Sinusitis, commonly referred to as a sinus infection, involves the inflammation of the tissue lining the sinuses, which are air-filled cavities within the bones of the face. When this lining becomes inflamed, the narrow drainage passages become blocked, leading to a buildup of fluid, pressure, and symptoms like facial pain and congestion. If symptoms persist after a course of antibiotics, it indicates the underlying cause is not susceptible to the medication.
The Infection Isn’t Bacterial
The most frequent reason antibiotics fail is that the infection is not caused by bacteria, which are the microorganisms antibiotics are designed to target. Viruses, such as those responsible for the common cold, cause the majority of acute sinusitis cases. Viral sinusitis typically resolves on its own within seven to ten days, and antibiotics provide no benefit against the virus while promoting antibiotic resistance.
Inflammation mimicking a sinus infection can also be triggered by non-infectious causes, particularly allergies. Allergic rhinitis occurs when the immune system overreacts to airborne irritants like pollen or dust, causing the sinus lining to swell and obstruct mucus flow. This inflammatory response requires treatment with antihistamines or nasal steroids, not an antibacterial agent.
A less common cause of persistent symptoms is fungal sinusitis, which requires specific antifungal medications or surgical removal. This condition can range from a noninvasive allergic reaction to fungi, known as allergic fungal sinusitis, to a fungal ball (mycetoma) or a more serious invasive infection. Since standard antibiotics are ineffective against fungi, misdiagnosis results in treatment failure.
Bacterial Resistance and Drug Selection
Even when the infection is confirmed to be bacterial, the prescribed antibiotic may fail due to microbiology and drug action issues. The primary concern is antibiotic resistance, where bacteria have evolved mechanisms to survive drug exposure. Common sinusitis pathogens, such as Streptococcus pneumoniae and Haemophilus influenzae, have shown increasing resistance to older antibiotics.
Another challenge is selecting an antibiotic with the correct spectrum of activity that specifically targets the bacteria causing the infection. If the initial medication choice does not cover the specific strain present, the infection will continue. Furthermore, the closed-off structure of the sinus cavities challenges medication delivery, as some antibiotics struggle to penetrate the inflamed, mucus-filled spaces.
Compliance issues also promote treatment failure and resistance, particularly if a patient stops taking the medication when symptoms improve. Failing to complete the full course allows the hardiest bacteria to survive, multiply, and develop resistance. This incomplete eradication leads to a relapse where the subsequent infection is resistant to the previously effective drug.
Underlying Anatomical and Chronic Factors
Physical and biological factors within the nasal passages can predispose a person to chronic or recurrent sinusitis that resists standard treatment. Anatomical obstructions, such as a deviated nasal septum or nasal polyps, can physically block the tiny openings (ostia) that allow the sinuses to drain. Impaired drainage creates a stagnant environment where bacteria flourish, making it difficult for the immune system and antibiotics to clear the infection.
In chronic cases, defined as symptoms lasting 12 weeks or longer, bacteria often shift from free-floating organisms to forming a protective structure called a biofilm. A biofilm is a complex community of microorganisms encased in a matrix that adheres to the sinus lining. This layer acts as a shield, protecting the bacteria from the body’s immune cells and high concentrations of antibiotics, rendering the medication ineffective.
The patient’s overall health and immune function also influence the persistence of the infection. People with underlying immune deficiencies may struggle to mount an adequate defense against invading organisms, even with antibiotic support. The body is unable to effectively clear the remaining bacteria, leading to a prolonged or relapsing cycle of inflammation and infection.
Steps to Take When Symptoms Persist
If symptoms like congestion, facial pain, or discolored discharge continue after completing a full course of antibiotics, contact the healthcare provider for re-evaluation. Persistent symptoms are defined as those lasting more than ten days after the initial infection or those that improve but then worsen significantly (double-worsening). The next step involves a thorough diagnostic approach to identify the cause of the resistance.
This evaluation may include a nasal endoscopy, using a thin, lighted tube to inspect the sinus drainage pathways for polyps or anatomical issues. Imaging tests, such as a computed tomography (CT) scan, provide detailed images of the sinuses to identify blockages or structural abnormalities. The provider may also take a mucus sample (culture) from the sinus cavity to identify the specific pathogen and test its susceptibility to antibiotics.
Depending on the findings, the treatment plan shifts away from a simple antibiotic prescription. This may involve long-term use of topical treatments, such as prescription-strength nasal corticosteroid sprays or frequent saline nasal rinses, to manage inflammation and promote drainage. For structural issues or chronic disease unresponsive to medication, referral to an Ear, Nose, and Throat (ENT) specialist is necessary for advanced care, which may include procedures like balloon sinuplasty or functional endoscopic sinus surgery.