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Preplanned Studies: The Combined Effects of High Temperatures and Ozone Pollution on Medical Emergency Calls — Jinan City, Shandong Province, China, 2013–2019

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  • Summary

    What is already known about this topic?

    Studies have extensively documented the separate and independent effects of extreme temperature and ozone on morbidity and mortality associated with respiratory and circulatory diseases.

    What is added by this report?

    The study revealed a significant association between elevated temperature, ozone pollution, and the combined effect of high temperature and ozone pollution with an increased risk of all-cause medical emergency calls (MECs) and MECs specifically related to neurological diseases.

    What are the implications for public health practice?

    Interventional measures should be implemented to mitigate exposure to high temperatures and ozone levels. Specifically, during the warm season, it is crucial for relevant authorities to focus on disseminating scientific information regarding the health impacts of elevated temperatures and ozone pollution. Additionally, timely public health advisories should be issued to alert the public effectively.

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  • Funding: Big-data Research Project of Jinan Health Committee; Special Project of Public Health Plan of Jinan Health Committee
  • [1] Cheng J, Xu ZW, Bambrick H, Prescott V, Wang N, Zhang YZ, et al. Cardiorespiratory effects of heatwaves: a systematic review and meta-analysis of global epidemiological evidence. Environ Res 2019;177:108610. http://dx.doi.org/10.1016/j.envres.2019.108610CrossRef
    [2] Wang YQ, Wang K, Cheng WL, Zhang YQ. Global burden of chronic obstructive pulmonary disease attributable to ambient ozone in 204 countries and territories during 1990-2019. Environ Sci Pollut Res Int 2022;29(6):9293-305. http://dx.doi.org/10.1007/s11356-021-16233-yCrossRef
    [3] Zhang Y, Tian QQ, Feng XY, Hu WD, Ma P, Xin JY, et al. Modification effects of ambient temperature on ozone-mortality relationships in Chengdu, China. Environ Sci Pollut Res Int 2022;29(48):73011-9. http://dx.doi.org/10.1007/s11356-022-20843-5CrossRef
    [4] Chen C, Liu J, Shi WY, Li TT, Shi XM. Temperature-modified acute effects of ozone on human mortality—Beijing municipality, Tianjin municipality, Hebei province, and surrounding Areas, China, 2013-2018. China CDC Wkly 2021;3(45):964-8. http://dx.doi.org/10.46234/ccdcw2021.234CrossRef
    [5] Cui LL, Conway GA, Jin L, Zhou JW, Zhang J, Li XW, et al. Increase in medical emergency calls and calls for central nervous system symptoms during a severe air pollution event, January 2013, Jinan City, China. Epidemiology 2017;28 Suppl 1:S67-73. http://dx.doi.org/10.1097/EDE.0000000000000739.
    [6] Pintarić S, Zeljković I, Pehnec G, Nesek V, Vrsalović M, Pintarić H. Impact of meteorological parameters and air pollution on emergency department visits for cardiovascular diseases in the city of Zagreb, Croatia. Arh Hig Rada Toksikol 2016;67(3):240-6. http://dx.doi.org/10.1515/aiht-2016-67-2770CrossRef
    [7] Ding PH, Wang GS, Guo YL, Chang SC, Wan GH. Urban air pollution and meteorological factors affect emergency department visits of elderly patients with chronic obstructive pulmonary disease in Taiwan. Environ Pollut 2017;224:751-8. http://dx.doi.org/10.1016/j.envpol.2016.12.035CrossRef
    [8] Pryor WA, Squadrito GL, Friedman M. A new mechanism for the toxicity of ozone. Toxicol Lett 1995;82-83:287-93. http://dx.doi.org/10.1016/0378-4274(95)03563-XCrossRef
    [9] Appenheimer MM, Evans SS. Temperature and adaptive immunity. Handb Clin Neurol 2018;156:397-415. http://dx.doi.org/10.1016/B978-0-444-63912-7.00024-2CrossRef
  • FIGURE 1.  Spearman correlation analysis between temperature, O3, and MECs in Jinan from May to September 2013–2019. (A) represents the correlation analysis between O3 and temperature; (B) represents the correlation analysis between temperature and MECs; (C) represents the correlation analysis between O3 and MECs.

    FIGURE 2.  The lag effects of temperature, ozone (O3), and their combined effects on all-cause morbidity and morbidity rates for various systemic diseases during the warm season in Jinan from 2013 to 2019.

    Note: The variable “Temperature+O3” in this study represents the combined impact of high temperature and ozone pollution.

    Abbreviation: OR=odds ratio; CI=confidence interval; MECs=medical emergency calls.

    TABLE 1.  Daily levels of air pollutants, meteorological factors, and MECs in Jinan City from 2013 to 2019.

