Viral etiology in adult influenza-like illness/acute respiratory infection and predictivity of C-reactive protein

Influenza-like illness (ILI) and acute respiratory infection (ARI) are common presentations during winter and indiscriminate antibiotic use contributes significantly to the emerging post-antibiotic era. Otherwise healthy 152 patients, presenting to outpatient clinics with ILI/ARI, were included. Patients had history & physical, CRP, hemogram and nasopharyngeal swabs for rhinovirus A/B, influenza A/B, adenovirus A/B/C/D/E, coronavirus 229E/NL63 and OC43, parainfluenza virus 1/2/3, respiratory syncytial virusA/B, metapneumovirus and Mycoplasma pneumoniae, Chlamydia pneumoniae, Legionella pneumophila and Bordetella pertussis by PCR and for ABHS culture. Median (IR) age was 26.5 (16.5). Time to presentation was shorter in men (p = 0.027). Patients with rhinovirus had lower rates (20%) of myalgia (p = 0.043). Patients with influenza virus had higher rates (97%) of elevated CRP (p = 0.016). Logistic regression revealed that patients with ILI/ARI and CRP ≥ 5 mg/L were 60 times more likely to have influenza virus infection than other viral agents (OR = 60.0, 95% CI = 2.65 to 1,358.2, p = 0.010). Rhinovirus predominated in December (54%), March (36%), and April (33%). Influenza virus predominated in January (51%). Fever was most common with adenovirus (p = 0.198). All GABHS cultures were negative. Atypical organisms and Bordetella pertussis were negative in all but one patient. Influenza virus is the most likely pathogen in ILI/ARI when CRP ≥ 5 mg/L. This might be explained by tissue destruction. Myalgia is rare with rhinovirus probably due to absence of viremia. Negative bacteria by PCR and culture suggest unnecessary antibiotic use in ILI/ARI.