rajasthan (6093 cases and 358 deaths), Gujarat (5969 cases and 368 deaths), and Maharashtra (2890 cases and 235 deaths). [3]

Increase in a number of cases might be attributed to prolonged dip in temperature and excessive humidity. It is suggested by some researchers that the present Indian strain has acquired certain mutations, leading to increased virulence. [4] Distant cases may be due to carrier state which were asymptomatic or have subclinical infection.

No increased CFR was seen in 2015 strain (20%). This picture simulates the situation in the postpandemic period of 2010 through 2014, where CFR of around 18% was observed. [8]

Two patterns were observed in mortality. Healthy adults and old people with co-morbidities died almost equally in number due to influenza A(H1N1)pdm09. This may be due to the lack of immune memory among the younger population as compared to the elderly who had acquired it during previous pandemics. [10]

The majority of influenza A(H1N1)pdm09 deaths occurred within 3 days of disease onset, which can be attributed to the increased virulence of the strain. [4]

Age and sex predilection does not vary among influenza A(H1N1)pdm09 and OCIA strain in 2015.

   Conclusion Top

Sporadic increase in seasonal flu cases due to influenza A(H1N1)pdm09 was seen with no increase in CFR, but mortality among healthy adults occurred at par with old with co-morbidities. We suggest continuous surveillance and monitoring of influenza-like illness followed by sequencing to detect mutation if any at an early stage. Similarly, surveillance of infection is also recommended for the susceptible animal population.


We acknowledge Mr. S.D. Verma, Mr. B.D. Negi, and Mr. Pradeep Kashyap for expert technical support.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

Cheng VC, To KK, Tse H, Hung IF, Yuen KY. Two years after pandemic influenza A/2009/H1N1: What have we learned? Clin Microbiol Rev 2012;25:223-63.  Back to cited text no. 1
Ministry of Health and Family Welfare, India Information on Swine Flu, New Delhi. MOHFW. Available from: http://www.mohfw.nic.in/showfile.php?lid=1174. [Last retrieved on 2015 Mar 27].  Back to cited text no. 2
"Swine Flu in India: 2,035 Succumb to the H1N1 Virus". HealthSite. March 30, 2015. Available from: http://www.thehealthsite.com/news/swine-flu-in-india-2035-succumb-to-the-h1n1-virus/ [Last retrieved on 2015 Mar 30].  Back to cited text no. 3
Tharakaraman K, Sasisekharan R. Influenza surveillance: 2014-2015 H1N1 "swine"- derived influenza viruses from India. Cell Host Microbe 2015;17:279-82.  Back to cited text no. 4
"CD Alert". Monthly Newsletter of National Centre for Disease Control, Directorate General of Health Services, Government of India. Vol. 13. 2009. p. 1-8.  Back to cited text no. 5
World Health Organization. CDC protocol of realtime RTPCR for swine influenza A (H1N1). Geneva: World Health Organization; 2009. p. 1-8.  Back to cited text no. 6
Epi info 7 (7.1.3), November 2013. The division of surveillance and epidemiology. Atlanta, USA: Centers for Disease control and Prevention; 2013.Available from: https://wwwn.cdc.gov/epiinfo/7/index.htm. [Last retrieved on 2015 Feb 27].  Back to cited text no. 7
Mehta VK, Sharma P, Guleria RC, Ganju S, Singh DV, Kanga A.Clinico-epidemiological profile, pandemic influenza A H1N1/2009 and seasonal influenza, August 2009-March 2013, Himachal Pradesh, India. Indian J Community Med 2015. [In press].  Back to cited text no. 8
"Rajasthan Declares Swine Flu Epidemic". Business Standard. February 13, 2015. Available from: http://www.business-standard.com/article/current-affairs/rajasthan-declares-swine-flu-epidemic-115021201672_1.html. [Last retrieved on 2015 Feb 22].  Back to cited text no. 9
Fajardo-Dolci G, Gutierrez JP, Arboleya-Casanova H, Garcia-Saiso S. Comparing deaths from influenza H1N1 and seasonal influenza A: Main sociodemographic and clinical differences between the most prevalent 2009 viruses. Influenza Res Treat 2012;2012:501784.  Back to cited text no. 10

Correspondence Address:
Pooja Sharma
Department of Microbiology, Indira Gandhi Medical College, Shimla - 171 001, Himachal Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0377-4929.178222

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