Previous researches have found the common colonization of Pneumocystis jirovecii (Pj) in the airways of people with chronic obstructive pulmonary disease (COPD). And this colonization may exacerbate airway inflammation and increase the frequency of acute exacerbation in people with COPD.

The goal of this clinical trial is to study if "decolonization treatment" (that is, removing these colonizing Pj) works to improve the prognosis of COPD colonized by Pj in adults. The main question it aims to answer is:

• Does the Trimethoprim-Sulfamethoxazole (TMP-SMX, an antibiotics) decolonization treatment reduce the frequency of acute exacerbation in participants with COPD colonized by Pj who have a high risk of acute exacerbation.

Researchers will compare TMP-SMX to a placebo (a look-alike substance that contains no drug) to see if TMP-SMX works to reduce the frequency of acute exacerbation of COPD.

Participants will:

• Take drug TMP-SMX or a placebo 2 tablet every day for 4 weeks.
• Visit the clinic after 2 weeks, 1 month, 3 months, 6 months and 12 months for survey questions, checkups and tests.
• Keep a diary of their symptoms and the number of times they experience acute exacerbations

Inclusion Criteria:

• Age 40 and above，male or female；
• COPD who meet the diagnostic criteria of the Global Initiative for Chronic Obstructive Lung Disease (GOLD) 2026 ( post-bronchodilator FEV1/forced vital capacity [FVC] ratio < 0.7 and post-bronchodilator FEV1% predicted ≥ 30%), and have documented history of high exacerbation risk (Group E, defined as exacerbation history of ≥ 1 moderate or severe acute exacerbation within 12 months prior to inclusion)；
• Background triple therapy (ICS + LABA + LAMA) for 3 months prior to randomization with a stable dose of medication for ≥1 month prior to inclusion; Double therapy (LABA + LAMA) allowed if ICS is contraindicated；
• PCR detection of Pneumocystis jirovecii in induced sputum is positive；
• Informed consent

Exclusion Criteria:

• Allergic to TMP, SMX or sulfonamide drugs；
• There are pneumonia or other infections that require long-term use of antibacterial drugs (such as tuberculosis, NTM, other fungi, etc.)；
• Having used antibiotics within the previous 4 weeks prior to screening；
• Experience of AECOPD events within the previous 4 weeks prior to screening;
• Having a definite immunodeficiency disorder or receiving immunosuppressive therapy (such as HIV, agranulocytosis, solid organ or hematopoietic stem cell transplantation, malignant tumors, using long-term high-dose hormones > 20mg/day prednisone equivalent for more than 4 weeks)；
• Severe liver and kidney dysfunction (ALT/AST > 3 times the upper limit of normal value, eGFR < 60 mL/min/1.73m²)；
• Pregnant, lactating women or those planning to become pregnant;
• Folic acid deficiency-induced microcytic anemia;
• Currently using coumarin, phenytoin, pioglitazone, repaglinide, rosiglitazone, glipizide or glibenclamide;
• Currently participating in other interventional clinical studies；