Study subject will be recruited in the outpatient clinic of the Department of Pediatrics, or in the Pediatric Infectious Diseases Ward in the Turku University Hospital. Study physician/nurse or on-duty physician/nurse tells the guardian about the study and givens written information about the study. After the guardian has had adequate time the get familiar with the study and has had change to ask, his/her signature will be seeked to the informed consent form and the study will commence.