<qa>  What is the most important and effective measure to prevent the transmission of infections?School absenteeism due to respiratory infections is one of the greatest problems in schools. Its high incidence and easy transmission among pupils have a great impact requiring a vast number of medical visits, hospitalisations, use of antibiotic and antipyretic treatments, symptomatic medication, etc. besides being a cause for school absenteeism and time off work for parents. Hand- washing is the most important and effective measure to prevent the transmission of infections. The investigators evaluated the effectiveness of a hand-washing programme using hand sanitizer in the prevention of school absenteeism due to upper respiratory infections. 