Prevalence of microbiologically-confirmed influenza in patients with influenza-like illness in primary care and clinical and epidemiological characteristics

Objectives. We evaluated the prevalence of microbiologi-cally-confirmed influenza infection among patients with influ-enza-like symptoms and compared the clinical and epidemio-logical characteristics of patients with and without influenza infection. Methods. Retrospective study of a cohort of patients with influenza-like symptoms from 2016 to 2018 who partic-ipated in a clinical trial in thirteen urban primary centres in Catalonia. Different epidemiological data were collected. Patients rated the different symptoms and signs on a Likert scale (absent, little problem, moderate problem and severe problem) and self-reported the measure of health status with the Euro-Qol visual analogue scale. A nasopharyngeal swab was taken for microbiological isolation of influenza and other microor-ganisms. Results. A total of 427 patients were included. Micro-biologically confirmed influenza was found in 240 patients (56.2%). The percentage of patients with moderate-to-severe cough, muscle aches, tiredness and dizziness was greater among patients with microbiologically confirmed influenza. The self-reported health status was significantly lower among patients with true flu infection (mean of 36.3 ± 18.2 vs 41.7 ± 17.8 in patients without influenza; p<0.001). Conclusion. Clinical findings are not particularly useful for confirming or excluding the diagnosis of influenza when intensity is not considered. However, the presence of moder-ate-to-severe cough, myalgias, tiredness and dizziness along with a poor health status is more common in patients with confirmed flu infection.