    VariablesMean±SDMinP25P50P75Max
    Air pollution (μg/m3)
    PM1057.09±28.723365173196
    PM2.5114.83±51.03579106141348
    NO238.13±12.56929364588
    SO230.09±22.886142439182
    CO969.75±324.513637359101,1162,598
    O3154.67±47.8730122157187266
    Meteorological factor
    Temperature (℃)30.38±4.0615.627.930.933.339.9
    Wind speed (m/s)2.36±1.020.41.72.12.87.7
    Relative humidity (%)61.34±17.371549627498
    Pressure (hPa)988.53±5.189759859879921,004
    Medical emergency calls (calls/day)
    All-cause258±40161230252278395
    Respiratory diseases19±9211182544
    Cardiovascular diseases35±10628354263
    Neurological diseases39±81533394478
    Abbreviation: MECs=medical emergency calls; SD=standard deviation; Min=minimum; P25=25th percentile; P50=50th percentile; P75=75th percentile; Max=maximum.
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The Combined Effects of High Temperatures and Ozone Pollution on Medical Emergency Calls — Jinan City, Shandong Province, China, 2013–2019

View author affiliations

Summary

What is already known about this topic?

Studies have extensively documented the separate and independent effects of extreme temperature and ozone on morbidity and mortality associated with respiratory and circulatory diseases.

What is added by this report?

The study revealed a significant association between elevated temperature, ozone pollution, and the combined effect of high temperature and ozone pollution with an increased risk of all-cause medical emergency calls (MECs) and MECs specifically related to neurological diseases.

What are the implications for public health practice?

Interventional measures should be implemented to mitigate exposure to high temperatures and ozone levels. Specifically, during the warm season, it is crucial for relevant authorities to focus on disseminating scientific information regarding the health impacts of elevated temperatures and ozone pollution. Additionally, timely public health advisories should be issued to alert the public effectively.

  • 1. Department of Scientific Research and Education, Jinan Municipal Center for Disease Control and Prevention, Jinan Municipal Center for Disease Control and Prevention Affiliated to Shandong University, Jinan City, Shandong Province, China
  • 2. Jinan Health Well Development Center, Jinan City, Shandong Province, China
  • 3. Department of Environmental Health, Jinan Municipal Center for Disease Control and Prevention, Jinan City, Shandong Province, China
  • 4. Department of Emergency, Jinan Medical Emergency Center, Jinan City, Shandong Province, China
  • Corresponding author:

    Liangliang Cui, cll602@163.com

  • Funding: Big-data Research Project of Jinan Health Committee; Special Project of Public Health Plan of Jinan Health Committee
  • Online Date: January 12 2024
    Issue Date: January 12 2024
    doi: 10.46234/ccdcw2024.007
  • Epidemiological evidence demonstrates the significant impact of high temperature on both short-term and long-term health outcomes, resulting in increased morbidity and mortality rates for respiratory and circulatory diseases, among other health conditions (1). Simultaneously, there is a growing concern about ozone (O3) pollution, which poses a pressing challenge to urban development (2). Numerous studies have established a strong association between O3 pollution and the onset and progression of respiratory and circulatory diseases (34). However, there is still a research gap concerning the combined effects of these two variables. Recently, there has been a growing interest in using medical emergency calls (MECs) as indicators to explore the acute effects of high temperature and O3 pollution (57). Addressing this research gap, our study focuses on Jinan City, Shandong Province, China, as a representative urban area grappling with the dual challenge of high temperature and O3 pollution. We employed a time-stratified case-crossover study design to estimate the impacts of high temperature and O3 pollution on MECs. The results indicate that high temperature, O3 pollution, and their combination significantly increase the risk of all-cause MECs and MECs specifically related to neurological diseases. These findings provide essential information for the development of future measures to reduce exposure to high temperature and O3 pollution. Moreover, emphasizing the necessity to consider the combined effects of high temperature and O3 pollution is crucial for addressing emerging public health concerns.

    For this research study, we collected daily data from the MECs of the Jinan Medical Emergency Center (JMEC) website (http://www.jn120.cn/). The data were collected from May 1 to September 30 for the years 2013–2019. There were minor fluctuations in the MECs rate during the study period, as shown in Supplementary Table S1. The information obtained from the MECs included the patient’s call time, primary statement, and preliminary diagnosis. The primary statement information referred to the main signs and symptoms provided during the telephone call, while the preliminary diagnosis information indicated the disease diagnosis given when the patient was admitted to the hospital’s emergency department. JMEC oversees 66 first-aid service stations that are affiliated with hospitals, providing coverage across all ten administrative districts of Jinan City, as shown in Supplementary Table S2. To classify the MECs, we used the International Classification of Diseases, 10th revision (ICD-10). We specifically screened for ICD-10 codes J00–J99, which are associated with respiratory diseases, I00–I99, which are related to circulatory diseases, and G00–G99, which pertain to neurological diseases.

