Hi, We Have 3 Male Staff Employed (we Have 7

Hi, we have 3 male staff employed (we have 7 altogether) who have all been diagnosed with orchitis at the same time. They work very closely and job is very physical (boat building, welding, heavy lifting etc). From what little i have read about orchitis am unsure how it can be spread and what is likely to be causing it. Can you please give us some clue as why this has happened and how to prevent it affecting other staff or reoccuring. Is it contagious or a coincidence or related to the type of work they do?