To know the possibility of spreading the infection and keeping others safe everyone wants to know the reason behind the sinus infection. Especially if you want to know if it’s viral or bacterial. But there is no way to do that just by the symptoms. Even the doctor can not tell that by the symptoms. They usually suggest the patients wait for a week, as the viral sinusitis starts to get well after 7-10 days.
There is a rumour that you can determine if it's a virus or bacteria by the colour of the mucus. But the doctors reject that idea completely. There are some other factors behind the yellow or green colour of the mucus including the white blood cells. Even the hydration level of the body can change the colour and thickness of the mucus.
The doctors usually know the infection type by its duration of it. But If you can not tolerate the symptoms for that time then the doctor will go through some tests. An endoscopy or a sample test can determine the reason for the infection. The doctor will also determine the bacteria to treat you properly.