Effect of different cold air intensities and their lagged effects on outpatient visits for respiratory illnesses in Handan in different seasons

Xinsn Zn , , , Guiqin Fu , , , , Lin Zo , , Ji Wn , Cimn Lin , Junui Wn ,Mn Li

a Handan Meteorological Bureau, Handan, China

b Hebei Meteorological Service Center, Shijiazhuang, China

c Key Laboratory of Meteorology and Ecological Environment of Hebei Province, Shijiazhuang, China

d State Key Laboratory of Numerical Modeling for Atmosphere Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

e Beijing Municipal Climate Center, Beijing Meteorological Bureau, Beijing, China

f Key Laboratory of Meteorological Disaster, Ministry of Education/ Joint International Research Laboratory of Climate and Environment Change/ Collaborative

Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, China

g China Meteorological Administration Xiong’an Atmospheric Boundary Layer Laboratory, Xiong’an New Area, China

h Guangdong Climate Center, Guangzhou, China

Keywords:

ABSTRACT The authors analyzed cold air processes of different intensities and their effect on the number of patients with respiratory illnesses visiting a hospital outpatient department in Handan City in different seasons from 2016 to 2019.For cold air events of the same intensity (apart from cold waves), the number of patients with respiratory illnesses visiting the outpatient department was highest in winter.During the cold waves, the number of patients increased sharply to greater than 55 patients per day, and the number of patients was higher in spring than in autumn.The probability density of the number of patients with respiratory illnesses visiting the outpatient department gradually changed to a positive skewness as the cold air intensity increased.Although the incidence of respiratory illnesses was the highest in winter and lowest in summer, the impact of cold air on respiratory illnesses was the largest in summer and spring, when the number of people with respiratory illnesses visiting the outpatient department increased by 18.4% and 13.3% two and five days after a cold air day.By contrast, the number people visiting the outpatient department with respiratory illnesses in winter only increased by 3.2%three days after a cold air day.The lag time of the health impact decreased with increasing cold air intensity in summer, autumn and winter, whereas the lag time was always long in spring.These findings provide a targeted basis for a scientific response to the risks to human health caused by global climate change.

1.Introduction

The World Health Organization reports that the number of deaths caused by climate warming alone exceeds 100 000 each year, and without effective improvement in climate change, it is expected that 300 000 people will die worldwide each year by 2030 because of climate warming ( McMichael and Lindgren, 2011 ).Extreme events such as heat waves and cold waves not only significantly increase the risk of developing respiratory diseases, but also pose a serious threat to human safety( Guo et al., 2018 ).Numerous studies have shown that temperature and its fluctuations have a certain impact on the incidence and mortality of respiratory diseases.Respiratory illnesses can be induced or aggravated by changes in the weather ( Liu and Zhang, 2005 ), with temperature being a major influencing factor.The human body can adapt to the temperature of the external environment, but large changes in this external temperature can disrupt the mechanisms regulating heat balance, affecting the nervous and endocrine systems, which, in turn, can lead to breathing difficulties ( Wang et al., 2009 ; Geng et al., 2015 ).Le et al.(2018) showed that there was a high incidence of respiratory illness in the winter months and that the impact of temperature on the incidence of respiratory disease was mainly a result of the hysteresis effect of low temperatures.During cold air events, the number of visits to hospitals varies greatly, and there is a lagged effect ( Zhang et al.,2016 ; Wu et al., 2018 ).The relationship between temperature and morbidity or death in human populations presents either a J- or U-shaped distribution.Morbidity or death is the lowest at moderate temperatures;however, morbidity or death tends to increase as the temperature either increases or decreases ( Liu et al., 2014 ; Ma et al., 2016 ; Wu et al., 2021 ).

Respiratory illnesses have pronounced seasonal characteristics( Fu et al., 2019 ).Cold air processes occur throughout the year, and they have different effects on the human body in different seasons.For example, an influx of cold air during a hot summer may make us feel more comfortable, whereas in the transition seasons of spring and autumn an influx of cold air may change us from feeling comfortable to uncomfortable.In winter, cold air increases both discomfort and the risk of disease.We therefore need to consider the impact of different intensities of cold air on respiratory illnesses in different seasons.

