New contraction and latent pathogen are overarching concepts that encompass different disease causes, modes of onset, mechanisms of disease progression, and clinical classifications within warm febrile diseases. This section primarily elaborates on the types of disease onset.

New contraction and latent pathogen are the two most common and primary modes and types of disease onset in warm febrile diseases. When the pathogenic influence is contracted and the disease manifests immediately, it is referred to as new contraction; when the pathogenic influence is contracted but does not manifest immediately, with the pathogenic qi lying dormant within the body and the disease manifesting later, it is referred to as latent pathogen. The former is termed "new-contraction warm disease," also known as "external-contraction warm disease," as seen in Wenre Jingwei , which includes "Ye Tian-shi's Treatise on External Contraction Warm Heat" and "Chen Ping-bo's Treatise on External-Contraction Warm Disease." The latter is termed "latent-qi warm disease," hence latent pathogen is also referred to as latent qi. New contraction and latent pathogen are thus abbreviated terms for new-contraction warm disease and latent-qi warm disease, respectively. These two types exhibit significant differences in their modes of onset, mechanisms of disease transmission and change, primary sites of pathological changes, and even prognosis and outcomes, which will be discussed separately below.