Why are antibiotics ineffective against viral coughs but effective against bacterial ear infections?

Why Antibiotics Don't Help Most Coughs But Can Help Ear Infections

Most coughs are caused by viral infections that antibiotics cannot treat, while many ear infections are bacterial and respond to antibiotic therapy.

The Fundamental Difference: Viral vs. Bacterial Etiology

Acute Cough is Predominantly Viral

• Acute cough from common colds, acute bronchitis, and most respiratory infections is caused by viruses (respiratory syncytial virus, influenza, parainfluenza, rhinovirus, adenovirus, coronavirus), not bacteria 1.
• Antibiotics are completely ineffective against viral infections because they only work against bacteria 1.
• Antibiotics are rarely effective for acute cough and are not indicated for acute cough from the common cold, acute bronchitis, asthma, or mild exacerbations of chronic bronchitis 1.

Bacterial Ear Infections Respond to Antibiotics

• Many middle ear infections (acute otitis media) are caused by bacteria such as Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis.
• When bacteria are the causative organism, antibiotics like amoxicillin directly kill or inhibit these pathogens, leading to resolution of infection 2.

Evidence Against Antibiotics for Cough

Guideline Recommendations

• The American College of Chest Physicians strongly recommends that antibiotics should not be routinely prescribed for acute bronchitis in healthy adults 1.
• Multiple guidelines emphasize that routine treatment with antibiotics for acute cough is not justified and should not be offered 1.
• The American Academy of Otolaryngology states that clinicians should not routinely prescribe antibiotics to treat dysphonia (hoarseness with cough) based on systematic reviews showing ineffectiveness and preponderance of harm over benefit 1.

Clinical Evidence

• A 2024 study of 718 patients with acute lower respiratory tract infection found that antibiotics had no measurable impact on the severity or duration of cough, regardless of whether patients had viral, bacterial, or mixed infections 3.
• Antibiotics provide only minimal benefit in acute bronchitis, reducing cough duration by approximately half a day while causing adverse effects including allergic reactions, nausea, vomiting, and Clostridium difficile infection 4.
• Even in patients predicted to have pneumonia or combined viral-bacterial infection, amoxicillin showed no significant benefit for symptom duration or severity 5.

When Antibiotics ARE Appropriate for Cough

Specific Bacterial Conditions

Antibiotics are likely to be effective for:

• Pneumonia confirmed by clinical findings (tachypnea, tachycardia, dyspnea, focal consolidation) or chest radiograph 1.
• Bacterial sinusitis causing upper airway cough syndrome 1.
• Pertussis (whooping cough) if given early in the illness—macrolide antibiotics like azithromycin are first-line treatment 1, 6.
• Severe chronic bronchitis exacerbations in current or previous smokers with severe airflow obstruction 1.

Clinical Clues for Bacterial Infection

• Biphasic illness pattern: If cough worsens after initial improvement or doesn't steadily improve after the first week, consider bacterial superinfection 1.
• Pertussis indicators: Paroxysmal coughing, post-tussive vomiting, whooping cough, known pertussis exposure, or cough persisting beyond 2 weeks 6, 4.
• Pneumonia indicators: Heart rate >100 bpm, respiratory rate >24 breaths/min, temperature >38°C, focal consolidation on exam 1.

The Harm of Inappropriate Antibiotic Use

Individual Patient Risks

• Direct adverse effects: allergic reactions, rash, abdominal pain, diarrhea, vomiting 1.
• Risk of Clostridium difficile infection 4.
• Increased risk of laryngeal candidiasis 1.
• Unnecessary costs—medications account for one-fifth to one-third of total direct costs in managing respiratory disorders 1.

Societal Impact

• Antibiotic overprescription contributes to bacterial antibiotic resistance, including methicillin-resistant Staphylococcus aureus 1.
• Regions with higher antibiotic resistance have 33% higher treatment costs for infectious diseases 1.
• Resistance increases complexity of treating routine infections and negatively affects patient outcomes 1.

Appropriate Management of Viral Cough

Patient Education is Critical

• Emphasize that acute cough typically lasts 2-3 weeks and gradually improves 1, 4.
• Explain that antibiotics do not treat viral infections and will not shorten illness duration 2, 4.
• Office time must be set aside to explain why antibiotics are not needed, as many patients expect them based on previous experiences 1.

Symptomatic Treatment Options

• First-generation antihistamine/decongestant combinations or naproxen are strongly recommended unless contraindicated 1.
• Newer-generation nonsedating antihistamines should be considered 1.
• For post-infectious cough, consider inhaled ipratropium or a trial of inhaled corticosteroids if quality of life is significantly affected 1.

Common Pitfall to Avoid

Do not prescribe antibiotics based solely on purulent sputum production—the onset of purulent sputum during acute bronchitis in healthy adults is not associated with bacterial superinfection 1.