Recent decades have produced much research on climate change trends in the Northern Hemisphere and their impact on human health.China will face increasing health risks in the future as a result of climate change, exacerbated by rapid economic development and an aging population ( Chen et al., 2022 ; Cai et al., 2021 ; Dong et al., 2022 ; Zhao et al.,2022 ).Research on weather and respiratory illnesses is mainly based on temperature, the difference in temperature between daytime and nighttime, and the apparent temperature ( Zhang et al., 2020 ; Feng et al.,2020 ; Chen et al., 2021 ; Tan et al., 2019 ).However, few studies have specifically considered the impact of different intensities of cold air in different seasons on respiratory illnesses.We therefore investigated the impact of different intensities of cold air on respiratory illnesses in different seasons with the aim of providing a scientific basis for targeted services for different populations ( Li et al., 2008 ).

2.Data and methods

2.1.Data

We used a dataset of daily outpatient visits for respiratory illnesses at Handan Central Hospital, a large tertiary hospital, between 1 January 2016 and 31 December 2019.The dataset utilized in this study has been sourced from the Municipal Health Commission.It has undergone rigorous data quality control procedures to ensure accuracy and reliability.The dataset encompasses all relevant factors that contributed to the medical visits under investigation, comprising a total of 162 514 cases.The dataset includes the time of the visit, the number of patients, and the category of illness –mainly asthma, pneumonia, colds, or bronchitis.The dataset is highly representative of the trends and patterns of respiratory illnesses in the region.Our study also included meteorological data for the same period sourced from the China Meteorological Data Service Centre ( http://data.cma.cn/site/index.html ).The meteorological data include the three-hourly minimum temperature (°C) and the daily minimum temperature (°C).The decreases in temperature within 24, 48, and 72 h ( ΔT24, ΔT48, and ΔT72) are also included in the dataset.The three-hourly minimum temperature is the minimum temperature in the past three hours.The daily minimum temperature refers to the minimum temperature recorded between 1400 LST on the previous day and 1400 LST on the current day.“ΔT24” represents the calculation of the difference between the daily minimum temperature of the previous day and the current day.Similarly, “ΔT48” and “ΔT72” are calculated in acomparable manner, considering the difference in daily minimum temperature between 48 and 72 h prior to the current day, respectively.T24m,T48m, andT72mare the lowest temperatures within 24, 48, and 72 hours, respectively.

Table 1 Definitions of the different grades of cold air.

2.2.Methods

Using the operational standards of the Central Meteorological Observatory as the basis for distinguishing the process of cold air ( Zhou et al.,2017 ), and referring to relevant literature to determine the classification standards for cold air ( Li et al., 2016 ; Wang, 2017 ), we divided the cold air processes affecting Handan into four grades: weak cold air, moderate cold air, strong cold air, and a cold wave.Table 1 shows the specific classification indicators.A cold air day was defined as the date when the cold air standard was reached.

The statistical process treated a continuous cold air process as a single process.For example, if the daily minimum temperature reached the weak cold air standard on two consecutive days, then it was recorded as a weak cold air process.The statistical processes for other grades of cold air process were similar.According to the classification standard of cold air, the number of patients with respiratory disease under the influence of different levels of cold air was classified and counted.We compared the impact of different levels of cold air processes on respiratory illnesses in the same season and with the same lag time with the impact of no cold air process by using the Case Control study method.

3.Results

3.1.Correlation of 48-h temperature changes with the number of hospital visits

From 2016 to 2019, the 48-h temperature change range in Handan City showed a normal distribution withμ= 1.03 andσ= 2.76 ( Fig.1(a) ).A decrease in temperature greater than 4°C was recorded on an average of 51.5 days per year.We counted the number of people who visited the hospital as outpatients on days when the temperature decreased by greater than 4°C and recorded this by season.When the decrease in temperature was in the range 4°C–7°C, the number of outpatient visits increased in spring, summer, and autumn as the amount of decrease in temperature increased, but decreased in winter ( Fig.1(b) ).By contrast,when the decrease in temperature was in the range 7°C–8°C, the number of outpatients decreased in all seasons.The number of outpatient visits increased in all seasons when the decrease in temperature was greater than 8°C.

There were 206 cold air processes in Handan City between 2016 and 2019, of which 137 were weak cold air processes, 50 were moderate cold air processes, 15 were strong cold air processes, and 4 were cold wave events.Cold air processes occurred most frequently in autumn (64 days;31.1%) and spring (62 days; 30.1%) than in winter (53 days; 25.7%) and summer (27 days; 13.1%).The corresponding incidences of respiratory illnesses in spring, summer, autumn, and winter accounted for 24.9%,21.4%, 23.0%, and 30.7% of the total incidence, respectively.

