Arnold is a medical doctor, trained as an epidemiologist and medical consultant in public health. Until 2016 he headed the Public Health Training Section at the European Centre for Disease Prevention & Control (ECDC). During the 10 years at ECDC, he was leading the development of a new training programme in Public Health Microbiology ‘EUPHEM’, the design and development of an online community platform for public health information sharing ‘FemWiki’ and the design and development of the ECDC Virtual Academy ‘EVA’.
Prior to that he was chief scientific coordinator for the European Programme for Intervention Epidemiology Training ‘EPIET’. He has worked as senior consultant in outbreak response and project leader in surveillance at the National Institute for Public Health and the Environment ‘RIVM’ in the Netherlands. At the start of his public health career he was project leader of public health informatics projects in infectious disease surveillance and has worked for several years as a local communicable disease control consultant.