Incidence and prevalence of headache in influenza: A 2010–2021 surveillance-based study

Abstract

Background and purpose: Influenza is a common cause of acute respiratory infection, with headache being one of the symptoms included in the European Commission case definition. The prevalence of headache as a symptom of influenza remains unknown. We aimed to describe the incidence and prevalence of headache in patients with influenza. Methods: All consecutive patients who met the definition criteria of influenza-like illness during the influenza seasons 2010–2011 through 2021–2022 were included. The seasonal cumulative incidence of influenza per 1000 patients at risk and the prevalence of headache as an influenza symptom were calculated, including the 95% confidence intervals (CIs). Subgroup analyses were done based on patients' sex, age group, microbiological confirmation, vaccination status, and influenza type/subtype/lineage. Results: During the study period, 8171 patients were eligible. The incidence of headache in the context of influenza varied between 0.24 cases per 1000 patients (season 2020–2021) and 21.69 cases per 1000 patients (season 2017–2018). The prevalence of headache was 66.1% (95% CI = 65.1%–67.1%), varying between 49.6% (season 2021–2022) and 80.1% (season 2010–2011). The prevalence of headache was higher in women (67.9% vs. 65.7%, p = 0.03) and higher in patients between 15 and 65 years old. Headache was more prevalent in patients infected with B subtypes than A subtypes (68.7% vs. 56.9%, p < 0.001). There were no notable differences regarding vaccination status or microbiological confirmation of the infection. Conclusions: Headache is a common symptom in patients with influenza, with a prevalence higher than that observed in other viral infections.