What are the key clinical features to differentiate between a viral and bacterial cause of acute cough in adults?

Differentiating between a viral and bacterial cause of acute cough in adults primarily relies on assessing the severity of illness and the presence of patient risk factors, rather than specific cough characteristics ¹,².

• Features suggesting a more serious (potentially bacterial) cause or need for antibiotics:
  • Systemically very unwell: This is a key indicator for considering an immediate antibiotic prescription ¹,². Signs of serious illness include a respiratory rate of more than 30 breaths per minute, tachycardia greater than 130 beats per minute, systolic blood pressure less than 90 mmHg, oxygen saturation less than 92% (or central cyanosis), peak expiratory flow rate less than 33% of predicted, altered level of consciousness, or use of accessory muscles of respiration ¹. For suspected pneumonia, additional signs of severity include a temperature higher than 38°C or lower than 35°C, a heart rate over 100 beats per minute, or inability to eat without assistance ⁵.
  • Higher risk of complications: Patients in this category may be considered for an immediate or backup antibiotic prescription ¹,². This includes individuals with pre-existing comorbid conditions such as heart, lung, kidney, liver, or neuromuscular disease, immunosuppression, or cystic fibrosis ². Also, adults older than 65 years with two or more of the following: hospital admission in the previous year, Type 1 or Type 2 diabetes mellitus, history of congestive heart failure, or current use of oral corticosteroids; or those older than 80 years with one or more of these factors ².
  • Worsening or non-improving symptoms: If symptoms worsen rapidly or significantly, or do not improve after 3 to 4 weeks, medical advice should be sought, as this could indicate a bacterial infection or other serious condition ¹,².
  • Focal chest signs: These may be present in a clinical diagnosis of community-acquired pneumonia ⁵.
• Features suggesting a less serious (likely viral) cause:
  • Typical duration: Acute cough, often associated with acute bronchitis, is usually a self-limiting illness and typically persists for up to 3 or 4 weeks ¹,².
  • Absence of severe signs or risk factors: If the person is not systemically very unwell and is not at higher risk of complications, antibiotics are generally not offered, as the cough is likely viral and self-limiting ¹,².