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Enhanced surveillance

The outbreak of acute respiratory infections in La Glo-ria, Veracruz (population 2155) was characterized by alarge number of cases (616 inhabitants; 28.5% of thepopulation) reported during 5 March10 April 2009.This outbreak was probably of mixed cause: subsequenttesting of respiratory specimens collected at the timeidentified 3 patients as positive for different seasonalinfluenza virus strains (2 influenza A (H3N2) and 1 in-fluenza B) and 1 patient as positive for new influenzaA (H1N1) virus with an adenovirus coinfection. A largemajority of the respiratory illnesses from this outbreakremain undiagnosed. No severe cases or deaths wereobserved.

During March and April 2009, clusters of rapidly pro-gressive severe pneumonia were identified in MexicoCity, San Luis Potosi and other cities. These included47 cases and 12 deaths; 4 of the deaths were positivefor new influenza A (H1N1) virus infection. In responseto the La Gloria outbreak and the pneumonia clusters,

the Mexico national committees of epidemiologicalsurveillance and emerging infectious diseases releasedan epidemiological alert on 17 April to enhance na-tional surveillance for acute respiratory infections andsevere pneumonia. Active case-finding was imple-mented in hospitals throughout the country, includingdaily zero-reporting (requiring facilities and jurisdic-tions to report even if no suspected cases had beenidentified), and monitoring of news media and othersources. The Ministry of Health also initiated investi-gations of outbreaks throughout the country, with theassistance of the WHO Global Outbreak and Alert Re-sponse Network, coordinated by the Pan American

Health Organization.

During 1819 April 2009, a survey conducted in 23 hos-pitals in Mexico City indicated increased pneumonia-related hospital admissions since 10 April, particularlyamong young adults. On 21 April, respiratory specimenscollected as a result of these enhanced surveillance ac-tivities were sent to the National Microbiology Labora-tory of the Public Health Agency of Canada and to theInfluenza Division at the United States Centers for Dis-ease Control and Prevention (CDC). During 2224 April,both laboratories identified new influenza A (H1N1) vi-rus infection in specimens collected from Mexican pa-

tients. The Directorate General of Epidemiology (DGE)established an Internet-based reporting platform to col-lect case-based epidemiological information and a dailyepidemiological bulletin to disseminate the results ofongoing investigations and recommendations fromDGE. This bulletin was first released on 26 April 2009.

In May 2009, the Ministry of Health of Mexico revisedits case definition of a suspected case of new influenzaA (H1N1) virus infection. The initial definition, whichincluded any hospitalized patient with severe acute re-spiratory illness, was expanded on 1 May to include anyperson with acute respiratory illness (defined as fever

and either sore throat or cough). On 11 May, this defini-tion was refined to include any person with fever, cough,and headache plus at least 1 of the following symptoms:

Surveillance renforce

La flambe dinfections respiratoires aigus survenue LaGloria, Veracruz (2155 habitants), a t caractrise par ungrand nombre de cas (616 habitants; 28,5% de la population)signals entre le 5 mars et le 10 avril 2009. Cette flambe avaitprobablement plusieurs causes: lanalyse ultrieure des chan-tillons respiratoires prlevs lpoque a permis didentifier3 patients positifs pour des souches diffrentes de virus de lagrippe saisonnire (2 pour le virus grippal A (H3N2) et 1 pourle virus grippal B) et 1 patient positif pour le nouveau virusgrippal A (H1N1) avec co-infection par un adnovirus. Pour unegrande majorit de maladies respiratoires observes lors decette flambe, le diagnostic na pas t pos. Aucun cas graveni dcs nont t observs.

En mars et avril 2009, des grappes de cas de pneumonie gravedvolution rapide ont t identifies Mexico, San Luis Potosiet dans dautres villes. On a ainsi dnombr 47 cas et 12 dcs.Quatre des sujets dcds taient positifs pour le nouveau virusgrippal A (H1N1). En raction la flambe survenue La Gloriaet aux grappes de cas de pneumonie, les comits nationaux

mexicains de surveillance pidmiologique et des maladiesinfectieuses mergentes ont publi, le 17 avril, une alerte pid-miologique visant renforcer la surveillance nationale desinfections respiratoires aigus et de la pneumonie svre. Undpistage actif des cas a t mis en place dans les hpitaux delensemble du pays, comprenant la notification quotidienne delabsence de cas (les tablissements et entits territoriales tanttenus de faire rapport mme si aucun cas prsum na t iden-tifi), et une surveillance des mdias et dautres sources. LeMinistre de la Sant a galement entam linvestigation desflambes partout dans le pays avec lassistance du rseaumondial OMS dalerte et daction en cas dpidmie, coordon-ne par lOrganisation panamricaine de la Sant.

