1 www.eurosurveillance.org Surveillance and outbreak reports 2009 pandemic influenza A(H1N1) outbreak in a complex of schools in Paris, France, June 2009 P Carrillo-Santisteve (p.carrillio@invs.sante.fr) 1,2 , S Renard-Dubois 3 , G Cheron 4 , M Csaszar-Goutchkoff 3 , M Lecuit 5 , O Lortholary 5 , P Y Bello 6 1. Infectious Diseases Department, Institut de Veille Sanitaire (InVS, French Institute for Public Health Surveillance), Saint Maurice, France 2. European Programme for Intervention Epidemiology Training (EPIET), European Centre for Disease Prevention and Control, Stockholm, Sweden 3. Local Health Authority of Paris (DASS), Paris, France 4. Université Paris-Descartes, Necker Hospital for Sick Children, Emergency Department, Paris, France 5. Université Paris-Descartes, Necker Hospital for Sick Children, Infectious and Tropical Diseases Department, Necker Pasteur Infectious Diseases Centre, Paris, France 6. Regional Epidemiology Unit of Ile de France (CIRE), Institut de Veille Sanitaire (InVS, French Institute for Public Health Surveillance), Saint Maurice, France Citation style for this article: Carrillo-Santisteve P, Renard-Dubois S, Cheron G, Csaszar-Goutchkoff M, Lecuit M, Lortholary O, Bello PY. 2009 pandemic influenza A(H1N1) outbreak in a complex of schools in Paris, France, June 2009. Euro Surveill. 2010;15(25):pii=19599. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19599 Article published on 24 June 2010 An outbreak of 2009 pandemic influenza A(H1N1), involving 81 cases with symptoms of influenza-like illness, was confirmed in June 2009 in a complex of schools in Paris, France. At that time, there was no community transmission in France. The index case, a 10-year-old girl, had travelled to the United Kingdom with her school class. Of the 81 symptomatic cases, 35 were confirmed and 46 were probable; 48 of the cases were female. Three were adults and 78 were children (median age of the children was 7.9 years, range: 6 months to 12 years). Control measures were implemented as soon as a new case was confirmed in a school, which included active case finding among the pupils in the same class as the index case, setting up a dedicated influenza outpatient clinic that families were recommended to consult if necessary, prophylac- tic treatment of contacts and school closure. A retro- spective study was conducted on all confirmed cases and all symptomatic cases who had consulted the dedicated outpatient clinic from 17 to 27 June 2009. Further work is needed to better define conditions under which the pandemic virus can be transmitted in schools and in households. Background In response to the appearance of the 2009 pandemic influenza A(H1N1) virus first detected in Mexico and the United States in April 2009 [1], France developed an active surveillance system for influenza-like illness [2-4]. Up to 8 July 2009, surveillance was aimed at pre- venting the introduction and community spread of the pandemic virus in France and was based on the identi- fication of all possible cases among recent travellers coming from affected areas [4]. On 19 June 2009, pandemic influenza was confirmed in a 10-year-old girl, who attended a primary school in Paris, France. At that time, there was no community transmission in France. The girl had travelled to the United Kingdom (UK) with her class (n=30) and three accompanying adults, returning to Paris on 12 June. She developed influenza-like symptoms on 17 June and was hospitalised the following day, for medical supervision and in order for samples to be taken, according to the recommended procedure at that time in the country [3]. Following the girl’s positive test for the pandemic influ- enza virus on 19 June, local health authorities were alerted and began to contact families of the other chil- dren in her class in order to assess their health and organise control measures, such as chemoprophylaxis. Between Friday 19 June and Sunday 21 June 2009, fami- lies of 27 of the 30 pupils were contacted by telephone. Eight children had developed influenza-like symp- toms (two of them had already recovered). The Necker Hospital for Sick Children, located close to the school, set up a dedicated influenza outpatient clinic [5]. Setting This pandemic influenza outbreak affected several schools. It began first in the primary school that the index case attended (School A, with 360 children aged between six and 11 years in 13 classes) and then spread to a nursery school (School B, with 253 children aged three to six years), to a day care school (School C, chil- dren aged three months to three years, total number of children unknown) and to another primary school in the neighbourhood (School D, 293 children aged six to 11 years). Siblings in the same family attended differ- ent schools, according to their age. The children shared common spaces: children in School B shared the main entrance and other facilities (such as the canteen) with School A, a gym in School D was open to the children of School A. A playground in