AnovelinfluenzaA(H1N1)virusresultingfromtriplere-assortmentemergedinMexicoandtheUSAin 20091. In late April 2009, WHO declared thatthe emergence of this virus represented a ‘publichealth emergency of international concern’ and onJune 2009, raised the phase of pandemic alert to

AnoutbreakofpandemicinfluenzaA(H1N1)inKolkata, WestBengal,India,2010

DilipK.Biswas*,**,PrabhdeepKaur**,ManojMurhekar**&RamaBhunia*,**

*Directorate of Health Services, Government of West Bengal & **Field Epidemiology Training Programme, National Institute of Epidemiology (ICMR), Chennai, India

ReceivedMarch29,2011

Background & objectives: An increased number of cases with influenza like illness (ILI) were reported in Greater Kolkata Metropolitan Area (GKMA) during July and August 2010. We investigated these cases to confirm the outbreak, describe the distribution of patients and propose control measures.Methods: A suspected case of influenza like illness (ILI) was defined as acute onset of fever (>38oC) with cough or sore throat and a confirmed case as ILI case with throat swab positive for influenza A (H1N1) on RT-PCR. The demographic and clinical details were collected from patients attending the swine flu OPD of Infectious Disease Hospital, Kolkata, during July 5 to August 16, 2010.Results: Overall 440 patients with ILI attended the swine flu OPD of Infectious Disease and Bengal General hospital during the study period, of which 129 were positive for influenza A (H1N1). Four patients died (case fatality ratio: 0.90%). Besides fever, common symptoms included cough (73%), running nose (54%), sore throat (43%), respiratory distress (25%) and diarrhoea (4%). Forty seven (11%) patients (including the four who died) had co-morbidities. The outbreak started on July 10, peaked on July 24 and subsided by August 14, 2010. A total of 372 (85%) patients were from GKMA. Majority (n=168, 45%) of the cases from GKMA were from 6 boroughs of Kolkata Municipal Areas.Interpretation & conclusions: An outbreak of influenza A (H1N1) occurred in Kolkata predominantly affecting young and middle aged population. State health authorities implemented several interventions to limit the outbreak including training of health care providers in case management and infection control, vaccination of health care workers, creation of isolation wards and administration of oseltamivir to ILI patients, and community health education about social distance and personal hygiene measures.

Key wordsA(H1N1)-pandemicinfluenza-swineflu

six, indicating the emergence of the new influenzapandemic. The H1N1 virus had spread with greatspeedtoall thecontinentsandcausedconsiderablehumansufferingandanadverseimpactonthehealthservicesandtheeconomy.Worldwide,214countriesandoverseasterritoriesorcommunitieshadreported

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laboratoryconfirmedcasesofpandemicinfluenzaA(H1N1)includingatleast18,449deathsasonAugust20102.

In India, the first confirmed case of pandemicinfluenzaA(H1N1)wasreportedinHyderabadonMay16,20093andbyJuly2010,atotalof34,669laboratoryconfirmedcasesincluding1,692deathswerereported4. DuringJune2009toJuly2010,atotalof2971nasal/throat swabs from suspected influenza patients weretested from the eight States (West Bengal, Bihar,Orissa, Meghalaya, Mizoram, Tripura andAndamanandNicobarislands).Amongthese,382(12.9%)werepositivefortheinfluenzaAand103(3.5%)forinfluenzaB.About75percentoftheinfluenzaApositivesweresub-typed as pandemic H1N1 (pH1N1) while theremaining were due to seasonal H1N1 and H3N25. West Bengal reported 265 cases of pandemic H1N1duringthisperiod.OnlyonecasewasreportedfromtheStateduringJanuary toJune20105.SinceJuly2010,therewereincreasednumberofcasesofinfluenzalikeillness(ILI)reportedintheKolkatametropolitanarea.We conducted an outbreak investigation to confirmtheaetiology,describethedistributionofcase-patientsby time, place and person, and recommend controlmeasures.

Material & Methods

Case definition:Acaseof influenza like illness (ILI)wasdefinedasanacuteonsetof fever(>38oC)withorwithoutcoughorsorethroatintheabsenceofanyother diagnosis6. A person with ILI with laboratoryconfirmationforinfluenzaA(H1N1)onathroatswabby real time reverse transcriptase polymerase chainreaction(RT-PCR)wasconsideredasconfirmedcaseofpandemicinfluenza(H1N1)7.Allthepatientsmeetingthe above case definitions and attending the swineflu OPD of Infectious Disease and Bengal General(ID&BG)hospital,Kolkata,wereincludedinthestudy.Following thedeathof one confirmedcaseofH1N1infection, the Government of West Bengal made itmandatorytoreferallILIcasesfromprivatehospitals,medicalcollegehospitalstoID&BGHospital,Kolkata,forlaboratoryconfirmation.