Les 18 et 19 avril 2009, une enqute effectue dans 23 hpitauxde Mexico a fait apparatre une augmentation des hospitalisa-tions lies la pneumonie depuis le 10 avril, en particulierparmi les jeunes adultes. Le 21 avril, des chantillons respira-toires prlevs en raison de ces activits de surveillance renfor-ces ont t envoys au Laboratoire national de microbiologiede lAgence de Sant publique du Canada ainsi qu la Divisionde la Grippe des Centers for Disease Control and Prevention desEtats-Unis (CDC). Entre le 22 et le 24 avril, les 2 laboratoiresont identifi le nouveau virus grippal A (H1N1) dans les chan-tillons recueillis sur des patients mexicains. La Direction gn-

rale de lEpidmiologie (DGE) a mis en place une centrale denotification sur Internet charge de recueillir les informationspidmiologiques sur la base des cas observs et de diffuser unbulletin pidmiologique quotidien afin de communiquer lesrsultats des investigations en cours et les recommandations dela DGE. Ce bulletin a t publi pour la premire fois le 26 avril2009.

En mai 2009, le Ministre de la Sant mexicain a revu sa dfi-nition du cas prsum dinfection par le nouveau virus grip-pal A (H1N1). La dfinition initiale, qui faisait rfrence toutpatient hospitalis pour maladie respiratoire aigu svre, a tlargie au 1er mai toute personne prsentant une maladierespiratoire aigu (dfinie comme une fivre accompagne soit

de mal de gorge soit de toux). Le 11 mai, cette dfinition a taffine afin de concerner toute personne prsentant fivre, touxet cphales, plus au moins lun des symptmes suivants:

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rhinorrhoea, coryza, arthralgia, myalgia, prostration,sore throat, chest pain, abdominal pain or nasal conges-tion. In children aged

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Table1 Distribution by age of suspected, tested and laboratory-confirmed cases of new influenza A (H1N1) virus infection and laboratory-

confirmed deaths, Mexico, MarchMay 2009

Tableau 1 Rpartition en fonction de lge des cas prsums, tests et confirms en laboratoire de nouvelle grippe A (H1N1) et des dcs

au Mexique, mars-mai 2009

Age (years) Age

(annes)

Total no. of suspected

cases Nombre total

de cas prsums

No. of cases tested

Nombre de cas tests

Number of laboratory-

confirmed positive

cases (% of

confirmedcases)a Nombre de

cas positifs confirms

en laboratoire (% de

cas confirms)a

Positive cases/

100 000 population

Cas positifs/

100 000 habitants

No. of deaths among

laboratory-confirmed

cases (% of confirmed

deaths) Nombre dedcs parmi les cas

confirms en labora-

toire (% de

dcs confirms)

2009 populationb

Population 2009b

04 6 428 3 520 695 (13.2) 7.26 5 (5.2) 9 578 579

514 7 742 4 229 1 517 (28.7) 7.11 7 (7.2) 21 327 734

1529 11 568 7 591 1 704 (32.3) 5.83 26 (26.8) 29 221 168

3059 12 687 8 507 1 251 (23.7) 3.26 54 (55.7) 38 330 279

60 2 249 1 016 112 (2.1) 1.23 5 (5.2) 9 092 937

Missing Donnes

manquantes

1 324 264 58

Total 41 998 25 127 5 337 (100.0) 4.96 97 (100.0) 107 550 697

a Source: Direccin General Adjunta de Epidemiologa (Directorate General of Epidemiology). Boletn Diario, 2009, 29 May, No. 29. Source: Direccin General Adjunta de Epidemiologa(Direction gnrale de lEpidmiologie). Boletn Diario, 2009, 29 mai, No 29.

b Source: Consejo Nacional de Poblacin (CONAPO); National Council of Population; see http://www.conapo.gob.mx/index.php?option=com_content&view=article&id=36&Itemid=234. Source: Consejo Nacional de Poblacin (CONAPO); Conseil national de la Population; voir http://www.conapo.gob.mx/index.php?option=com_content&view=article&id=36&Itemid=234.

