Etiology of the symptoms will not be searched for on individual basis in this study but a connection to RTI virus epidemiology is built by a sentinel surveillance, where occupational health clinics located in the premises of the participating companies send a standard number of weekly specimens collected from employees visiting the clinic. For possible GTI outbreaks a standard outbreak investigation principle will be followed, including 3-5 specimens. from typical patients will be collected. Common causative agents of the diseases will be searched for using real-time PCR techniques.