Commonest cause for acute sinusitis is:
**Core Concept**
Acute sinusitis is an inflammatory condition of the paranasal sinuses, typically caused by a viral or bacterial infection. The commonest cause of acute sinusitis is a viral infection, which can lead to secondary bacterial infection.
**Why the Correct Answer is Right**
The most common viruses responsible for acute sinusitis are rhinoviruses, coronaviruses, and adenoviruses. These viruses cause upper respiratory tract infections, leading to inflammation and congestion of the nasal passages and sinuses. This congestion can trap bacteria and lead to secondary bacterial infections, such as Streptococcus pneumoniae or Haemophilus influenzae. The viral infection triggers an inflammatory response in the sinuses, which can cause symptoms such as nasal congestion, facial pain, and headaches.
**Why Each Wrong Option is Incorrect**
**Option A:** While allergic rhinitis can exacerbate sinusitis, it is not a direct cause of acute sinusitis.
**Option B:** Bacterial infections are a secondary cause of acute sinusitis, not the primary cause.
**Option C:** Fungal infections can cause chronic sinusitis, but are not the commonest cause of acute sinusitis.
**Clinical Pearl / High-Yield Fact**
The commonest cause of acute sinusitis is a viral infection, which can lead to secondary bacterial infection. It's essential to treat the underlying viral infection and manage symptoms to prevent complications.
**Correct Answer: A. Viral infection.**