    Meteorological data collected daily throughout the study period were provided by the China Meteorological Science Data Sharing Service Network (http://data.cma.gov.cn/). This data included the daily mean maximum temperature (℃), relative humidity (%), pressure (hPa), and wind speed (m/s). The daily air pollutant data, such as fine particulate matter (PM2.5), particulate matter (PM10), nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO), and 8-hour ozone (O3-8h, abbreviated as O3), were obtained from the Jinan Ecological Environmental Protection Bureau. For this study, we determined the daily pollutant concentration level in Jinan by averaging the readings from all monitoring stations.

    In the initial stage of our analysis, we began with a descriptive examination of the compiled data using various indicators, including mean, standard deviation, minimum, maximum, median, first quartile, and third quartile. Following this, correlation analysis was conducted to explore the relationship between temperature, ozone concentration, and MECs, as well as the associations between air pollutants and meteorological factors. Subsequently, a time-stratified case-crossover study design in combination with a conditional logistic regression model was employed to investigate the acute impacts of temperature and ozone pollution on MECs. Detailed information and sensitivity analyses for this core model can be found in the Supplementary Material. Based on a comprehensive review of previous studies and our analytical results, we selected a five-day period for our lag effect study. We examined the effects on the current day (Lag0), single-day lag effects (Lag1–Lag5), and cumulative lag effects (Lag01–Lag05) on MECs to identify the most impactful day and estimate the effect. The effect estimates were presented as odds ratios (ORs) along with their corresponding 95% confidence intervals (CIs). To address diseases with high sensitivity, a subgroup analysis focusing specifically on respiratory, circulatory, and neurological diseases was conducted. The R software (version R 4.2.0; R Studio Inc; the USA) was used for the analysis of time-stratified cross-case data. Statistical significance was considered at a P-value of less than 0.05.

    Table 1 presents the daily levels of air pollutants, meteorological factors, and MECs in Jinan from 2013 to 2019. The total number of MECs recorded during this period was 275,868, with an average daily number of all-cause MECs at 258±40 cases. Among these cases, the number of MECs related to respiratory, circulatory, and neurological diseases were 19±9, 35±10, and 39±8, respectively. Furthermore, the average maximum daily temperature reached 30.38±4.06 ℃, while the daily concentration of O3 was 154.67±47.87 μg/m³.

    VariablesMean±SDMinP25P50P75Max
    Air pollution (μg/m3)
    PM1057.09±28.723365173196
    PM2.5114.83±51.03579106141348
    NO238.13±12.56929364588
    SO230.09±22.886142439182
    CO969.75±324.513637359101,1162,598
    O3154.67±47.8730122157187266
    Meteorological factor
    Temperature (℃)30.38±4.0615.627.930.933.339.9
    Wind speed (m/s)2.36±1.020.41.72.12.87.7
    Relative humidity (%)61.34±17.371549627498
    Pressure (hPa)988.53±5.189759859879921,004
    Medical emergency calls (calls/day)
    All-cause258±40161230252278395
    Respiratory diseases19±9211182544
    Cardiovascular diseases35±10628354263
    Neurological diseases39±81533394478
    Abbreviation: MECs=medical emergency calls; SD=standard deviation; Min=minimum; P25=25th percentile; P50=50th percentile; P75=75th percentile; Max=maximum.

    Table 1.  Daily levels of air pollutants, meteorological factors, and MECs in Jinan City from 2013 to 2019.

    The chronological diagram presented in Supplementary Figure S1 visually demonstrates consistent trends and potential relationships among temperature, O3 concentration, and MECs. Additionally, the Spearman correlation analysis (Figure 1) indicates statistically significant correlations between these variables during the study period. Specifically, temperature and MECs, O3 concentration and MECs, and temperature and O3 concentration exhibited significant correlations. Notably, a strong positive correlation was observed between O3 concentration and temperature (r=0.63, P<0.05). Further details on the correlation results between air pollutants and meteorological factors are provided in Supplementary Table S3.

    Figure 1. 

    Spearman correlation analysis between temperature, O3, and MECs in Jinan from May to September 2013–2019. (A) represents the correlation analysis between O3 and temperature; (B) represents the correlation analysis between temperature and MECs; (C) represents the correlation analysis between O3 and MECs.

