Bad smell coming from sinuses. Could anaerobic bacteria be present in the nasal passages?

Sinusitis. Yes, both aerobic and anaerobic bacteria live within the sinus and nasal cavities. If your sinuses become obstructed and don't drain properly, an infection can develop (acute sinusitis) that is often foul-smelling due to the presence of anaerobic bacteria. This can also cause halitosis due to the communication between the oral cavity and the nasopharynx.