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 Table of Contents  
Year : 2017  |  Volume : 19  |  Issue : 2  |  Page : 142-145

Control of H1N1 influenza outbreak: A study conducted in a naval warship

1 PMO, INS Kadamba, Karwar, Karnataka, India
2 SSO(H), HQWNC, Mumbai, Maharashtra, India
3 Respiratory Physician, INHS Asvini, Mumbai, Maharashtra, India
4 PMO, INS Kochi, Mumbai, Maharashtra, India

Date of Web Publication13-Feb-2018

Correspondence Address:
Dr. Sougat Ray
SSO(H), HQWNC, Mumbai - 400 005, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jmms.jmms_70_17

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Introduction: In confined afloat settings, the threat of an acceleration of the Influenza outbreak is substantial, causing high morbidity of the personnel on board, disrupting daily activities, and leading to low crew morale. In this study, H1N1 Influenza outbreak in a Naval Warship and its control measures are described. Materials and Methods: It is a study of 21 clinically suspected cases of H1N1 Influenza. Cases were reported within 3 weeks from a ship company, all of whom were susceptible. They have been described on the basis of demography, clinical features, recent travel history, and history of contact. Results: Mean age of the clinically suspected cases was 26.71 years. Of 21 suspected cases, 14 were found positive for the disease. Nine cases were admitted to the hospital and two developed complications. Attack rate of the disease was 4.83%. Conclusion: In confined afloat settings, prompt public health measures of active case finding, strict isolation, and adherence to hand hygiene, following cough etiquettes and disinfection enhancement, can effectively mitigate the outbreak. Vaccination may not have a role to play if preventive measures are instituted effectively.

Keywords: H1N1 influenza, outbreak control, ship, vaccination

How to cite this article:
Gupta A, Ray S, Tyagi R, Kumar A. Control of H1N1 influenza outbreak: A study conducted in a naval warship. J Mar Med Soc 2017;19:142-5

How to cite this URL:
Gupta A, Ray S, Tyagi R, Kumar A. Control of H1N1 influenza outbreak: A study conducted in a naval warship. J Mar Med Soc [serial online] 2017 [cited 2023 Feb 6];19:142-5. Available from: https://www.marinemedicalsociety.in/text.asp?2017/19/2/142/225284

  Introduction Top

H1N1 Influenza had presented as a public health emergency of international concern in 2009, with intangible scope, duration, and effect. There is a risk of rapid transmission of H1N1 Influenza in confined air-conditioned settings similar to the ships' environment.[1] This might cause high morbidity of the personnel on board, disrupt their daily activities, and leading to low crew morale, especially during a deployment. With a Secondary Attack Rates (SAR) as high as 45%[2] and strict isolation and quarantine almost impossible on board, controlling such an outbreak is extremely important for the medical team.[3]

Preventive measures such as handwashing and cough etiquettes are sine qua non, i.e., absolutely essential for the control of influenza infections in this scenario, and are required to be followed in letter and spirit.[4] The ships' crew is a healthy, young population and is usually not recommended vaccination as per the current protocols. Furthermore, there are availability and efficacy constraints of the new H1N1 strain vaccine, called A/Michigan/45/2015, which has replaced the 2009 strain A/California/7/2009 during this period.[5]

The aim of this study is to describe an H1N1 Influenza outbreak in a Naval Warship, with stated objectives of eliciting efficacy of the results of preventive measures, mainly in the form of handwashing, following cough etiquettes and active surveillance, in successful control of the outbreak.

  Materials and Methods Top

Data collection

Primary data were collected from the records available on board in the Warship and in the tertiary care hospital where the cases were treated. Secondary data were collected from the health returns sent to the concerned headquarters by the ship and the hospital. All cases of fever under investigation and upper and lower respiratory tract infections occurring among personnel on board in the Warship, starting from the index case, were listed. Details on demography, residence, date of onset of illness, clinical details, results of laboratory investigations, history of travel, and history of contact with positive case of Influenza (H1N1) were collected from these cases.