Fig. 1 Number of laboratory-confirmed cases of new influenza A (H1N1) virus infection and laboratory-confirmed deaths, by state,

Mexico, March-May 2009

Fig. 1 Nombre de cas confirms en laboratoire de nouvelle grippe A (H1N1) et de dcs confirms en laboratoire, par tat, Mexique,

mars mai 2009

0

500

1000

1500

2000

Aguascalientes

BajaCalifornia

BajaCaliforniaSur

Campeche

Chihuahua

Chiapas

Coahuila

Colima

DistritoFederal

Durango

Guerrero

Guanajuato

Hidalgo

Jalisco

Mexico

Michoacan

Morelos

Nayarit

NuevoLeon

Oaxaca

Puebla

Queretaro

QuintanaRoo

Sinaloa

SanLuisPotosi

Sonora

Tabasco

Tamaulipas

Tlaxcala

Veracruz

Yucatan

Zacatecas

M

issingunkoown

No.

oflaboratory-confirmedcasesanddeathsNombredecas

confirmsenla

boratoireetdedcs

Laboratory-confirmed cases Cas

confirms en laboratoire

Deaths Dcs

State Etat

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and parents screened children at school entrances to

determine whether they had fever or respiratory symp-toms. The ministries of education and health recom-mended the closure of classrooms where >2 childrenpresented respiratory symptoms and of schools with illchildren in >2 classrooms. On the first day of this strat-egy, 91 357 children were detected as symptomatic. Thisscreening practice was suspended on 23 May.

Reported by: Office of the Secretary of Health, Ministryof Health, Mexico (Secretara de Salud, Mxico, http://portal.salud.gob.mx); Directorate General of Epidemiol-ogy, Ministry of Health (Direccin General Adjuntade Epidemiologa, http://www.dgepi.salud.gob.mx);

National Institutes for Epidemiological Reference andDiagnostics (Institutos de Diagnstico y ReferenciaEpidemiolgicos; http://www.cenavece.salud.gob.mx/indre/); National Institute of Public Health, Mexico(Instituto Nacional de Sald Publica, http://www.insp.mx/); Pan American Health Organization/World HealthOrganization (http://new.paho.org/hq/); Public HealthAgency of Canada (http://www.phac-aspc.gc.ca/);National Institute for Respiratory Diseases (InstitutoNacional de Enfermedades Respiratorias, http://www.iner.salud.gob.mx); National Center for Preparedness,Detection, and Control of Infectious Diseases (http://www.cdc.gov/ncpdcid/); Epidemic Intelligence Service

(http://www.cdc.gov/eis/index.html).Editorial note. Trends in case counts in Mexico suggestthat new influenza A (H1N1) virus activity is now

0

50

100

150

200

250

300

350

400

11.

3.

09

18.

3.

09

25.

3.

09

1.

4.

09

8.

4.

09

15.

4.

09

22.

4.

09

29.

4.

09

6.

5.

09

13.

5.

09

20.

5.

09

27.

5.

09

No.

oflaboratory

-confirmedcasesNombredecasconfirmsenlaboratoire

Date (dd-mm-yy) Date (jj-mm-aa)

Fig. 2 Number of laboratory-confirmed cases of new influenza A (H1N1) virus infection, by date of onset of illness, Mexico, March

May 2009

Fig. 2 Nombre de cas confirms en laboratoire de nouvelle grippe A (H1N1) et nombre de dcs confirms en laboratoire, par date

dapparition de la maladie, Mexique, mars mai 2009

de parents examinaient les enfants lentre de lcole pour vri-

fier quils ne prsentaient ni fivre ni symptmes respiratoires.Les Ministres de lEducation et de la Sant ont recommand lafermeture des classes o au moins 2 enfants prsentaient dessymptmes respiratoires et des coles comptant des enfantsmalades dans >2 classes ou plus. Le premier jour de mise enplace de cette stratgie, on a dcel des symptmes chez91 357 enfants. Cette pratique a t suspendue le 23 mai.

Daprs: Bureau du Secrtaire de la Sant, Ministre de la Sant,Mexique (Secretara de Salud, Mxico, http://portal.salud.gob.mx); Direction gnrale dEpidmiologie, Ministre de la Sant(Direccin General Adjunta de Epidemiologa, http://www.dgepi.salud.gob.mx); Instituts de Diagnostic et de Rfrence pid-

miologiques (Institutos de Diagnstico y Referencia Epidemio-lgicos, http://www.cenavece.salud.gob.mx/indre/); Institutnational de Sant publique, Mexique (Instituto Nacional deSald Publica, http://www.insp.mx/); Organisation panamri-caine de la Sant et Organisation mondiale de la Sant (http://new.paho.org/hq/); Agence de Sant publique du Canada (http://www.phac-aspc.gc.ca/); Institut national des Maladies respira-toires (Instituto Nacional de Enfermedades Respiratorias, http://www.iner.salud.gob.mx); National Center for Preparedness,Detection, and Control of Infectious Diseases (http://www.cdc.gov/ncpdcid/); Epidemic Intelligence Service (http://www.cdc.gov/eis/index.html).

