Infodemiology of cluster headache seasonality: A proof of concept by a Google Trends analysis.

Background: Cluster headache is commonly reported to follow an annual pattern with a peak in the spring and a second peak in autumn. Patients with headache frequently use search engines, such as Google, to look for terms related to their disease, creating trend data that can be analyzed with Google Trends. Indeed, Google Trends has been used for surveillance studies and can provide indirect estimates of the burden of diseases and symptoms. The present cross-sectional study investigated the seasonality of searches for "cluster headache" in the northern and southern hemispheres using 10 years of Google Trends data.

Methods: The term "cluster headache" or its translation in the 10 most spoken languages in the world was searched on Google Trends to obtain relative search volumes (from 0 to 100), in order to compare variations in searches across periods. Twenty-eight countries were selected according to the following criteria: (1) a relative search volume of >40 for the term for cluster headache; and (2) a population of at least 5 million inhabitants. For statistical purposes, countries were grouped in relation to hemisphere (northern or southern). Relative search volumes were extracted from January 2012 to January 2022 and analyzed according to two subgroups based on meteorological seasons (summer and winter vs. spring and autumn).

Results: A seasonal trend for in searches for cluster headache was found worldwide exhibiting higher relative search volumes in spring and autumn compared with summer and winter (17 [0, 39] vs. 13 [0, 37]; p = 0.016).

Conclusion: Higher search volumes for the term during the meteorological seasons of spring and autumn clearly reflect a circannual pattern of cluster headache occurrence, representing new evidence for its seasonality.