All these cases were referred to a tertiary care hospital for further management. Patients with positive laboratory tests were admitted to the H1N1 isolation ward of the hospital, based on their clinical condition and residential status (whether staying on board or in family accommodation).

Case definition

A suspected case of H1N1 Influenza is defined as a person with acute febrile respiratory illness (fever [>100.0°F]) with onset within 7 days of close contact with a person, who is a confirmed case of Influenza A (H1N1) 2009 virus infection, or within 7 days of travel to areas where there are one or more confirmed cases, or resides in a community where there are one or more confirmed cases of Influenza A (H1N1) 2009 cases. A confirmed case is defined as an individual with laboratory-confirmed new Influenza A (H1N1) virus infection by one or more of the following: real-time reverse transcriptase-polymerase chain reaction (RT-PCR), viral culture, or 4-fold rise in new Influenza A (H1N1) virus-specific neutralizing antibodies.[6],[7]

Laboratory investigation

Oropharyngeal swabs from all cases were subjected to RT-PCR for confirmation using the CDC/WHO testing protocol.[8]

Data analysis

Cases were classified according to the case definition; proportion of suspected and laboratory-confirmed cases, AR, and Case Fatality Rate (CFR) of the disease were calculated. To study the time and geographical distribution of cases, epidemic curve and area map were plotted, respectively. Active surveillance was continued for 14 days from the reporting of the last case to assess the effect of the employed control measures and detection of any fresh case.

Control measures initiated

The ship conformed to the international air-conditioning and ventilation standards as promulgated by the UK, Ministry of Defence Standard 2–102 (NES102).[3] The sickbay had only relative negative pressure with respect to ships' ventilation, along with a dedicated air filtration unit but no isolation compartment on board. Therefore, strict isolation and quarantine were not possible. Due to the potential for further dissemination of the disease among susceptible crew of the ship and due to the operational implications of such disease spread during sailing and deployment, all the suspected cases, whenever diagnosed, were disembarked.[1] Appropriate infection control measures and droplet precautions in the form of disinfection with 5% cresol used every 12 h were emphasized to be adhered to at all times. Strict handwashing was followed by all individuals along with the use of disposable tissue papers, cleaning of all door handles, ladder supports, and railings on board with alcohol-based sanitizers. Cough etiquette was advised to be followed as per the guidelines.[6] A surveillance system in the form of active case finding was followed by the health workers on board.

  Results Top

Over a 3-week period in June 2017, 21 patients sought treatment at sickbay of the ship. Mean age of the suspected cases was 26.71 years (with standard deviation ± 6.00 years) [Table 1]. The most common symptoms were sore throat, cough, and fever with only two cases having gastrointestinal symptoms of vomiting.
Table 1: Distribution of cases according to their general characteristics

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Of 21 clinically suspected cases, swabs of 14 cases were positive for influenza A (H1N1). Of two confirmed cases detected on 08 June, one gave a positive history of coming in contact with a confirmed case of H1N1. He was taken as an index case in this outbreak. Nine patients were admitted to the H1N1 isolation ward of the hospital, based on their clinical condition and residential status. Of the nine cases admitted, two developed complications, which were managed promptly.

The Attributable Risk (AR) of H1N1 influenza during the 14-day period was 4.83%. The epidemic curve was prepared and is shown in [Figure 1]. Cases were evenly distributed across all areas of the ship and among all ranks (including officers and sailors), with no specific post or compartment showing an exceptionally high AR.
Figure 1: Epidemic curve of time distribution of cases.

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All cases were prescribed tablet Oseltamivir 75 mg twice a day as per the standard protocol.[9] There were no fatalities due to the disease. The Case Fatality Rate (CFR) of the disease in the present outbreak was nil.

