Severe Community-acquired pneumonia (SCAP) is a leading global infectious cause of intensive care unit (ICU) admission (approximately 20%-30%), and the primary reason of mortality and morbidity in immunocompromised patients. There is a global increase of patients with distinct immunocompromised conditions due to the advance of cancer treatment, increasing biologics, and immunosuppressants for autoimmune diseases and growing organ transplant recipients, and it has been estimated that patients with immunocompromised conditions account for approximately 35% of all intensive care unit (ICU) admissions. Immunocompromised patients with SCAP have more factors to complicate with sepsis, respiratory failure, acute respiratory distress syndrome, and the mortality rate can be up to 50%. With the aim to apply early accurate antimicrobial therapy to improve clinical prognosis of SCAP patients with immunocompromised conditions, timely identification of pathogen is particularly important. Conventional microbiological diagnostic methods such as standard microbiologic cultures, microscopy, polymerase chain reaction (PCR), respiratory virus multiplex PCR, as well as pathogen-specific antigens and antibody assays, are currently commonly used to detect pathogens, although they have various limitations. However, conventional antimicrobial therapy depends on the results of conventional diagnostic methods, which may delay timely accurate antimicrobial therapy at the initial stage, and the mortality of immunocompromised patients with SCAP may be increased. Metagenomic next-generation sequencing (mNGS), which can determine pathogens more quickly (usually within 24h) and accurately comparing with conventional diagnostic methods by analyzing cell-free nucleic acid fragments of pathogens using appropriate lower respiratory tract (LRT) specimen, is increasingly used in severe respiratory infectious disease, especially among immunocompromised patients. This study aims to determine whether mNGS (using LRT specimen) guided antimicrobial treatment improves clinical prognosis of SCAP patients with immunocompromised conditions when compared with conventional antimicrobial treatment.

Severe Community-acquired pneumonia (SCAP) is an emergence infection disease of lung parenchyma that acquired outside of a hospital setting. SCAP is a leading global infectious cause of intensive care unit (ICU) admission (approximately 20%-30%), and the primary reason of mortality and morbidity in immunocompromised patients. There is a global increase of patients with distinct immunocompromised conditions due to the advance of cancer treatment, increasing biologics, and immunosuppressants for autoimmune diseases and growing organ transplant recipients, and it has been estimated that patients with immunocompromised conditions account for approximately 35% of all intensive care unit (ICU) admissions. Immunocompromised patients, who always at risk of mixed and unusual pathogens infection, have more factors to complicate with sepsis, respiratory failure, acute respiratory distress syndrome, and the mortality rate can be up to 50%. Moreover, the outcomes in immunocompromised patients with SCAP not only related to disease severity but also related to delays initiation of receiving appropriate therapy. 2019American Thoracic Society (ATS)/Infectious Diseases Society of America (IDSA) community-acquired pneumonia (CAP) guideline recommends that administering appropriate antimicrobials as soon as possible is the most effective measure to improve clinical prognosis and reduce mortality rate for SCAP patients. Therefore, timely identification of pathogenic microorganisms is particularly crucial for antimicrobial treatment in immunocompromised patients with SCAP.

Conventional microbiology diagnostic methods, such as standard microbiologic cultures, microscopy, polymerase chain reaction (PCR), respiratory virus multiplex PCR, as well as pathogen-specific antigens and antibody assays, are associated with relevant limitations: (1) long culture cycle and low positive rate; (2) usually only one pathogen can be detected at a time; (3) inability to detect fastidious or difficult culture organisms; (4) pathogen antibody-based testing may be unreliable in immunocompromised patients who are unable to mount antibody responses. Conventional diagnostic methods make big challenge for pathogens diagnosis of SCAP among immunocompromised patients due to above limitations and the complicated causative microorganisms. However, conventional antimicrobial therapy based on the results of conventional microbiology diagnostic techniques, which may delay timely accurate antimicrobial therapy at the initial stage, and the mortality of immunocompromised patients with SCAP may be increased. Metagenomic next-generation sequencing (mNGS), which can quickly (usually within 24h) detect a wide array of bacteria, viruses and fungi in an unbiased manner at the same time by analyzing cell-free nucleic acid (DNA) fragments of pathogens using appropriate lower respiratory tract (LRT) specimen, is increasingly used in severe infectious disease, especially among immunocompromised patients. This study speculates that mNGS (using LRT specimen) can guide early and accurate antimicrobial treatment for immunocompromised patients with SCAP. This multi-center, opening, randomized, controlled trail will enroll SCAP patients with immunocompromised conditions to determine whether mNGS-guided antimicrobial treatment improve the clinical prognosis and increase the clinical cure rate. The purpose of this study is to characterize the effect of mNGS-guided antimicrobial treatment for SCAP versus conventional treatment among immunocompromised patients. It is postulated that mNGS-guided antimicrobial treatment for immunocompromised patients with SCAP will improve clinical outcomes among these patients.

Inclusion Criteria:

1. Meet the diagnostic criteria of sever community acquired pneumonia (SCAP).

   SCAP is defined as:

   With either one major criterion or at least three minor criteria of the IDSA/ATS CAP severity criteria.

2. Admission in ICU.

3. Time from SCAP diagnosis to ICU admission<24 h.

4. Patients with Immunocompromised conditions.

Immunocompromised conditions are defined as:

1. Use of long-term (>3 months) or high-dose (>0.5 mg/kg/d) steroids.
2. Use of other immunosuppressant drugs.
3. Solid organ transplantation.
4. Solid tumor requiring chemotherapy in the last 5 years.
5. Hematologic malignancy regardless of time since diagnosis and received treatments.
6. Primary immune deficiency.
7. HIV infection with a cluster of differentiation 4 (CD 4) T-lymphocyte count <200 cells/ml or percentage <14%.
8. Laboratory tests show absolute neutrophil count < 1,000 cells/µl on ICU admission.
9. Other immunosuppression status judged by the physicians.

Exclusion Criteria:

1. Age<18 years old.
2. Pregnant or lactating women.
3. Those who are expected to die within 72 h.
4. Receiving palliative therapy or supportive treatment only.

Study protocol and informed consent form will be shared with other researchers when start this trial.

Study protocol and ICF will be shared with other researchers when start this trial for five years.

Ever researchers can access our study protocol and ICF from the web of clinical trials.gov.