Background: Chronic airway diseases (CAD), including chronic obstructive pulmonary disease (COPD), asthma and bronchiectasis, are highly prevalent and cause serious disease burden. Multimorbidity is recognized to influence treatment decision and prognosis of patients with stable CAD. The impact of multimorbidity on exacerbation CAD is under investigated.

Methods: The Chronic Airway Disease and Multimorbidity (CAM) cohort study is a prospective, multicenter, observational study aiming to recruit a minimum of 2000 patients hospitalized for exacerbation of COPD, asthma or bronchiectasis. Comprehensive data, including demographics, medical history, comorbidities, lung function, echocardiography, microbiological profiles, radiology, quality of life and treatment will be collected at baseline during the hospitalization. Follow-up data indicating the impact of both CAD and multimorbidity will be collected at 1-, 3-, 6-, 9- and 12-months after hospital discharge. Biospecimens, including blood and bronchoalveolar lavage fluid, will be collected and analyzed for biomarker detecting. Primary outcome are length of hospital stay and re-exacerbation during fellow-up. Secondary outcomes include comorbidity pattern and its impact on respiratory symptoms burden, quality of life, pulmonary function and chest imaging as well as cost and healthcare utilization.

Conclusions: The knowledge generated from CAM cohort study will fill crucial gaps in understanding how multimorbidity affects CAD and facilitate evidence-based clinical practice in the future.

The Chronic Airway Disease and Multimorbidity (CAM) Cohort is a nationwide, prospective, multicenter, longitudinal observational study aimed at understanding the epidemiology and impact of multimorbidity on patients hospitalized due to exacerbation of chronic airway diseases (CAD), including chronic obstructive pulmonary disease (COPD), asthma, and bronchiectasis. The study will enroll 2,000 patients across 9 medical centers in China, following their health trajectory for one year post-hospitalization.

Objective The primary objective is to assess how multimorbidity influences treatment outcomes, hospitalization length, and readmission rates in CAD patients. Secondary goals include analyzing comorbidity patterns, their effects on symptom burden, quality of life, pulmonary function, healthcare costs, and utilization.

Study Design Participants meeting inclusion criteria will be recruited through hospital advertisements and professional referrals. Upon providing informed consent, demographic, clinical, and laboratory data will be recorded during baseline hospitalization. The study employs standardized questionnaires and clinical tools such as mMRC, CAT, and SGRQ for quality-of-life assessments. Specimens, including blood, bronchoalveolar lavage fluid (BALF), and sputum, will be collected and stored for biomarker analysis. Imaging studies such as chest CT and echocardiography will evaluate disease severity and cardiac function.

Patients will be systematically followed at 1, 3, 6, 9, and 12 months post-discharge to record disease progression, treatment adherence, exacerbations, and outcomes.

Data Collection Demographics and Risk Factors: Age, gender, smoking history, family history, and occupational exposures.

Symptoms: Disease-specific tools such as CAT/mMRC(COPD), ACQ-7 (asthma) and BEST (bronchiectasis) will quantify symptom severity.

Quality of Life (QoL): SGRQ for COPD, QoL-Bronchiectasis for bronchiectasis, and mini-AQLQ for asthma patients.

Laboratory Data: Arterial blood gas, blood count, liver and renal function, inflammatory markers, and allergy panels.

Muti-morbidities: Systematic documentation of pulmonary and extrapulmonary comorbidities, including their diagnosis, treatment, and severity.

Outcome Measures: The primary outcomes are hospital length of stay and re-exacerbation rates. Secondary outcomes include changes in pulmonary function, QoL, mental health indices, imaging findings, and healthcare resource utilization.

Quality Control Data will be managed using an electronic data capture(EDC) system, with built-in validation to ensure accuracy. Periodic data audits and centralized training for research coordinators will enhance data integrity. Monitoring committees will address data discrepancies promptly.

Ethics and Dissemination The protocol complies with the Declaration of Helsinki and has received approval from ethics committees of all participating centers. The findings will inform clinical guidelines, emphasizing the integration of multi-morbidity management in CAD care.

This study bridges significant knowledge gaps in CAD management, particularly concerning multimorbidity in hospitalized patients, aiming to enhance evidence-based clinical practices.

Inclusion Criteria:

• Patients with chronic obstructive pulmonary disease ≥40 years of age; patients with asthma and bronchiectasis ≥18 years of age;
• The primary diagnosis on admission was "acute exacerbation of chronic obstructive pulmonary disease, uncontrolled asthma, or acute exacerbation of bronchiectasis".

Exclusion Criteria:

• Patients were unable to undergo spirometry during the stabilization period;
• Expected survival is less than 1 month;
• Refusal to sign an informed consent form;
• Chest imaging showed emerging patchy infiltrating shadows, lobar or segmental solid shadows, ground glass shadows, or interstitial changes with or without pleural effusion;
• Patients with cystic fibrosis or with interstitial lung disease or other lung diseases with tractional branchial dilatation.

The CAM cohort study focuses on hospitalized patients with chronic airway diseases (CAD), including chronic obstructive pulmonary disease (COPD), asthma, and bronchiectasis, during acute exacerbation episodes. Participants are recruited from 9 medical centers across China, representing diverse geographic and clinical settings.

The CAM cohort study has determined that individual participant data (IPD) will not be directly shared. Instead, supporting information and aggregated results will be made available in specific formats to ensure transparency while protecting participant privacy.