  Discussion Top

Control of H1N1 Influenza outbreak in a confined ships' environment is a challenging task. Effective preventive measures were instituted on a war footing, and the outbreak was controlled within 14 days. It predominantly affected the young and middle-aged individuals as has been brought out in similar studies on the disease.[10] The time of occurrence corresponded to the peak season of Influenza transmission in India.[11] Fever, cough, and sore throat have been most commonly elicited symptoms during H1N1 Influenza outbreaks [12] and a similar situation was found in this study. Majority of the cases responded well to antiviral treatment and attained disease-free status without developing any complications. Nil CFR observed in this outbreak was comparable to the estimates of 0.004%–1.5% reported from other countries.[13]

Disease spread during H1N1 Influenza outbreaks can reach ARs as high as 51%,[14] and appropriate prevention and control measures are essential to restrict the spread. The study done on board, similar to this, was an outbreak of Influenza A (H3N2) that occurred aboard a US Navy ship and had an AR of 42%.[15] Low attack of 4.835% in this study cannot be attributed solely to the natural course of the outbreak and is definitive indicator that interventions had a substantial beneficial effect. The outbreak emphasizes the crucial role of continuous surveillance for H1N1 Influenza in the afloat settings as rapid detection is a major factor in success of control measures. Similar control measures were observed to be employed during a H1N1 Influenza outbreak on a cruise ship.[16]

The explosive pattern of this outbreak, as demonstrated by the sudden increase in the number of cases within a week of first case, a background of increase in number of cases in the environment, and a high index of suspicion, enabled rapid detection and initiation of prompt investigation and control measures. With the data available, it was not possible to quantify the effects of the control measures and hence, no particular control measure was identified which made a significant difference in controlling the outbreak.

Epidemic curve depicts a point source and not a person-to-person transmission pattern, which is consistent with H1N1 Influenza. Person-to-person transmission in this study was effectively terminated with the active case finding and disembarking of the suspected individuals from the ship. Therefore, because of aggressive control measures, the outbreak had a pattern of “point source” epidemic in this study.

The role of immunization against H1N1 Influenza in a Naval afloat platform is debatable as the workforce deployed on board is relatively young. Moreover, the efficacy of the vaccine with the circulating strain is questionable.[5] Furthermore, if the AR is <7.6% (which is achievable with simple public health interventions as brought out in text above), then vaccination is not cost-effective in low-risk subgroups.[17]

  Conclusion Top

In confined afloat settings, public health measures of active case finding, strict isolation, and adherence to hand hygiene, following cough etiquettes and disinfection enhancement, can effectively mitigate the outbreak. Vaccination might not have a role to play if preventive measures are instituted in time and effectively. Furthermore, hospital support in diagnosis and prompt management with Oseltamivir help in the early management of H1N1 influenza and prevent complications.


We would like to acknowledge the Fleet Medical Officer, Officerin Charge, Station Health Organisation, Head of Department, Microbiology, INHS Asvini for their support.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

