Sinus and upper respiratory tract infections, including kennel cough (tracheobronchitis) are very contagious, and can be easily transmitted by aerosol in
any environment where dogs
can congregate in
groups, such as kennels, puppy day camps, dog parks, in multiple dog walking situations, and during hospitalization, etc. Dogs even have their own "common cold", which is viral. But a secondary bacterial infection can also be implicated.