Fig.1.Characteristics of temperature change range and the corresponding number of outpatient visits for respiratory illnesses in Handan from 2016 to 2019, and the probability distribution of the number of outpatient visits at different cold air intensities.(a) Frequency diagram and probability density function (PDF) of outpatient visits under different decreases in temperature.(b) Average number of outpatient visits in different seasons.(c–f) The probability distribution of the number of outpatient visits at weak cold air, moderate cold air, strong cold air, and cold waves, respectively.

The number of people with respiratory illnesses attending hospital as outpatients was counted based on the classification standard for cold air.Under the influence of weak cold air ( Fig.1(c) ), moderate cold air( Fig.1(d) ), strong cold air ( Fig.1(e) ), and cold waves ( Fig.1(f) ), the corresponding probabilities were the highest when the numbers of outpatients were 45, 55, 45, and 55, with 35.8%, 36%, 46.7%, and 75%,respectively.With an increase in the intensity of cold air, the variation in the number of patients with respiratory illnesses decreased.Moderate cold air presented a negatively skewed distribution, while other intensity cold air presented a positively skewed distribution.

Our analysis shows that cold air frequently occurs in Handan City,with the highest frequency in autumn and spring and the lowest frequency in summer.The impact of different intensities of cold air on the number of outpatient visits showed that, with an increase in cold air intensity, the number of visits was positively skewed, with the number of high-probability visits gradually shifting to the right and an increase in the probability of a large number of visits.The average daily number of outpatient visits was concentrated during cold waves when it was greater than 55 per day, higher than the probability distribution of the number of visits at other intensities of cold air.This also shows that the cold wave standard defined by meteorology has indicative significance for risks to human health.

3.2.Time series characteristics of cold air and respiratory illnesses

The overall number of cold air processes showed a decreasing trend from 2016 to 2019, with a maximum of 61 cold air processes in 2016 and a minimum of 44 in 2019.The number of outpatients and the temperature fluctuated periodically in inverse phase when the cold air was affected ( Fig.2 ).The number of outpatients was the highest in winter when the temperature was low, but the lowest in summer when temperature was high.The highest number of outpatient visits (58.2) was recorded in 2018, corresponding to an average temperature of 4.9°C.The lowest number of outpatient visits (50.3) was recorded in 2017, corresponding to an average temperature of 6.6°C.This shows that there were more outpatient visits when temperatures were lower.

The average decrease in temperature in 2018 was 5.9°C, whereas the average decrease in temperature in 2017 was 6.6°C.When the amount of decrease in temperature increased in summer, the daily number of outpatient visits increased (a positive phase change), whereas when the amount of decrease in temperature increased in winter, the daily number of outpatient visits decreased (a negative phase change).Spring is a season of transition from cold to warm and both the amount of decrease in temperature and the daily number of outpatient visits gradually changed from a negative phase to a positive phase.Autumn is a transitional season from warm to cold and the decrease in temperature and the daily number of outpatient visits were first in a positive phase and then gradually changed to a negative phase.

Fig.2.Time series of the (a) number of daily outpatient visits, (b) daily minimum temperature (units: °C), and (c) decrease in temperature (units: °C) during cold air processes in Handan from 2016 to 2019.The blue, red, yellow, and black sections of the lines represent spring, summer, autumn, and winter, respectively.

This analysis shows that the daily number of outpatient visits by patients with respiratory illnesses is not only related to temperature( Wang, 2013 ), but also to the amount of decrease in temperature –that is, there are more visits to outpatients by people with respiratory illnesses when the temperature is lower or there is a larger decrease in temperature.However, because the temperature varies with the season, cold air has different effects on people with respiratory illnesses in different seasons.In warm seasons, the daily number of people affected by cold air increases with larger decreases in temperature, showing that more intense cold air on a warming day affects more people.By contrast, in cold seasons when temperatures are low, the daily number of people affected by cold air decreases with larger decreases in temperature, showing that more intense cold air on a decrease in temperature day affects fewer people.This is seen as a lagged effect of cold air.