WHO Interim technical advice for case management of pandemic (H1N1) 2009 on ships, 13 November 2009. Available from: www.who.int/csr/resources/publications/swineflu/guidance_ships/en/. [Last accessed on 2017 Oct 08].   Back to cited text no. 1
Makras P, Alexiou-Daniel S, Antoniadis A, Hatzigeorgiou D. Outbreak of meningococcal disease after an influenza B epidemic at a Hellenic Air Force Recruit Training Center. Clin Infect Dis 2001;33:e48-50.  Back to cited text no. 2
Ministry of Defence. Defence Standard 02-102 (NES 102). Issue 2 Publication Date 8 September, 2000. Available from: http://www.ftp://ftp.iks-jena.de/mitarb/lutz/standards/dstan/02/102/01000200.pdf. [Last accessed on 2017 Oct 08].  Back to cited text no. 3
Shruti G, Sougat R. Is cough etiquette more useful than handwashing in prevention of swine flu in India? BMJ 2015;350:H1097.  Back to cited text no. 4
Recommended Composition of Influenza Virus Vaccines for Use in the 2017-2018 Northern Hemisphere Influenza Season. Available from: http://www.who.int/influenza/vaccines/virus/recommendations/201703_recommendation.pdf?ua=1. [Last accessed on 2017 Oct 06].  Back to cited text no. 5
Government of India. Guidelines of Swine flu (Influenza A H1N1), Ministry of Health and Family Welfare, New Delhi; 2010.  Back to cited text no. 6
World Health Organization (WHO). A Practical Guide to Harmonizing Virological and Epidemiological Influenza Surveillance; 2008. Available from: http://www.wpro.who.int/entity/emerging_diseases/documents/GuideToHarmonizingInfluenzaSurveillance-revised2302/enlindex.html. [Last accessed on 2017 Oct 07].  Back to cited text no. 7
World Health Organization. CDC Protocol of Real-time RT-PCR for Influenza A (H1N1). Available from: http://www.who.int/csr/resources/publications/swineflu/CDCRealtimeRTPCR_SwineH1Assay-2009_20090430.pdf. [Last accessed on 2017 Oct 07].  Back to cited text no. 8
WHO. Clinical Management of Human Infection with Pandemic (H1N1) 2009. Revised Guidelines; November, 2009.  Back to cited text no. 9
Altayep KM, Ahmed HG, A Tallaa AT, Alzayed AS, Alshammari AJ, Ali Talla AT, et al. Epidemiology and clinical complication patterns of influenza A (H1N1 virus) in Northern Saudi Arabia. Infect Dis Rep 2017;9:6930.  Back to cited text no. 10
Agrawal AS, Sarkar M, Chakrabarti S, Rajendran K, Kaur H, Mishra AC, et al. Comparative evaluation of real-time PCR and conventional RT-PCR during a 2 year surveillance for influenza and respiratory syncytial virus among children with acute respiratory infections in Kolkata, India, reveals a distinct seasonality of infection. J Med Microbiol 2009;58:1616-22.  Back to cited text no. 11
BinSaeed AA. Characteristics of pandemic influenza A (H1N1) infection in patients presenting to a university hospital in Riyadh, Saudi Arabia. Ann Saudi Med 2010;30:59-62.  Back to cited text no. 12
[PUBMED]  [Full text]  
Writing Committee of the WHO Consultation on Clinical Aspects of Pandemic (H1N1) 2009 Influenza, Bautista E, Chotpitayasunondh T, Gao Z, Harper SA, Shaw M, et al. Clinical aspects of pandemic 2009 influenza A (H1N1) virus infection. N Engl J Med 2010;362:1708-19.  Back to cited text no. 13
Glatman-Freedman A, Portelli I, Jacobs SK, Mathew JI, Slutzman JE, Goldfrank LR, et al. Attack rates assessment of the 2009 pandemic H1N1 influenza A in children and their contacts: A systematic review and meta-analysis. PLoS One 2012;7:e50228.  Back to cited text no. 14
Earhart KC, Beadle C, Miller LK, Pruss MW, Gray GC, Ledbetter EK, et al. Outbreak of influenza in highly vaccinated crew of U.S. Navy ship. Emerg Infect Dis 2001;7:463-5.  Back to cited text no. 15
Ward KA, Armstrong P, McAnulty JM, Iwasenko JM, Dwyer DE. Outbreaks of pandemic (H1N1) 2009 and seasonal influenza A (H3N2) on cruise ship. Emerg Infect Dis 2010;16:1731-7.  Back to cited text no. 16
Prosser LA, Lavelle TA, Fiore AE, Bridges CB, Reed C, Jain S, et al. Cost-effectiveness of 2009 pandemic influenza A (H1N1) vaccination in the United States. PLoS One 2011;6:e22308.  Back to cited text no. 17


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