Data collection:Atthetimeofcollectingthroatswabsfor laboratory confirmation, complete address of thesuspectedpatientswascollected.PatientswithpositivelaboratorytestsforpandemicH1N1wereencouragedto get admission in the swine flu ward of ID&BGHospital for treatment. Patients (or their relatives)admitted inothernursinghomeswerealsocontacted

using the addresses provided by them at the time oflaboratorytesting.

AteamofsevenhealthworkerscollectedinformationfromallthecasesofILIaboutthedemographicdetails,residence, date of onset of illness, clinical details,results of laboratory investigations, history of travelwithinandoutsidethecountryandhistoryofcontactwithpositivecaseofinfluenza(H1N1).

Laboratory investigation:ThroatswabswerecollectedfromalltheILIpatientsinsterileviraltransportmediumandtransportedundercoldchaintotheNationalInstituteofCholeraandEntericDiseases,(ICMR),Kolkata,theStatereferrallaboratory,forRT-PCRusingtheCDC/WHOtestingprotocolforinfluenzaA(H1N1)8.

Data analysis: We calculated the proportion ofsuspectedandlaboratoryconfirmedcasesbyagegroupsand gender.The epidemic curvewas drawn to studythedistributionof casesby timeandan areamap toknowthegeographicaldistributionofallthecases.Fordescribing the distribution by geographic areas, onlythosepatientsresidinginGreaterKolkataMetropolitanAreas(GKMA)wereconsideredandcensuspopulationwas used as denominator to calculate the attackrates. Greater Kolkata MetropolitanAreas (GKMA)comprise of (i) Kolkata Metropolitan Corporationarea(KMC),(ii)HowrahMunicipalCorporationareas(HMC), and (iii) three adjacent municipalities fromdistrictNadia,20adjacentmunicipalities fromNorth24Parganasdistrict,nineadjacentmunicipalitiesfromHooghlydistrictandfiveadjacentmunicipalitiesfromdistrict South 24 Parganas. There are 15 boroughs(administrativeunits)inKMCandfiveinHMCarea.

Results & Discussion

Between July 5 andAugust 16, 2010, a total of893 patients attended the swine fluOPD of ID&BGHospital, Kolkata (average 29 patients per day). Ofthem,440(49%)hadsymptomsofILIandtheirthroatswabsweresenttolaboratoryinvestigations.Ofthese440ILIthroatswabs149(33.9%)werereferredfromtheprivatenursinghomesormedicalcollegehospitals.InfluenzaA(H1N1)virus infectionwasconfirmedin129 (29%) patients (Table I). Of the 129 laboratoryconfirmed patients, 96 (74%) were admitted in theID&BG Hospital, 30 (23%) in the private nursinghomes/medicalcollegehospitals,whilethreepatientsremainedisolatedintheirhouses(TableI).

Thecommonestsymptomsincludedfever(100%),cough(73%),runningnose(54%),sorethroat(43%),

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respiratory distress (25%) and diarrhoea (4%). Fortyseven patients (11%) had associated co-morbidconditions.Thecommonco-morbiditieswerechronicobstructive pulmonary disease (COPD) (29.8%),cardiovasculardisease(21.3%),liver(10.6%),kidney(10.6%) disease and 2 per cent had diabetes. Allexceptfourpatientsrecoveredwith5-7daycourseofoseltamivir,antibioticsandparacetamol(Casefatalityratio=0.90%).Ofthefourpatientswhodied,threewereaged>50yrwhileonewas13yrold.Allhadassociatedco-morbid conditions such as COPD, chronic renalfailure,heartfailureandhepatitis.

Most of the suspected (n=269, 61.1%) andlaboratory confirmed (n=77, 59.7%) cases were in

theagegroupof15-49yr(TableII).ILIcasesstartedoccurringfromJuly10,2010withseveralpeaksintheepidemiccurveandsubsidedonAugust14,2010(Fig.1). Of the 440 cases, 372 (85%)were fromGreaterKolkata Metropolitan areas, while 68 (15%) werefrom neighbouring districts and States. In GKMA,caseswerereportedfromalltheboroughsoftheKMC(exceptboroughnumber2)andoneboroughinHMC.Six boroughs in KMC (Number 3, 5, 6, 10, 12 and14) accounted for 45 per cent (168/372) caseswhileBidhannagar and Dum Dum municipality togetheraccounted20percentofthecases(Fig.2).Sixtythree(14%)patientsgavehistoryofcontactwithlaboratoryconfirmedcasesofinfluenzaA(H1N1)inthepreviousweek,while18(4%)hadarecenttravelhistory(eitherabroadorotherStatesofthecountry)(TableI).