Note de la rdaction. Lvolution du nombre de cas au Mexiquelaisse supposer que lactivit du nouveau virus grippal A (H1N1)

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decreasing, although localized transmission continuesto occur. The epidemic curve of laboratory-confirmedcases remains incomplete because of a backlog of un-tested specimens. However, data regarding suspectedcases3 also indicate a peak in late April 2009, and delaysfrom case identification to reporting have decreased toa median of

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been occasionally reported outside of the usual influ-enza season.9 However, an unprecedented number ofsuch off-season outbreaks are now occurring that alsoinvolve extension into the community, as demonstratedby confirmed illness among travellers with no knownepidemiological link to focal outbreaks. Similar patternsof off-season outbreaks have been observed with theemergence and sustained transmission of other strainsof new influenza A virus infection among humans.10

The recent introduction of new influenza A H1N1virus into several countries in the southern hemi-sphere at the beginning of their influenza season, andthe presumed susceptibility among much of the pop-ulation to this new virus, suggest that new influ-enza A (H1N1) virus might become a dominant cir-culating virus in the southern hemisphere over thecoming months. The Government of Mexico contin-ues to coordinate a national response, engage part-ners, increase surge capacity and implement mitiga-tion measures to slow the spread of transmission

with new influenza A (H1N1) virus infection. Inves-tigations are ongoing to monitor virus circulationand to evaluate the impact of mitigation strategiesthat might help guide prevention and control strate-gies in Mexico and worldwide.

As of 1 June 2009, 64 countries worldwide had reportedat least 1 laboratory-confirmed case of human infectionwith new influenza A (H1N1) virus. Because many ofthese infected individuals may have travelled while be-ing asymptomatic, pre-departure screening has limita-tions in controlling export of the virus. However, raisedawareness in travellers has proven efficacious inprompting spontaneous reporting of influenza-like ill-ness by travellers to health authorities at points of en-try.

9 Kohn MA et al. Three summertime outbreaks of influenza type A. Journal of Infec-tious Diseases, 1995,172:246249.

10Taubenberger JK, Morens DM. 1918 influenza: the mother of all pandemics. Emer-ging Infectious Diseases, 2006,12:1522 (available at http://www.cdc.gov/ncidod/eid/vol12no01/05-0979.htm; accessed June 2009).

9 Kohn MA et al. Three summertime outbreaks of influenza type A. Journal of Infectious Diseases,1995,172:246249.

10 Taubenberger JK, Morens DM. 1918 influenza: the mother of all pandemics. Emerging InfectiousDiseases, 2006,12:1522 (disponible sur http://www.cdc.gov/ncidod/eid/vol12no01/05-0979.htm; consult en juin 2009).

tuelle.9 Toutefois, on assiste maintenant un nombre sansprcdent de flambes hors saison de ce type qui stendentdans la communaut, comme lont montr les cas confirmschez des voyageurs ne prsentant pas de lien pidmiologiqueconnu avec des flambes localises. Des schmas analogues deflambes hors saison ont t observs lors de lmergence etde la transmission soutenue dautres souches du nouveauvirus grippal A chez lhomme.10

La rcente apparition du nouveau virus grippal A (H1N1) dansplusieurs pays de lhmisphre Sud au dbut de la saison grip-pale et la sensibilit prsume dune grande partie de cettepopulation ce nouveau virus suggrent que le nouveau virusgrippal A (H1N1) pourrait devenir le virus circulant dominantdans lhmisphre Sud au cours des prochains mois. Le Gouver-nement mexicain continue de coordonner la riposte nationale,de mobiliser des partenaires, daugmenter ses capacits de rac-tion et de mettre en oeuvre des mesures dattnuation afin deralentir la transmission du nouveau virus grippal A (H1N1). Desinvestigations sont en cours afin de surveiller la circulation du

virus et dvaluer limpact des moyens dattnuation, qui pour-raient aider orienter les stratgies de prvention et de lutteau Mexique et ailleurs dans le monde.

Au 1er juin 2009, 64 pays avaient signal au moins 1 cas confirmen laboratoire dinfection humaine par le nouveau virus grippalA (H1N1). Une grande partie de ces personnes ayant sans douteentam leur voyage alors quelles ne prsentaient pas de symp-tmes, la maladie tant cliniquement latente, le dpistage aumoment du dpart a ses limites pour matriser lexportation duvirus. Toutefois, une sensibilisation accrue des voyageurs sestrvle efficace pour favoriser une dclaration spontane parceux ci des syndromes dallure grippale aux autorits sanitairesaux points dentre.

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