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Year : 2020  |  Volume : 25  |  Issue : 1  |  Page : 23-27

Investigation of H1N1 influenza outbreak in a remote hilly region of North India

1 Department of Community Medicine, Indira Gandhi Medical College, District Shimla, Himachal Pradesh, India
2 Office of Chief Medical Officer, District Shimla, Himachal Pradesh, India
3 Department of Orthopaedics, Indira Gandhi Medical College, District Shimla, Himachal Pradesh, India
4 Department of Community Medicine, Shri Lal Bahadur Shastri Government Medical College, Mandi, Himachal Pradesh, India

Date of Submission03-Nov-2018
Date of Acceptance04-Sep-2019
Date of Web Publication14-Apr-2020

Correspondence Address:
Dr. Vijay Kumar Barwal
Department of Community Medicine, Indira Gandhi Medical College, Shimla, Himachal Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jmgims.jmgims_59_18

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Background: Influenza A/H1N1/2009 Pandemic strain is one of the reemerging viral diseases. Localized outbreaks of various magnitudes continue to occur globally as well as in India. An outbreak of this disease took place in a remote area of North India. We investigated it to find out the etiology and distribution and recommend appropriate control measures. Materials and Methods: On urgent directions from the State Health Department, a team was constituted to investigate the outbreak. The team mapped the area and undertook house to house search of cases on 17th–19th May 2017. Line listing of cases was prepared. Respiratory samples of 13 symptomatic cases were taken. Eight blood samples were also collected for viral serology and blood cultures. Results: Line listing consisted of 61 cases. Attack rate was 25.2/1000 population. Mean age was 13.9 years with a median of 4 years. All cases had fever, followed by cough (67.2%) and sore throat (44.3%). Case–fatality ratio was 1.6%. Epidemic curve showed a common source continuous epidemic with limited spread. The average incubation period was 5 days. Four samples were positive for Influenza A/H1N1/2009 Pandemic strain and two were positive for Influenza A (nonswine). Conclusion: It was a confirmed outbreak of pH 1N1. A similar outbreak here in April 2010 suggests the endemic presence of this virus, and in future, as the susceptible population again rises to a threshold level, another outbreak may occur in this area. Utmost priority should be accorded for continuous monitoring and surveillance along with intensified IEC activities.

Keywords: Pandemic Influenza A, H1N1, outbreak investigation

How to cite this article:
Barwal VK, Thakur HR, Bhushan B, Thakur SP, Chaudhary A, Sharma GA. Investigation of H1N1 influenza outbreak in a remote hilly region of North India. J Mahatma Gandhi Inst Med Sci 2020;25:23-7

How to cite this URL:
Barwal VK, Thakur HR, Bhushan B, Thakur SP, Chaudhary A, Sharma GA. Investigation of H1N1 influenza outbreak in a remote hilly region of North India. J Mahatma Gandhi Inst Med Sci [serial online] 2020 [cited 2021 May 6];25:23-7. Available from: https://www.jmgims.co.in/text.asp?2020/25/1/23/282359

  Introduction Top

Influenza A/H1N1/2009 Pandemic strain (pH1N1), is an acute viral reemerging respiratory infection causing significant morbidity and mortality worldwide.[1],[2] It was first detected in North America in April 2009,[3] spread rapidly and was declared a pandemic in June 2009. There were estimated 201,200 respiratory deaths world over associated with pH1N1.[4]

In India, the first case was reported on May 16, 2009, from Hyderabad.[5] Till August 20, 2017, there were 22,186 cases with 1094 swine flu deaths.[6] Localized outbreaks continue to occur globally as well as in India.[7] The central and state governments have taken the epidemic very seriously with several interventions including the epidemic preparedness plan.[8]

A similar pH1N1 outbreak, with one death, was first reported in local newspapers from a very remote area of Shimla in Himachal Pradesh. We investigated it to find out the etiology and distribution, and recommend appropriate control measures.