In India, the earlier H1N1 outbreaks have beenreported in institutional settings9,10. The outbreak inKolkataoccurred in theurbanpopulationwith abouthalfofthecasesbeingreportedfromsixboroughsinKMC,suggestingthepossibilityofclosecontactwithcases.Theoutbreakpredominantlyaffectedtheyoungandmiddleagedindividualsandthetimeofoccurrencecorresponded to the peak season of influenzatransmission in India11,12.Majority of the caseswereuncomplicated and responded to anti-viral treatment.The case fatality ratio of 0.90 per cent observed inthisoutbreakwascomparabletotheCFRestimatesof0.004-1.5percentreportedfromothercountries13.

InAugust2010,WHOdeclaredthepost-pandemicphase of the H1N1. During this phase, cases andoutbreaks due to the H1N1 (2009) virus would

Table I. Distributionofinfluenzalikeillness(ILI)casesduringtheH1N1outbreak,GreaterKolkataMetropolitanAreas,WestBengal,India2010Characteristics n/N %Laboratoryinvestigations NumberofILIcasessentforthroatswabforH1N1 440/893 49

NumberofILIcasesreferredfromprivatenursinghome/medicalcollegeforlaboratoryinvestigations

149/440 30

Numberoflaboratoryconfirmedcases 129/440 29Placeofhospitalizationoflaboratorypositivecase-patients

ID&BGhospital,Kolkata 96/129 74Nursinghomes/medicalcolleges 30/129 23Selfquarantineathome 3/129 2.3

Co-morbidity Morbiddiseaseconditions(lung,heart,liverandkidneydisease) 47/440 11Urban/Rural Urban 372 85

Rural 68 15Epidemiologicalfindings Recenttravelhistory 18 4

HistoryofcontactofH1N1positivecases 63 14

Table II. Proportion of suspected and confirmed cases ofinfluenzabyagegroupandgender,WestBengal,India2010Age Suspectedcases

(n=440)Laboratoryconfirmed

cases(n=129)Number % Number %

Age(yr)1-4 36 8.18 9 7.05-14 48 10.9 16 12.415-24 87 19.8 29 22.525-34 104 23.6 29 22.535-49 78 17.7 19 14.750-60 37 8.4 15 11.6>60 50 11.4 12 9.3

GenderMale 252 57.3 70 54.26Female 188 42.7 59 45.73

BISWASet al:INFLUENZAA(H1N1)OUTBREAK,KOLKATA,WESTBENGAL 531

Fig. 2. Attackrateper100,000populationofILIbyboroughofKolkataMetropolitanCorporation,HowrahMunicipalCorporationandmunicipalityareasofGreaterKolkataMetropolitanAreas,WestBengal,India,2010(Mapnottoscale).

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Fig. 1. EpidemiccurveofswinefluoutbreakatGreaterKolkataMetropolitanArea,WestBengal,India,2010.

July 2010 August 2010

5 8 10 12 14 16 18 20 22 24 26 28 30 1 3 5 7 9 11 13 15

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continue tooccur.Earlydetectionof theseoutbreaksandimplementationofcontrolmeasuresareessentialto limit the transmission. The West Bengal StateHealthDepartmentinitiatedseveralcontrolmeasures.The IB& BGHospital, Kolkata, was designated asthenodalhospitalfortreatmentofcaseswithaswinefluwardconsistingof35beds.Facilitiesforisolationandtreatmentwerealsoestablishedat thedesignatednursing homes, medical colleges as well as district

hospitals. In Kolkata alone, a total 310 isolationbeds in 25 health institutions were made ready forsuch cases. These health facilities were suppliedwithadequatequantitiesofantivirals.All thenursingpersonnel,doctors,paramedicalstaffsengaged in theswinefluwardwerevaccinatedwithswinefluvaccine.GovernmentofWestBengalalsomadeitmandatoryforalltheprivatenursinghomestoreferthecasesofILItoID&BGHospitalforlaboratorytestofH1N1virus.

ThelaboratoryconfirmedILIpatientswereencouragedtogetadmissioninID&BGHospital,Kolkata,privatenursinghomeormedicalcollegehospitals.Fivedaystreatmentwithosteltamivir(Tamiflu)wasadministeredtoallthelaboratoryconfirmedpatientsaswellastheirclosefamilycontacts.Extensiveinformation,educationandcommunication(IEC)activitiesweredoneinthecommunitiestoeducatethepeopleaboutpreventionofinfluenza.

Acknowledgment The authors acknowledge Drs Akhil Bandhu Biswas, AsitKumar Biswas and Sukanta Biswas from Directorate of HealthServices,GovernmentofWestBengal,India;themedicalofficersandpara-medicalstaffofID&BGHospital,Kolkata,WestBengal,and Director, NICED, staff of NICED, Kolkata, for their co-operationandhelp.

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Reprint requests:DrDilipK.Biswas,DeputyChiefMedicalOfficerofHealth-II,PurbaMedinipur721636,WestBengal,India e-mail:dilipbiswas29@gmail.com

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