Acute cough in outpatients: what causes it, how long does it last, and how severe is it for different viruses and bacteria?

Objectives: To describe the symptoms, duration, severity, and microbiology of lower respiratory tract infection (LRTI) in outpatients.

Methods: Prospective cohort study of adults in US primary or urgent care with a chief complaint of cough and symptoms consistent with LRTI. Baseline data included demographics, signs, symptoms, and PCR for 46 viruses and bacteria. The severity of symptoms reported for ≤28 days follow-up via diary and text message. The Bronchitis severity score assessed severity at baseline; overall severity was defined as the area under the symptom severity curve.

Results: Of 718 patients with complete baseline data, 618 had valid PCR results, and 443 were followed until symptoms resolved. Of those with valid PCR, 100 (16.2%) had 1+ viruses detected, 211 (34.1%) had 1+ bacteria, and 168 (27.2%) had both. Symptoms more likely with viral or mixed infection included feverishness (36.7-38.4% vs. 18.5%), chills or sweats (36.0-38.1% vs. 17.9%), being generally unwell (78.2-81.3% vs. 64.9%), and myalgias (42.7-48.2% vs. 28.6%). Coloured sputum (42.9% vs. 23.2-29.5%) was more common with a bacterial infection. The mean duration of cough was 14.7 days with viruses (95% CI: 13.2-16.2), 17.3 with bacteria (95% CI: 15.9-18.6), 16.9 with mixed infection (95% CI: 15.2-18.6), and 18.4 with no detection (95% CI: 16.1-20.8). Overall severity of cough was lower for viral infections (20.9 points, 95% CI: 18.6-23.3) than for other groups (range 24.2-26.3). The most common potential bacterial pathogens were Haemophilus influenza (28.0%), Moraxella catarrhalis (16.2%), and Streptococcus pneumoniae (10.2%), whereas the most common viral pathogens were rhinovirus (17.3%), influenza (12.8%), SARS-CoV-2 (11.5%), and seasonal coronaviruses (8.1%).

Discussion: The mean duration of cough was 16.4 days. Consistent with European studies, the type of infection or potential pathogen was not an important predictor of the duration or severity of LRTI.