Sinus infections (also referred to as "acute sinusitis" or "acute rhinosinusitis") are quite common. Sinus infections can be thought of as either viral (also known as viral rhinosinusitis or the "common cold") or bacterial (also known as acute bacterial rhinosinusitis). When most individuals think of sinus infections, they are thinking of bacterial sinus infections but it is important to remember that sinus infections can be caused by viruses (which are not susceptible to antibiotics) as well. In both cases, the symptoms of a sinus infection, as defined by the American Academy of Otolaryngology - Head and Neck Surgery, are purulent (e.g. discolored) nasal drainage that is accompanied by nasal obstruction and/or facial pain-pressure-fullness. According to guidelines, one must have discolored, purulent nasal drainage to meet the criteria of a sinus infection.
Viral sinus infections/"common colds" are more common than bacterial sinus infections. It has been estimated that the average adult will experience 2 to 5 colds per year. Viral sinus infections may produce similar symptoms as bacterial sinus infections: discolored nasal drainage with nasal obstruction and/or facial pain/pressure. However, the key distinguishing factor with respect to symptoms is that with viral sinus infections, the symptoms peak at around day 3 - 5 and begin to improve thereafter (Figure 1). This why it is important to think about both how long sinusitis symptoms have been ongoing as well as their trajectory (getting worse, staying the same, or getting better) when it comes to deciding whether the sinusitis is viral or bacterial.
Bacterial sinus infections are a "complication" of approximately 2-5% of colds. In other words, the sinusitis starts as a viral infection but something then happens that causes the sinuses to be overtaken by bacteria, causing a bacterial infection. It is not clear what exactly this "something" is but one could imagine that the viral infection may create an environment that is more amenable to overgrowth of the bacteria that live in the sinuses, for example due to swelling of the lining of the sinuses which may even lead to the sinus drainage pathways swelling shut and leading to build up of mucus in the sinuses. Bacterial sinus infections may also occur spontaneously (without a noticeable cold before it) but these also occur in settings where the environment of the sinuses changes to promote bacterial overgrowth. For example, allergies (allergic rhinitis) may lead to swelling of the lining of the nasal cavity and also swelling of the drainage pathways of the sinuses, which may also lead to blockage of the sinuses and buildup of mucus that can create the perfect environment for bacterial overgrowth. Regardless of mechanism, it is estimated that each yea close to 20% of people experience a bacterial sinus infection.
Again, the symptoms of bacterial sinusitis are similar to those of a cold: discolored nasal drainage with nasal obstruction and/or facial pain/pressure. However, those symptoms are persistent and stable (not improving) or worsening after 5 days (Figure 2). The symptoms illustrated in Figure 1 and Figure 2 are from the European Position Paper on Rhinosinusitis and Nasal Polyps 2020, (which I refer to as "EPOS 2020") which is available online as open access.
There are a number of criteria that have been established for the formal diagnosis of the acute bacterial sinusitis. From the EPOS 2020 recommendations shown in Figure 2, bacterial sinusitis should be suspected when three of the following signs/symptoms are experienced:
Fever of above 100.5°F (38°C)
Double sickening (double worsening): when symptoms of a cold are getting better and then worsen as illustrated by the top blue dashed line in Figure 2.
(I am not mentioning the raised ESR/CRP because these require a blood test)
The 2015 American Academy of Otolaryngology - Head and Neck Surgery Clinical Practice Guidelines on Adult Sinusitis state that "A clinician should diagnose acute bacterial rhinosinusitis when (a) symptoms or signs of acute rhinosinusitis (purulent nasal drainage accompanied by nasal obstruction, facial pain-pressure-fullness, or both) persist without evidence of improvement for at least 10 days beyond the onset of upper respiratory symptoms, or (b) symptoms or signs of acute rhinosinusitis worsen within 10 days after an initial improvement (double worsening).
The Infectious Diseases Society of America also published guidelines on acute bacterial sinusitis in 2012, which is also available online as open access. These guidelines suggested that bacterial sinusitis be considered when:
There are persistent symptoms or signs compatible with acute rhinosinusitis, lasting for ≥10 days without any evidence of clinical improvement, or
Onset with severe symptoms or signs of high fever (≥39°C [102°F]) and purulent nasal discharge or facial pain lasting for at least 3–4 consecutive days at the beginning of illness, or
Onset with worsening symptoms or signs characterized by the new onset of fever, headache, or increase in nasal discharge following a typical viral upper respiratory infection (URI) that lasted 5–6 days and were initially improving (‘‘double- sickening’’)
The above is intended to show how we approach diagnosing bacterial sinus infections. As it is apparent, the exact diagnostic criteria for a bacterial sinus infection varies a bit depending who you ask and which source you go to. However, there are clearly some trends, which largely are based on the time course and trajectory of symptoms as I emphasized above. From a practical standpoint, if you have symptoms of sinusitis (nasal drainage accompanied by nasal obstruction and/or facial pain-pressure-fullness), think about how long you've had the symptoms and whether the symptoms are improving, staying the same or worsening and then refer back to Figure 1 and Figure 2. But here are some general guidelines that you can use:
Sinusitis symptoms are purulent (e.g. discolored) nasal drainage accompanied by nasal obstruction, facial pain-pressure-fullness, or both. If you are not having discolored, purulent drainage, then you probably don't have a bacterial sinus infection.
Inside the first 3-5 days it is very difficult to differentiate between a viral and bacterial sinusitis but if sinusitis symptoms are particularly severe, we may lean towards a bacterial sinus infection (and treat with antibiotics, although discussion of treatment for sinusitis is an entirely different discussion altogether!).
After 5 days, if sinusitis symptoms are worsening, that may indicate a bacterial sinus infection.
If sinusitis symptoms are generally stable and neither improving nor resolving, we generally wait until 10 days before deeming the infection to be likely bacterial in nature.
If you have questions, always feel free to reach out to your primary care doctor, local rhinologist or us.