    Figure 2 presents an analysis of the single-day lag effect concerning temperature, O3 pollution, and their combined impact. Statistically significant independent effects of both temperature and O3 pollution on all-cause MECs were noted from Lag0 to Lag3, with the most pronounced effect occurring at Lag0. The OR values for temperature and O3 pollution were 1.013 (95% CI: 1.010, 1.015) and 1.0005 (95% CI: 1.0002, 1.0006), respectively. Notably, the combined influence of temperature and O3 pollution demonstrated statistical significance from Lag0 to Lag5, peaking at Lag0, with an OR of 1.017 (95% CI: 1.010, 1.024). A trend of marginal decline in OR values was observed for both independent and combined effects of temperature and O3 pollution with progressing Lag days. Additionally, subgroup analysis indicated significant impacts on MECs for neurological diseases, with OR values of 1.017 (95% CI: 1.010, 1.024), 1.001 (95% CI: 1.000, 1.002), and 1.022 (95% CI: 1.004, 1.041). However, the effects of MECs on respiratory and circulatory diseases were not statistically significant. The cumulative lag effect analysis of temperature, O3 pollution, and their combined effect is depicted in Supplementary Figure S2.

    Figure 2. 

    The lag effects of temperature, ozone (O3), and their combined effects on all-cause morbidity and morbidity rates for various systemic diseases during the warm season in Jinan from 2013 to 2019.

    Note: The variable “Temperature+O3” in this study represents the combined impact of high temperature and ozone pollution.

    Abbreviation: OR=odds ratio; CI=confidence interval; MECs=medical emergency calls.

    • This study employs a time-stratified case-crossover design to investigate the combined effects of high temperature and O3 pollution on MECs within Jinan City from 2013 to 2019. The results of our analysis confirm that both temperature and O3 pollution independently increase the risk of MECs during the warm season, and their combined influence further escalates this risk. These findings differ somewhat from previous research studies (67). From a pathogenesis perspective, it is understood that both temperature and O3 pollution can contribute to the development and occurrence of various respiratory, circulatory, and neurological disorders. This may occur through mechanisms such as inflammation and immune dysregulation. However, it is important to consider that regional disparities in weather conditions (such as temperature, humidity, and wind speed), demographic characteristics of the at-risk population, the composition of O3 pollution sources, and the range of O3 concentrations could account for the observed discrepancies. Additionally, variations in exposure durations and statistical analysis models may also play significant roles in explaining the differences encountered.

      The results of the stratified analysis indicate that both temperature and O3 pollution have a positive influence on neurological disorders in residents. This can be attributed to the reactive nature of O3, an oxidant and reactive oxygen species. When inhaled, O3 reacts with proteins and lipids, leading to the production of denatured proteins/lipids, carbon/oxygen free radicals, and toxic compounds. This triggers an oxidative stress response in lung macrophages, resulting in physiological disruptions (8). Additionally, higher temperatures exacerbate this issue by promoting immune cell activation and transition, leading to various immune adaptations that contribute to the development of neurological diseases (9). Interestingly, surface-level O3 formation rates are closely linked to temperature, suggesting potential reciprocal influences between O3 pollution and climate change. Therefore, the combination of these factors has a significant impact on population health. However, previous studies have primarily focused on the independent effects of meteorological factors or air pollution on neurological diseases. Hence, this study’s examination of the combined implications of temperature and O3 pollution on neurological diseases is of utmost importance. It is recommended that future research further investigates the risks associated with temperature and O3 pollution on various neurological disorders, while also considering disease-specific sensitivities.

      In our stratified analysis, we have also found that the combined effect of warm season temperature and ozone pollution on emergency calls for respiratory and circulatory diseases was not statistically significant. This finding contradicts previous research (67). The apparent discrepancies in research outcomes might be attributed to variations in research design methodologies, geographic differences in warm season temperature ranges and levels of O3 pollution, as well as variations in the characteristics of the study populations, all of which may influence the direction of the study’s impact.

      However, this study has several limitations that should be considered. Firstly, the use of urban monitoring data averages to represent individual exposure levels may introduce variability into the estimates of combined effects on study outcomes. Secondly, the study was unable to investigate the susceptibility of different genders and age groups, which could have provided valuable insights into the potential heterogeneity of the effects. Thirdly, it should be noted that this study assumes Jinan City is representative of other cities, and outcomes may differ in cities with diverse geographical locations and climate patterns. Lastly, since the COVID-19 epidemic in 2020, the disease composition of MECs has changed significantly, so this study only analyzes data up to 2019.

      In conclusion, there was a significant rise in heat-related morbidity cases among residents due to the combined impact of high temperature and O3 pollution. Of particular concern were the increased incidences of neurological disorders associated with these environmental factors. These findings highlight the urgent need for increased awareness and action from relevant agencies. During the peak of summer, it is crucial to prioritize the dissemination of scientific knowledge regarding meteorological factors and the health implications of O3 pollution. Specifically, when faced with elevated temperatures and heightened O3 levels, it becomes imperative for authorities to issue public health warnings as a proactive measure in order to reduce potential health risks.

    • All authors had no conflicts of interest.

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