Abstract

1.Overview of the surveillance

The surveillance of chronic obstructive pulmonary disease among Chinese residents（COPD surveillance）is the survey organized and implemented by the National Center for Chronic and Noncommunicable Diseases Control and Prevention（NCNCD），under the leadership of the Disease Prevention and Control Bureau of the National Health Commission.The work is coordinated by the Chinese Center for Disease Control and Prevention（China CDC），and technologically assisted by the clinical experts.The aim is to establish a COPD surveillance system suitable for national conditions，to learn the prevalence and trends of COPD and related factors among residents aged 40 years or older in China，and to provide a scientific basis for the development of policies on COPD prevention and control.It is also aimed to establish a team to monitor and control COPD with high quality and technical ability.

In 2014，for the first time，COPD surveillance was included in the National Major Public Health Project - chronic disease and nutrition surveillance project，as an important part of chronic disease prevention and control projects in the special projects of central subsidy for local public health.According to the requirements of “The Notice of the Ministry of Finance and the National Health and Family Planning Commission on the Issuance of 2014 Public Health Service Subsidy Fund”（Financial community ［2014］ No.37）and “The Notice of the Chinese Center for Disease Control and Prevention on the Relevant Requirements for the Implementation of Chronic Diseases and Nutrition Surveillance in Chinese Residents”（China CDC Chronic Disease Community ［2014］No.397），the NCNCD Center of China CDC first organized and implemented the COPD surveillance among Chinese residents at 125 counties/districts in 31 provinces from 2014 to 2015.The COPD surveillance is conducted every five years based on the National Disease Surveillance Points（DSPs）.

A multi-stage stratified cluster random sampling method was used to design the sampling frame in the COPD surveillance among Chinese residents.Considering the regional and urbanrural representation and geographical distribution balance，the national DSPs were divided into three stratifications according to the region（East，Middle，and Western），and each stratification was divided into two sub-stratifications in accordance with the level of urbanization（high and low）.The counties/districts of COPD surveillance were randomly selected from the national DSPs in each substratification.The number of counties/districts was allocated in proportion to the population size of 31 provinces，and at least two counties/districts in each province.At each selected DSP，three subdistricts in urban areas or townships in rural areas were randomly sampled.Then two neighborhood communities or administrative villages were randomly chosen within each sub-district/township.One group of villagers with at least 150 households with residents aged 40 years or order was randomly selected within each neighborhood community or administrative village.At last，100 households within each group of villagers were randomly chosen.In the final stage，one family member who was at least 40 years old was selected randomly from each household.The survey was planned to investigate 75，000 individuals and 75，107 participants completed the interview.The results of COPD surveillance were nationally representative.

The COPD surveillance included interview，anthropometric measurement and pulmonary function test which were conducted in local health stations or community clinics in the participants’residential area.The interview included the family questionnaire and the personal questionnaire.The family questionnaire mainly collected the basic information of the family，the family member registration and the family contact process.The personal questionnaire collected information on demographic characteristics，awareness and knowledge on the disease，respiratory symptoms，disease management，risk factors such as smoking，indoor polluting fuel exposure，exposure to dust or chemicals in the workplace，and pulmonary function test contraindications.Anthropometric measurement included the measurements of height，weight，waist circumference，blood pressure，and heart rate.All subjects underwent pulmonary function tests after excluding contraindications，including prebronchodilator pulmonary function tests，bronchodilation ，and post-bronchodilator pulmonary function tests.We measured both prebronchodilator and post-bronchodilator forced expiratory volume in 1s（FEV1），forced expiratory volume in 6 s（FEV6），peak expiratory flow（PEF）and vital capacity（FVC）.The individuals with a post-bronchodilator airway limitation were examined by chest radiography.The pulmonary function was tested by a portable spirometer by the method of forced expiratory volume（deep inhalation，flow-volume curve）.Chest radiography was conducted at the local secondary and above hospitals and was read in parallel by two chest doctors from the provincial hospitals.All data collection and review processes were completed through an electronic questionnaire or on an information collection management platform.

In order to ensure the reliability of the data，the NCNCD center，China CDC has developed a strict quality control protocol for all aspects of the surveillance.A three-level quality control system was established for the national，provincial and county/district，which implemented strict quality control in all aspects of pre-investigation preparation stage，the investigation stage，and data review，clean and analysis after the investigation.National teachers trained 342 provincial teachers and 250 technical backbones in surveillance counties/districts.Provincial teachers trained more than 1，800 staff in surveillance counties/districts，and the training pass percentage was 100%.The provincial CDC conducted on-site supervision and technical guidance to the county/district under its jurisdiction，and the provincial supervision rate reached 100%.The NCNCD center，China CDC conducted supervision and strengthened training in the first surveillance county/district in all provinces，providing special technical support to provinces and county/district to address their difficulties and problems，and helping some provinces such as Tibet to carry out training，etc.The NCNCD center，China CDC completed on-site supervision and intensive training at 42 counties/districts in 31 provinces.The investigation tools and standards were unified.The on-site investigation process，the pulmonary function test operation，and the quality control standards were strictly followed.For spirometry results，we used a quality grade（A，B，C，D，F）based on acceptable manoeuvres and repeatability of FEV1 and FVC.The provincial quality assessment team was responsible for the grading evaluation of all pulmonary function tests in the province，requiring that the A-level test of each county/district was not less than 70%，the A，B or C-level test were not less than 95%，and the final grading rate reached 100%.The National quality assessment team randomly selected 5% pulmonary function gradings to evaluate.The NCNCD Center，China CDC developed the data cleansing and analysis protocol.The two groups of personnel cleaned up the data in parallel.If they found the problems，they would communicate with the provincial CDC and the counties/districts in time to check the data and correct the errors.

A total of 75，107 individuals were interviewed in the 125 counties/districts，and 69，933 and 68，984 have completed prebronchodilator and post-bronchodilator pulmonary function tests，respectively.Among which，66，752 participants’ pulmonary function tests reached Level of A，B，or C，and the qualified rate，i.e.，the rate of A，B or C-level，reached 96.8%.