July 22, 2011
Dear Mayo Clinic:
Can doctors tell if a sinus infection is bacterial or fungal? I've heard that some chronic infections can be related to a fungus.
Using lab tests, doctors can differentiate between a sinus infection that's caused by bacteria and one caused by fungus. Most acute sinus infections aren't caused by fungus. Sometimes, they're due to bacteria. More often, though, they result from viruses, like those that cause colds or other respiratory tract infections. Fungal sinus infections are rare and are mainly seen in people whose immune systems aren't working normally, such as those who have had chemotherapy or an organ transplant.
The second part of your question about chronic infections being associated with a fungus is actually related to another topic: chronic sinusitis. Some people who have sinus symptoms, such as a stuffy nose, nasal drainage and a decreased sense of smell, assume they have a sinus infection. If the symptoms appear after a cold, that may be true. An infection caused by bacteria, can often be effectively treated with antibiotics. Viral infections typically go away without treatment. And once an infection is gone, symptoms usually fade. But if nose and sinus symptoms persist longer than 12 weeks, the condition is classified as chronic sinusitis. Probably what you've heard about is that some research has linked chronic sinusitis to fungus.
Doctors used to believe that chronic sinusitis was a bacterial sinus infection that couldn't be effectively treated. But then it was found that steroids — medications used to reduce inflammation — could temporarily clear sinusitis even in patients who didn't take antibiotics. Because steroids won't usually clear an infection, the logical conclusion was that, more likely, the problem was something causing inflammation in the sinuses.
The key question is: What drives the inflammation of chronic sinusitis? Various causes have been proposed, including allergies, irritants, an immune reaction to fungus, a reaction of the immune system against a toxin made by bacteria, and persistent inflammation of bone.
What you've heard about fungus being related to sinusitis is likely due to research done at Mayo Clinic that started more than 10 years ago. That research pointed to the possibility that, in some people, a fungus in the air may lead to chronic sinusitis. These people appear to have a change in their immune systems — possibly triggered by a previous cold or other respiratory infection — that causes part of their defense system, called eosinophils, to attack the fungus.
Eosinophils are one of the major types of disease-fighting white blood cells. Eosinophils usually attack parasites and aren't usually active when your body is fighting a viral, bacterial or fungal infection. But for reasons that are still under investigation, in some situations the body's immune system is altered slightly, and a certain protein in the fungus appears to the immune system to be just like a parasite. So, eosinophils attack it. Actually, the 'problem' is just a mild-mannered fungus that most people have no reaction to when they breathe it in. But the resulting immune response in the people who are affected can cause the inflammation and symptoms of chronic sinusitis.
If you have chronic sinusitis, no matter what the underlying cause, treatment is available to relieve symptoms. For example, saline nasal spray may be used to rinse nasal passages and decrease the presence of triggers. Nasal corticosteroid sprays can be helpful in reducing inflammation. When sinusitis is severe, oral or injected corticosteroids may be necessary to decrease symptoms. It is also possible to get a bacterial infection on top of the inflammation, and that can be treated with antibiotics.
If you have ongoing sinus symptoms and suspect chronic sinusitis, see your doctor for an assessment of your condition and a treatment plan that fits your situation.
— John Pallanch, M.D., Otorhinolaryngology, Mayo Clinic, Rochester, Minn.