  Materials and Methods Top


Malat Panchayat with a population of 2417 is located in Kupvi area of Health Block Nerwa, Tehsil Chopal, District Shimla, Himachal Pradesh. It is a very remote area, situated at an average altitude of 7500 feet above sea level. It is a cluster of ten villages and is about 170 km from the district headquarter Shimla. It has a very hostile terrain and is very difficult to reach with about 50 km of the hilly road being unmetalled and bumpy. A large part of the Panchayat still has to be accessed on foot.

On May 16, 2017, information was received from the local health officials, with simultaneously news appearing in the local print media that a child had died due to some mysterious fever in Kupvi area of Shimla District. Several others, mostly children, were also reported suffering from the same illness. As per urgent directions from the State Health Department, a team including the district health officer, an epidemiologist, a pediatrician (as most cases were in the pediatric age group), block medical officer, a local medical officer from Community Health Centre, Kupvi, lab technician, pharmacist, and health supervisor, was constituted to investigate this outbreak, identify the disease and mode of transmission, treat the cases, and suggest control measures. Before departure from the district headquarters, the team had a telephonic conversation with the local medical officers who had already visited the area on the same day, i.e. May 16, 2017. Preliminary information regarding signs and symptoms and patients affected with the illness were discussed, and preparations for medical, epidemiological, and laboratory investigations were done accordingly. Based on the common differential diagnosis of fever with the given sign and symptoms and further consultation with the Department of Microbiology, Indira Gandhi Medical College Shimla, requisite kits were prepared to be carried along by the team and to collect and bring back the laboratory samples for testing.

Ethical issues

This outbreak investigation was done as a public health containment measure on the direction of State health authorities. Hence, it was deemed as a nonresearch, but we conformed to all other guidelines mentioned in the Declaration of Helsinki. Informed consent was obtained from all the participants and confidentiality of all the cases was maintained.

Case definition

A case of influenza-like illness (ILI) was defined as an acute onset of fever (>38°C) with or without cough or sore throat in the absence of any other diagnosis residing in the villages of Malat Panchayat. All the patients who were found during the house-to-house search, meeting the above criteria, and falling sick within the preceding 1 week of reporting of the index case, i.e. on or after May 4, 2017, were included for line listing. A person with ILI with laboratory confirmation for influenza A (H1N1) on a throat swab by real-time reverse-transcriptase polymerase chain reaction was considered as confirmed case of pandemic influenza (H1N1).[9]

Data collection

The team reached the area on afternoon of May 17, 2017, mapped the area, and started the investigation with house-to-house search of cases (symptomatic or cured) on 18th and 19th May 2017. A few of the affected villages of this Panchayat, namely Malat, Shivdhar, Ahnog, and Cheendh had to be covered on foot (2–3 km each).

All the patients meeting the above case definition in the defined area were included for line listing. This line listing was done as per the annexure developed by Ministry of Health and Family Welfare, Government of India, for investigation of such an outbreak.[10] We collected information from all cases of ILI about the demographic details, residence, date of onset of illness, clinical details, immunization status, laboratory samples, and results of laboratory investigations, history of travel, and history of contact with suspected case of influenza (H1N1). Environmental conditions such as lighting, ventilation, overcrowding, and sanitation were also examined.

A total of 61 cases were line listed, 37 on the 1st and 24 on the 2nd day. All were immediately managed with appropriate treatment by the team. Medicines were dispensed on the spot. Two serious patients were referred to IGMC, Shimla, for investigation and further management. Seven other cases were admitted and put under treatment at nearby Community Health Centre, Kupvi.

Lab investigation

Respiratory samples (throat swabs) of only 11 symptomatic cases were taken. As two patients were referred to IGMC, Shimla, they were investigated managed at the tertiary institute itself. Blood samples (5 ml) were collected for viral serology and blood cultures, from suspected cases having recent onset of fever. The blood was allowed to clot and serum was transferred into another tube. Respiratory samples (throat swabs) were also collected and immediately stored in viral transport medium. All the samples were properly labeled and a list of these was prepared carefully. These were then transported under proper cold chain to the Department of Microbiology, IGMC, Shimla, for further investigations.

Data analysis

Data were entered in Microsoft Excel sheet and the clinical, demographic, and epidemiological data of the ILI cases were analyzed. Attack rate was calculated using the census population of all the villages as the denominator. Epidemic curve was drawn to find out the time distribution of cases.

