Can a sinusitis still be there after treatment with antibiotics?

Yes, but... Several things contribute to chronic sinus problems.Most issues are not truly infections, but usually more congestion, especially if present after treatment. Avoid smoking and smoke exposure, explore allergies, consider nasal saline irrigation, and avoiding dairy products for 2 weeks (most adults have some version of milk allergy)recurrent issues can be from lacking some immunologic factors.
Yes. "sinusitis" refers to inflammation of the sinuses, which is commonly due to allergies, reflux, and other conditions. "acute sinusitis" refers to either a viral or bacterial infection; if it is bacterial, treatment with antibiotics should eliminate the infection. But if the infection was caused by chronic inflammation from allergies, this inflammation will still be there.

Related Questions

Can a sinusitis be uncured after 10 days of treatment with antibiotics?

Often. In many cases, if it is bacterial, and the correct antibiotic is used. Sometimes a culture needs to be obtained for hard to treat bacterial infections. Viral infections won't respond to antibiotics as viruses are not killed by antibiotics! Read more...