RESUMO
BACKGROUND: The first pandemic influenza (H1N1) 2009 confirmed case acquired in the Madrid Region was diagnosed in May 20th. This was the index case of the first outbreak in a school in the Madrid Region (MR). The aim of this paper is to describe school outbreaks that took place during the spring in 2009, the control measures implemented and the beginning of the community transmission of this virus in the Region. METHODS: Descriptive observational study of school outbreaks due to pandemic (H1N1) 2009 virus reported between May 20th and June 27th, and total investigated cases in this period. It was used the definition of cluster of influenza cases adopted by National Authority (three or more cases). Clinical, epidemiological and microbiological data of cases were analyzed. RESULTS: There were identified 1.349 cases of pandemic (H1N1) 2009. They were associated with 77 school centres with three or more reported cases, 47,4% of total cases in this period (n = 2.844). 36 outbreaks were detected in Leganés (more than one third of all schools in the municipality), generating the highest cumulative incidence rates in the Basic Health Zone. There were differences by symptoms according to age. During this period, 949 samples were analyzed and 555 (58.5%) tested positive. CONCLUSIONS: The transmission of pandemic (H1N1) 2009 virus in the MR occurred steadily during the spring of 2009 due to schools outbreaks, meaning the onset of community transmission in Spain.