We were having a work discussion on sinus infections. Are they contagious?


This is a common question, and a good one.

Literally, the word “sinusitis” means inflammation of the paranasal sinus, due to four generally accepted reasons:

  1. A viral upper respiratory infection (a.k.a. a “cold”)
  2. Environmental allergies (allergic rhinitis)
  3. Exposure to airborne pollution
  4. Bacterial infection


Of these four causes, the first (URI) is contagious (the others are not), and the last (sinusitis caused by bacteria) is the only one that improves with antibiotic treatment. (Denial that air pollution causes adverse health effects, despite decades of scientific evidence — and common sense — to the contrary, appears to be very contagious among those who have political, ideological, and economic interests which conflict with public health, but that’s another blog post for another day.)

Although the first three causes of inflammation are not caused by bacteria, anything that promotes swelling of the mucus membranes of the nose and sinuses can effectively block the natural draining anatomy of the sinuses (the ostiomeatal complex). Since bacteria like to grow in places that are warm and wet, secondary bacterial infections can result if the initial inflammation (from a preceding cold, ongoing allergy symptoms, or chronic exposure to pollution) persists.

There are three bacteria which are responsible for the bulk of acute bacterial sinusitis: Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. All three bacteria naturally colonize the nasal passages of all humans (they are not contagious) and generally cause no harm unless our immune system drops its guard. Colds, allergic rhinitis, and air pollution do a good job in overcoming the body’s natural defenses, allowing these otherwise harmless bacteria to wreak havoc and cause a spectrum of bacterial infections that vary in severity, from mild-to- very severe. Knowing which bacteria is causing which sinusitis can be a challenge since there is no easy and practical way to know for sure. Treating them with the proper antibiotics can be equally tricky.

Most common viral upper respiratory infections (colds) last for 5-7 days. Research supports the consensus that cold symptoms must last at least 10 days for the diagnosis of acute bacterial sinusitis to be considered. At this point, other symptoms are usually present: thick, yellow-green (purulent) nasal drainage and a daytime cough that may be worse at night. (It should be noted that the nasal discharge doesn’t have to be purulent — or even present; a cough, usually loose, that lasts for more than 10 days might be the only symptom, even after the initial nasal congestion has resolved.) Fever is often absent or low-grade in children with acute bacterial sinusitis. Headaches and facial pain are not common symptoms. Parents will sometimes report “bad breath” during a sinus infection, but in children, that is a non-specific complaint.

Still, it’s sometimes not easy for a pediatrician to be certain that that runny nose, fever, and cough is just a viral cold (the dreaded “justavirus”) or a bacterial sinusitis. Sometimes children will still be congested on day 10. If the symptoms are improving, however, they probably need a little more time (an additional week or so) to be completely better. The nasal drip for uncomplicated colds usually starts clear, then turns cloudy and even yellow, before turning clear again and going away. Drainage that turns yellow-green and stays that way at the 10-day mark probably represents a bacterial sinusitis. Also, fevers usually occur at the beginning of viral upper respiratory infections. A fever which lasts longer than 3-4 days from the start of a cold, or one that begins several days or a week (or more) after the start of a cold, sometimes means a secondary bacterial infection has settled in the sinuses, or the ears, or the lungs (or all three). These are times when we will recommend a visit to our office.

The diagnosis of acute bacterial sinusitis is not always a simple one. Whether or not to prescribe an antibiotic — and which one to use — can be complicated. “If you’re not sure,” you might ask, “then what harm might come from prescribing one?”

The answer to that question is “plenty.” We’ll have more about that tomorrow on The PediaBlog.