The changing landscape of Community-Acquired Pneumonia: from biomarkers to pneumococcal serotypes

Abstract

Community-acquired pneumonia (CAP) remains a major cause of illness and death worldwide, particularly among the elderly and individuals with underlying conditions. Streptococcus pneumoniae is the most common bacterial cause of CAP, but viruses such as influenza, RSV, and COVID-19 also play a significant role. Within the European PNEUMO study, we investigated how frequently pneumococcal pneumonia occurs, which S. pneumoniae serotypes are circulating, and what their disease burden is. During the COVID-19 pandemic, the number of bacterial pneumonias initially dropped sharply but later increased again. Serotypes 3, 11A, and 8 were found most frequently, some of which are not yet included in current vaccines. This highlights the need for broader vaccines and ongoing surveillance. A second theme of the thesis focuses on the use of biomarkers to improve pneumonia treatment. The biomarker procalcitonin (PCT) proved valuable in reducing unnecessary antibiotic use among COVID-19 patients without negatively affecting outcomes. However, in patients with influenza or RSV infection, the added value of PCT was less pronounced. Other biomarkers, such as suPAR, showed limited usefulness in predicting disease progression. Finally, we evaluated the applicability of diagnostic decision rules for excluding pulmonary embolism in COVID-19 patients, which showed that existing methods should be applied with caution. These findings contribute to a better understanding of pneumonia, more rational use of antibiotics, and improved strategies for future vaccination and treatment.