  Results Top

The epidemiological profiles of all the cases with ILI were analyzed in terms of demographic characteristics, clinical presentation, and outcome. The line listing developed consisted of 61 cases, a majority of whom, i.e. 46 (75%) were children [Figure 1]. Attack rate was found to be 25.2/1000 population. The mean age of the cases was 13.9 years with a median age of 4 years. Most of the cases were below 15 years of age (72%), with a range of 7 months to 82 years.
Figure 1: Sex distribution of cases

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All the children had a history of fever (maximum 103 degrees F), majority also had cough (67.2%), while sore throat was reported by 44.3% cases followed by headache (36.1%), running nose (31.1%), and diarrhea (14.8%) [Figure 2]. History of respiratory distress was reported by one of the case, who unfortunately passed away during treatment. Majority (n = 44, 72%) of the suspected and laboratory-confirmed cases (n = 6, 100%) were in the age group of 0–14 years [Table 1]. All the cases, except one, recovered by treatment with oseltamivir, antibiotics, and paracetamol.[11] Case-fatality ratio was 1.6%.
Figure 2: Clinical symptoms observed

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Table 1: Involvement of different age groups and number of samples taken

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The epidemic curve does not have a clear single peak, showing that it was a common source continuous epidemic with limited spread. The average incubation period (IP) was 5 days with minimum and maximum IPs being 1 and 9 days, respectively [Figure 3].
Figure 3: Epidemic curve

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Out of 13 throat swabs taken (including two of referred patients at IGMC, Shimla) and sent for analysis, four were positive for Influenza A/H1N1/2009 Pandemic strain, while two others were positive for Influenza A (nonswine). Three of the six serum samples tested positive for Widal test and all were negative for scrub typhus. The blood culture report was found to be sterile [Table 1].

Probable cause of death of one child

There was sad demise of 1½ years, male child from village Shivdhar, PO Malat, Tehsil Kupvi, on dated May 12, 2017, cause of which was labeled as unknown fever. This was also one of the first three reported cases of ILI. He had a history of fever for 2 days, was admitted at CHC, Kupvi, was lethargic, and in shock, developed sudden respiratory distress with cyanosis and did not respond to treatment and in spite of all resuscitative measures could not be saved. During the investigation, we found that the other two siblings of this child, 4 years, Mch, and 3 years, Fch also had similar symptoms of fever, cough, sore throat, and running nose and came out to be laboratory-confirmed cases of pH1N1. Hence, the death of this child can be epidemiologically linked with pH1N1 infection.

Preventive and control measures

Apart from putting all the confirmed and suspected cases on symptomatic as well as antiviral treatment, the team also gave the residents of this area a health talk to decrease the panic as well as generate awareness about the disease. We talked about the prevention and control measures for this disease. The measures of personal hygiene such as handwashing and personal cleanliness were stressed upon. They were requested not to send the symptomatic children to school or “anganwadi” centers for at least 1 week or till the symptoms are over. Symptomatic family members were advised to use a separate room for at least 1 week or till the symptoms subside. Proper cross ventilation of rooms was also stressed upon, as inadequate natural ventilation was seen in most of the houses. In many households, although provision was there for cross ventilation, due to high altitude and temperate climate, most of the times, the doors and windows were kept closed. Hence, they were advised to keep them open for as long as possible for fresh air circulation.

If new cases with similar symptoms arise, they were advised to visit the nearest health center for checkup and necessary treatment. The block medical officer (BMO), Nerwa, was directed to continue IEC activities in and around the affected villages. The medical officers and health workers of the area were asked to attend and sensitize and spread awareness among the residents in the PRI meetings, VHSNC meetings, and during the morning school assemblies.

