While adults presenting to primary care with acute cough that are diagnosed with pneumonia (based on chest radiograph) or a combined viral–bacterial infection (based on modern microbiological methodology) benefit from treatment with amoxicillin, we did not find any benefit on symptom duration, symptom severity or illness deterioration in patients where these diagnoses are based on clinical prediction rules, regardless of including biomarker information (CRP or PCT). The gene discussed is CRP; the disease is bacterial infectious disease.