**9.2. Gene expression**

Gene expression profiles of peripheral blood leukocytes can differentiate viral from bacterial infections with 95% accuracy. They can also identify unique profiles in patients with bacterial and viral respiratory tract infections. Application of gene expression profile analysis in children with CAP can significantly enhance the ability to classify patients according to the class of pathogen causing the infection and disease severity. Molecular distance to health (MDTH) is a novel metric that in a single score can provide a global assessment of the perturbation of the patient immune profile compared to healthy controls. It has been shown to accurately classify the severity of the disease in for example cases of bacterial sepsis, staphylococcal infections, as well as in children with respiratory viral infections [82].
