The study is designed to investigate difference in percentage of presentation of atelectasis, bronchiectasis, bronchiolitis obliterans, or consolidation in 6 months after discharge in those treated with a low dose regimen of methylprednisolone initiated with 2 or 4 mg/kg/d for 3 days followed by tapering, combined with sequential treatment with azithromycin versus a high dose regimen of methylprednisolone initiated with 10 mg/kg/d for 3 days followed by tapering, combined with sequential treatment with azithromycin.

Mycoplasma pneumonia pneumonia (MPP) accounts for approximately 10-30% of childhood community-acquired pneumonia (CAP) in China. Macrolide is the first choice for MPP. However, progression to severe pneumonia might occur despite antibiotics therapy. And some patients have sequelae of bronchiolitis obliterans, bronchiectasis and atelectasis, et al. Based on inflammatory and immunological mechanism, there is some clinical evidence that adjuvant of corticosteroid reduced morbidity and improved the outcome in the children with severe MPP. However, the dosage of corticosteroid varied greatly in studies. Therefore, a large prospective study is needed to define the benefits of high-dose corticosteroid therapy in MPP.

Patients will be randomized into two groups: the low dose group and the high dose group. The low dose group will receive methylprednisolone 2 or 4 mg/kg/d for 3 days followed by tapering in 9 days, combined with sequential treatment with azithromycin. The high dose group will receive methylprednisolone 10 mg/kg/d for 3 days followed by tapering in 9 days, combined with sequential treatment with azithromycin. After discharge, patients of both groups will be followed up at 1, 3, and 6 months.

The number of pulmonary lesions, including atelectasis, bronchiectasis, bronchiolitis obliterans, or consolidations, in 6 months after discharge will be compared in two groups. The number of adverse events, such as hyperglycemia, hypertension, increased intraocular pressure, will be compared between the two groups.

The trial will be completed in 36 months, with 424 subjects recruited from 5 hospitals in partnership with clinical research collaboration of National Clinical Research Center for Respiratory Diseases.

Inclusion Criteria:

Severe pneumonia diagnosis criteria were based on the "Zhu Futang Practical Pediatrics" (the 7th Edition) and "the guideline of management of community-acquired pneumonia in children in China"(Chinese Journal of Pediatrics, 2013, 51:745-752, 856-862). Severe pneumonia is defined as pneumonia with one of the following:

1. Less than 18 years old

2. Severe pneumonia that is defined as pneumonia with one of the followings:

   • poor general condition
   • increased respiratory rate( infant>70/min，older children>50/min)
   • dyspnea
   • cyanosis
   • multilobe involvement or ≥ 2/3 lung involvement
   • extrapulmonary complication
   • pleural effusion
   • Transcutaneous oxygen saturation in room air ≤92%

3. Serum M. pneumoniae antibody≥ 1:320, or serum M. pneumoniae antibody≥ 1:160 with positive PCR of M. pneumoniae or seroconversion (increased antibody titers ≥4 folds) Subject/Guardian is informed and consent.

Exclusion Criteria:

Subject will be excluded if she or he has one of the following:

• evidence of bacterial pneumonia;
• evidence of viral pneumonia;
• evidence of fugal pneumonia;
• evidence of pulmonary tuberculosis;
• respiratory failure requiring mechanical ventilation;
• hemophagocytic syndrome;
• liver failure or renal insufficiency;
• congenital heart disease;
• heart failure;
• kidney disease;
• connective tissue disease;
• immunodeficiency;
• tumor;
• a history of hypertension or diabetes mellitus;
• recurrent respiratory tract infection;
• congenital bronchopulmonary dysplasia;
• increased intraocular pressure;
• history of use of glucocorticoids ≥1 week in previous 3 months;
• having contraindications to glucocorticoids or azithromycin;
• using of immunosuppressant before randomization;
• undergoing trial for other medications or instruments.