The goal of this randomized study to test the efficacy of different doses of IVIG (intravenous immunoglobulin) in the treatment of severe HFRS（hemorrhagic fever with renal syndrome）, and provide new clinical ideas for the treatment and prognosis of HFRS patients in the future.

This study will include all hospitalized patients with confirmed severe or critically ill HFRS from October 2021 to October 2023 from 9 centers.

Participants will receive IVIG 10g/d or IVIG 20g/d. All the participants will be given conventional liquid therapy and symptomatic and supportive treatment.

Participants will be collected demographic, epidemiological history, hospitalization information, clinical data, laboratory data, imaging results, treatment regimens, and outcomes data.

This is a multicenter, prospective, randomized controlled study which aims at evaluating the efficacy of different doses of IVIG (intravenous immunoglobulin) in the treatment of patients with severe HFRS(hemorrhagic fever with renal syndrome), and providing reference for the future application of IVIG in severe hemorrhagic fever with renal syndrome. This study will include approximately 100 patients with severe hemorrhagic fever with renal syndrome who are randomly assigned to either the IVIG 10g/d group or the IVIG 20g/d group in a 1:1 ratio. The participants in each group will receive treatments for 6 days. Both groups are given routine liquid therapy and symptomatic supportive treatment. The main endpoints include transformation rate, post-period rate, mortality rate, and duration of the disease. Secondary endpoints include the incidence of complications and length of hospital stay.

Inclusion Criteria:

The patients must meet all of the following criteria:

• Age ≥ 18 years, regardless of gender;

• Within 5 days of onset, hospitalized patients diagnosed with epidemic hemorrhagic fever (hemorrhagic fever with renal syndrome) must have at least one of the following laboratory test results:

  1. Positive for serum specific IgM(immunoglobulin M) antibodies;
  2. Or detect hantavirus RNA(ribonucleic acid) from patient specimens;
  3. Or the serum specific IgG(immunoglobulin G) antibody titer in the recovery phase is more than four times higher than that in the acute phase;
  4. Or hantavirus can be isolated from patient specimens.

• Meet any of the following criteria:

  1. Severe illness: meet any of the following criteria: (i) Platelet count 20-50×10^9/L; (ii) White blood cell count 15-30×10^9/L. 2. Critical illness: meet any of the following criteria: (i) Platelet count<20×10^9/L; (ii) White blood cell count>30×10^9/L.

• Volunteer to join this study and be able to sign or have a written informed consent form signed by a legal representative.

Exclusion Criteria:

Exclude patients who meet any of the following criteria:

• Patients with primary chronic kidney disease;
• Patients with severe diabetes, hypertension, heart, lung, gastrointestinal tract, liver, autoimmune disease or nervous system disease;
• Have a history of malignant tumors (including solid malignant tumors and hematological malignancies etc.);
• Recent use of potentially nephrotoxic drugs;
• Pregnant or potentially pregnant patients;
• Patients with a history of hypersensitivity to IVIG (intravenous immunoglobulin) ;
• Selective IgA(immunoglobulin A) deficiency patients with IgA antibodies;
• Known or suspected immunodeficiency (human immunodeficiency virus infection, primary immunodeficiency), use of immunosuppressive drugs (glucocorticoids);
• Alcoholics, drug abuse, and psychiatric patients
• Other conditions which researchers deem not suitable for inclusion.