# An Urgent Health Problem of Indoor Air Pollution: Results of a 15-Year Carbon Monoxide Poisoning Study in Jinan City

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We first counted the number of indoor CO poisoning cases and related cases, and then estimated the incidence and death rate in Jinan from 2007 to 2021 overall and by year individually. Furthermore, we described the spatial and temporal characteristics of CO poisoning. In terms of space, we compared the difference between urban and rural districts by drawing a map. In terms of time, we described the prone time of CO poisoning in annual, monthly and hourly distribution, respectively. Finally, we examined the individual risk for CO exposure–disease–death relationship and performed trend matching. The method steps and details as following description:

### Study participants

The study was approved by the Ethics Committees of the School of Public Health, Shandong University (the identification code was LL20220922) and informed consent was obtained from all participants and/or their legal guardians. The study complied with the Declaration of Helsinki.

### Background information of Jinan

Jinan is located at 36.40° N latitude and 110.00° E longitude and covers a total of 8,177.21 km2It is divided into ten administrative districts, including five urban area districts Lixia, Shizhong, Huaiyin, Tianqiao, Licheng and five rural area districts Changqing, Zhangqiu, Jiyang, Pingyin and Shanghai15. It has a moderate monsoon climate with unevenly distributed seasons and the winter season lasting almost 150 days (from November to next March)16. The minimum temperature in winter is often below −10 °C and the extreme weather like cold waves, blizzard sometimes occurred in January and December. According to Jinan Urban Central Heating Management Regulations17central heating services are provided in urban region from March 15 to November 15 (121 days each year), while coal heating is often used in rural and urban-rural common areas due to substandard facilities, which greatly increases the risk of CO poisoning. .

### Data Collection

Daily meteorological data during 2007 to 2021 was provided by China Meteorological Data Sharing Service System network18including daily average temperature, daily maximum temperature and daily minimum temperature.

The daily non-occupational CO poisoning event profiles in Jinan from 2007 to 2021 were obtained from China’s Public Health Emergency Information System19,20. The system runs based on the 91 reportable reporting hospitals and integrated outbreak/event profiles on infectious diseases, foodborne diseases, waterborne diseases, occupational poisoning, environmental emergencies (indoor and outdoor air pollution) and other unknown public health events. Non-occupational CO poisoning event was involved in the indoor environmental emergencies. We collected the viable cases of CO poisoning, including the disease onset date (hospital visit time), poisoning place and location, reason for poisoning, CO exposure population and severity of poisoning.

The main causes of non-occupational CO poisoning in Jinan include household coal heating, gas leakage in catering, suicide and others (caused by other events). From 2007 to 2021, CO poisoning caused by domestic coal heating accounted for 81%, which was the leading cause of CO poisoning. Therefore, spatiotemporal characteristics and occurrence trend of domestic coal heating were analyzed in this study.

### Analysis of epidemiological characteristics

Using descriptive epidemiological methods to analyze the temporal, spatial and population characteristics of CO poisoning caused by domestic coal heating. Exposure rate, incidence density (cases) and death rate were measured using the following formula:

$$\mathrmExposure\, Rate = \frac\mathrmNumber \,of \,CO \,Exposed \,Individuals\mathrm Annual \,Population \,\times \,\mathrm Time \,(\mathrmyears)\,\times\, \mathrm100,000$$

(units: per 100,000 person-years).

$$\mathrmIncidence \,density = \frac\mathrmNumber \,of \,CO \,Poisoning\, Cases\mathrmAnnual\, Population\, \times \,\mathrm Time \,(\mathrmyears)\,\times \,\mathrm100,000$$

(units: per 100,000 person-years).

$$\mathrmMortality\, rate = \frac\mathrmNumber \,of \,CO \,Poisoning \,Deaths\mathrmAnnual \,Population \,\times\, \mathrm Time\, (\mathrmyears)\,\times \,\mathrm100,000$$

(units: per 100,000 person-years).

### Statistical analysis

We set up an Excel database and used descriptive epidemiological methods to analyze the data. The spatial analysis was performed by RStudio version 3.5.1. The statistical analyzes were performed by SPSS 21.0 (SPSS Inc., Chicago, IL, USA). Chi-Square test was used to compare rates, the statistical significance level was set at 0.05.

This study was approved by the Ethics Committees of the School of Public Health, Shandong University (the identification code was LL20220922) and informed consent was obtained from all participants and/or their legal guardians. The study complied with the Declaration of Helsinki.