Infectious disease leads to deaths that accounted for more than 25% of all causes of human mortality. But the traditional microbiological diagnostic methods such as specimen culture are sometimes time-consuming, and have limited sensitivity. And some bacteria, anaerobes and viruses may be difficult to cultivate and isolation. Therefore, the accurate identification and rapid classification of pathogenic microorganisms is very important for the patient's precise diagnosis and timely treatment.

Small-scale studies on the diagnostic efficacy and prognosis of infection in the next generation have been shown to provide early diagnosis and targeted medication guidance for bloodstream infections and respiratory infections, but the larger-scale validation of next-generation sequencing Technology in the diagnosis and treatment of infectious diseases in the human body is relatively rare.

The purpose of this study is to provide rapid etiological diagnosis of patients by means of next-generation sequencing, to change the way of treatment of patients under the existing traditional pathogen detection by means of accurate description of pathogens and monitoring their dynamic changes, and to provide patients with more accurate treatment.

Inclusion Criteria:

• Patients are highly suspected of fever of unknown origin
• Patients are highly suspected of bloodstream infection
• Patients are highly suspected of respiratory infections
• Patients are highly suspected of central nervous system infection

Exclusion Criteria:

• Patients diagnosed as non-infectious diseases such as cancer and autoimmune diseases;

Patients that are highly suspected of infectious diseases, and they will be selected mainly from infectious diseases departments .