Infectious Agents that Cause Sinusitis

Bacterial Sinusitis
Bacteria are the most common infectious agents in sinusitis. The bacteria most commonly implicated in sinusitis are the following:

Streptococcus pneumoniae (also called pneumococcal pneumonia or pneumococci). This bacterium is found in between 20% and 43% of adults and children with sinusitis.

H. influenzae (a common bacteria associated with many upper respiratory infections). This bacterium colonizes nearly half of all children by age two, and it causes about 25% of sinusitis cases in this group. Studies have reported the presence of this bacterium in 22% to 35% of adult sinusitis patients.

Moraxella catarrhalis. Over three-quarters of all children harbor this bacterium and it causes about 25% of sinusitis cases.

Staphylococcus aureus (6% of adult cases).

Fungal Sinusitis
Fungi are uncommon causes of sinusitis, but the incidence of these infections is increasing. Funguses involved in sinusitis are the following:

The fungus Aspergillus is the most common cause of all forms of fungal sinusitis.

Others include Curvularia, Bipolaris, Exserohilum, and Mucormycosis.

There have been a few reports of fungal sinusitis caused by Metarrhizium anisopliae , which is used in biological insect control.

There are four categories of fungal sinusitis:

Acute or invasive fungal sinusitis. This infection is most likely to affect people with diabetes and compromised immune systems.

Chronic or indolent fungal sinusitis. This form is generally found outside the US, most commonly in the Sudan and northern India.

Fungus ball (mycetoma). This fungal sinusitis is noninvasive and occurs usually in one sinus, most often the maxillary sinus.

Allergic fungal sinusitis. This form typically occurs because of an allergy to the fungus Aspergillus (rather than being caused by the fungus itself). In such cases, a peanut butter-like fungal growth occurs in the sinus cavities that may cause nasal passage obstruction and the erosion of the bones.

Fungal infections can be very serious, and both chronic and acute fungal sinusitis require immediate treatment. Fungal ball is not invasive and is nearly always treatable.

Fungal infections should be suspected in people with sinusitis who also have diabetes, leukemia, AIDS, or other conditions that impair the immune system. Fungal infections can also occur in patients with healthy immune systems but they are far less common.

Viral Sinusitis. Viruses are directly implicated in only about 10% of sinusitis cases.

Infectious Agents in Chronic Sinusitis
The same organisms that cause acute sinusitis are often present in chronic sinusitis, but other agents are often detected in chronic cases that are not present in the original acute condition:

About 20% of chronic sinusitis cases are caused by Staphylococcus aureus (commonly called Staph infection). This bacteria may be present but is not usually the infecting agent in acute sinusitis.

Along with other bacteria, certain anaerobic bacteria, particularly the species Peptostreptococcus, Fusobacterium, and Prevotella, are found in 88% of cultures in chronic sinusitis cases. (Anaerobic bacteria exist without air.)

Fungi are the cause of about 6% to 8% of chronic sinusitis cases.It should also be noted that sometimes bacteria or other organisms do not appear to be directly involved with chronic sinusitis.