The procedure for contact tracing is complex, see Figure 1 . Requests for contact tracing to the CIb for Dutch index patients originate from any Dutch MHS which identifies a patient who traveled by plane while being contagious for an infectious disease which requires contact tracing. Other nation's health authorities will make a request to the CIb in case they diagnosed a patient which arrived at Schiphol airport for transit while being infectious. Requests for CT in the last group are submitted to the National Focal Point (NFP) or through the Early Warning and Response system of the EU (EWRS). The CIb verifies laboratory confirmation, and the indication for contact tracing regarding flight duration. The MHS of the airport where the specific flight landed coordinates contact tracing for flight passengers. In case of Schiphol, MHS Kennemerland approaches the involved airline company requesting the passenger list. The airline provides passenger lists with at least passenger names, seat numbers and booking or contact details. MHS Kennemerland then completes contact details through booking offices or using other search methods. Close contacts living in the Netherlands are traced by the respective Dutch MHS's. For tracing foreign contacts, the CIb sends a notification with contact details to the NFP of the country of final destination, or through the EWRS system for EU countries.