To distinguish between viral and bacterial sinusitis, two symptoms shall be taken into account: purulent nasal discharge for three (3) days accompanied by high fever, and no improvement in the infection for at least ten (10) days. Since many symptoms are common in bacterial sinusitis and common cold, the symptoms’ duration is used for differential diagnosis. Based on the duration, bacterial sinusitis is divided into five different categories: acute, recurrent acute, subacute, chronic and acute exacerbation of chronic.

The bacteria found in the nasopharynx cause acute bacterial sinusitis. The most common bacteria include Moraxella catarrhalis, H. influenzae and Streptococcus penumoniae. The infection lasts from ten (10) days to four (4) weeks in case of acute bacterial sinusitis. The patient may have severe and non-severe symptoms. Nasal congestion, headache and facial pain could be severe and non-severe. Other severe symptoms include periorbital edema and colored, opaque and thick rhinorrhea. 

The non-severe symptoms consist of rhinorrhea of any type, cough and irritability. High fever indicates severe condition, whereas absence of fever or low fever represents non-severe case of sinusitis.

In case of recurrent acute sinusitis, four or more incidences of the acute infection may occur every year. Each incidence may linger for a week to ten days. Between the incidences of acute bacterial sinusitis, there are absolutely no symptoms of the disease. The patient quickly responds to an antibiotic treatment. The physician may suggest sinonasal cultures to select an appropriate antibiotic. Endoscopic sinus surgery may also be required to treat the recurrent symptoms. The pathogens causing an acute condition may trigger recurrent acute bacterial sinusitis.

Subacute sinusitis is a transient stage between acute and chronic bacterial infections. The infection may exist for 4-12 weeks. Moraxella catarrhalis, H. influenzae and S. penumoniae commonly cause acute and subacute bacterial sinusitis. Cough due to subacute sinusitis is treated with antibiotics and antihistamine-decongestants.

The infection lasting more than twelve (12) weeks is defined as chronic bacterial sinusitis. In case of subacute and chronic conditions, fever is uncommon, but sore throat and nasal congestion are common. Chronic bacterial sinusitis rarely occurs in children.

All bacteria causing acute symptoms may lead to chronic condition. Respiratory anaerobes, Streptococcus aureus, Pseudomonas aeruginosa and H. influenzae play a major role. However, role of other bacterial pathogens causing acute condition decreases.

This condition refers to sudden deterioration of the chronic infection. A new set of symptoms may also develop. Common bacteria responsible for acute community acquired sinusitis may cause acute exacerbation of chronic disorder.