Q fever in Spain: epidemiology and demographic characteristics of hospitalized patients (2016-2023)

Background: Q fever, caused by Coxiella burnetii, is a zoonosis with significant public health implications. Spain has the highest number of cases in the European Union/European Economic Area, but the clinical and hospitalization burdens remain poorly characterized. This study described the epidemiology, demographic and clinical characteristics, and geographical distribution of hospitalized Q fever patients in Spain from 2016 to 2023. Methods: We conducted a nationwide, retrospective study using the Spanish Minimum Basic Data Set for Hospitalization (MBDS-H). All hospital admissions with an ICD-10-CM code for Q fever (A78) between 2016 and 2023 were included. We analyzed demographic data, comorbidities, complications, length of stay, intensive care unit (ICU) admission, and mortality. We calculated hospitalization rates per 100,000 population. Temporal trends were assessed using Poisson regression. Results: We identified 3,358 hospitalizations for Q fever, representing an overall hospitalization rate of 0.89 per 100,000 population. The median patient age was 56 years (interquartile range [IQR] 42-70), and the cohort was predominantly male (72%). The median hospital length of stay was 9 days (IQR 6-15), and 8.3% required ICU admission. The overall mortality rate was 2.4%. The most common complication was pneumonia (32%). Significant upward trends were observed over the study period for patient age, hypertension, and acute heart failure (p<0.05). Geographical analysis revealed the highest hospitalization rates in the Canary Islands (2.33), La Rioja (2.16), and the Balearic Islands (1.93). Conclusion: This study highlights the hospitalization burden due to Q fever in Spain. The risk of hospitalization increases with age and the presence of predisposing conditions. The marked regional heterogeneity and high frequency of complications such as pneumonia underscore the need for enhanced surveillance and a strengthened One Health approach to control this zoonosis.