Contact tracing and oseltamivir prophylaxis

The household contacts of all the symptomatics were followed up for 1 week. Three symptomatic developed similar symptoms and were treated with antiviral (oseltamivir) treatment with necessary symptomatic management. Oseltamivir prophylaxis was also given to the close contacts of four cases from Malat Panchayat who were found positive for Influenza A/H1N1/2009 Pandemic strain and of the other two who tested positive for Influenza A (nonswine) strain. The hospital staff of CHC, Kupvi, which came in contact with these patients were also given oseltamivir prophylaxis for 10 days each. The block health supervisor was designated as the nodal officer to be in contact with the investigating team members, keep a watch on further activities and follow-up of the people who were treated with oseltamavir prophylaxis. None of them developed the symptoms of influenza.

  Discussion Top

India has witnessed localized outbreaks of H1N1 virus ever since the first appearance of this strain in 2009. Emergency response plan and enhanced surveillance measures since then have been initiated at national and local level.

Our results are consistent with the various H1N1 outbreaks that have taken place world over since the year 2009. In our study, the clinical attack rate was 25.2/1000. This was lower than that of a study done by Gurav et al. (71.1/100), although that was in a school setting.[12] The most common symptoms found by us were fever, cough, sore throat, and headache. This is comparable with most of the studies.[5],[12],[13],[14],[15],[16],[17] We also had 14.8% cases reporting with diarrhea which was higher than the one found by Biswas et al. (4%).[5] Looking at the figures of case-fatality rate, it was 1.6% in this outbreak. Studies worldwide have reported variable CFRs, ranging from 0.026% to 2.2%.[5],[16],[17],[18] Most of the suspects (72%) were in the age group of <15 years, and this is comparable with other studies[18],[19],[20] which report higher incidence in children. Surprisingly, the Kolkata study has reported the reverse, with highest suspects in 25–60 years age group. Six samples (46.2%) of 13 were positive for Influenza A and four (30.8%) were positive for Influenza A H1N1. This was higher than the study done by Raut et al.[14] who reported a positivity of 20%. Out of the six positive samples, we also found two Influenza A (nonswine)-positive cases. These results are not consistent with seasonal influenza, which is not so common in this age group.[21] The IP ranged from 1 to 9 days with an average IP of 5 days, which is consistent with the present literature for ILI.[17]

In the last 7 years, this same area has witnessed second such outbreak of Influenza H1N1. A similar outbreak was reported from the same area in April 2010, when four cases were tested positive.[22] During this outbreak, the three index cases, including the one child that died, had no history of travel out of the area. So probably, they contracted the infection from visitors or traveler (s) coming back, who were/was asymptomatic, or another reason can be that the H1N1 virus is circulating endemically in that area. The involvement of mostly the pediatric age groups also supports this, as they are known to have low immunity levels.[18],[19],[20]

It is also surprising that both the outbreaks occurred in the presummer and summer season, i.e. April and May, which is considered to be the low transmission season for Influenza H1N1.[17] This probably could have been due to the housing and more so due to the living conditions. Although the houses were spacious with no overcrowding, being a high altitude area with snow in winters, the residents have become habitual to keep the doors and windows closed. Hence, there is no proper cross ventilation. This facilitated the spread of infection within the household contacts. As it is a closed-knit community with frequent social gatherings, it further spread into the community.

  Conclusion and Recommendations Top

Thus, it was a confirmed outbreak of Influenza A/H1N1/2009 Pandemic strain in Malat Panchayat of Chopal Tehsil, Block Nerwa, District Shimla. Simultaneously, two positive cases of Influenza A (nonswine) shows that seasonal influenza virus was also in circulation/cocirculation. In this remote area where movement of people in and out of the area is difficult, and not frequent, a similar outbreak in April 2010 suggests the endemic presence of this virus.[22] Hence, a further study is strongly recommended to do a serosurvey of the healthy population and find out the prevalence of the H1N1 virus, as it may be constantly present and circulating in the form of asymptomatic carriers. This may have led to this outbreak, as well as the previous one in April 2010. According to our hypothesis, in future, when the susceptible population will again increase to a threshold level (decreased herd immunity), another outbreak may occur in this area, and further periodic outbreaks may continue to occur.

Although vaccination of all the susceptible is debatable for a developing country like ours, many experts have started advising the “flu” vaccine,[23] and due to this awareness, some people are voluntarily coming for vaccination. We should give utmost priority for continued monitoring and surveillance in this area, along with continuous IEC activities.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

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