3.3.Seasonal characteristics and effects of cold air and respiratory illnesses

Table 2 shows that on the day when the cold air was affected, the incidence of respiratory illnesses in Handan City is high in winter and low in summer.The number of outpatient visits affected by different intensities of cold air varies with the season.The number of outpatient visits increases with the intensity of cold air in spring and summer; the correlation coefficient in spring reaches 0.95 and passes the significance test of 0.05.In spring, the number of outpatients increases by 7.5% under the influence of a cold wave than when there is no cold air.In summer, the number of outpatients increases by 10% under the influence of moderate cold air than when there is no cold air.However, in winter,the number of outpatients decreases with an increase in the cold air intensity; the correlation coefficient reaches - 0.83 but does not pass the significance test of 0.05.The range in the number of outpatient visits decreases with increasing cold air intensity, indicating that the number of medical visits tend to stabilize when the cold air intensity is stronger.

The same intensity of cold air could have different effects depending on the season.When the cold air intensity is weak, more patients are treated at lower temperatures.When the cold air intensity is moderate or strong, more patients are treated at lower temperatures in spring,summer and winter.Cold waves led to more people visiting outpatients at higher temperatures.As a result of the low number of occurrences,the impact of cold wave processes needs to be studied further.

Table 2 The number of outpatient visits and the decrease in temperature (units: °C) on the day when the cold air affects in different grades of cold air in different seasons.“None ”, “Weak ”, “Moderate ”, “Strong ”, and “Wave ”represent no cold air, weak cold air, moderate cold air, strong cold air, and cold wave, respectively.

Table 3 Under the influence of different grades of cold air in different seasons on respiratory disease, the maximum percentage increase in the number of patients and its corresponding lag time in days.“Weak ”, “Moderate ”, “Strong ”, “Wave ”, and “All ”represent weak cold air, moderate cold air, strong cold air, cold wave, and all cold air, respectively.

3.4.Hysteresis effect of cold air on respiratory illnesses in different seasons

The impact of cold air processes on human health is influenced by both the intensity of the cold air outbreak and the baseline temperature.Furthermore, this impact exhibits a hysteresis effect.To investigate this phenomenon, we conducted an analysis to examine the occurrence of various grades of cold air across different seasons.The results of this analysis can be found in Table 3.

The impact of cold air on respiratory diseases shows a lagged effect in different seasons.The overall lag time is longer in spring and shorter in summer and is between these two values in autumn and winter.The impact of cold air on respiratory illness is more remarkable in summer and spring than in autumn and winter.Among them, the number of outpatient visits for respiratory illnesses increases by 18.4% for all cold air at a lag time of two days in summer.

The number of outpatient visits increases with the intensity of cold air in different seasons; after the effect of a cold wave in spring, the number of outpatient visits increases by 48.5%.The lag time shortens with increasing cold air intensity in summer, autumn, and winter, whereas the lag time is always long in spring.

4.Discussion and conclusions

By analyzing the probability of the impact of different intensities of cold air on the number of outpatient visits, we found that with an increase in cold air intensity, the number of outpatients showed a positively skewed trend –that is, the probability of increasing numbers of outpatient visits and the average daily number of outpatients was higher during cold waves (greater than 55 outpatient visits per day) than for other cold air intensities.The cold wave standard defined by the meteorological conditions therefore has particular indicative significance for risks to human health.

Cold air processes are common in Handan City in spring and autumn,followed by winter, with the lowest number occurring in summer.The incidence of respiratory illness is high in winter, followed by spring and autumn, and lowest in summer.

On the day when the cold air affects, the number of outpatient visits impacted by different intensities of cold air varies across seasons.The number of outpatient visits increases with the intensity of cold air in spring and summer.However, in winter, the number of outpatients decreases with an increase in the cold air intensity.

The impact of cold air on respiratory diseases shows a lagged effect in different seasons.The lag time shortens with increasing cold air intensity in summer, autumn, and winter, whereas the lag time is always long in spring; the overall lag time is longer in spring and shorter in summer.The impact of cold air on respiratory illness is more remarkable in summer and spring; the number of outpatient visits increases with the intensity of cold air.

The research results of this article are in good agreement with the findings of other regional studies ( Le et al., 2018 ; Wang et al., 2016 ),from the perspective of the impact and lagged effect of temperature and its changes on the number of visits for respiratory diseases in Handan City.The main manifestation of the impact of temperature on the incidence of respiratory diseases is that the incidence rate is low in summer and high in winter.This phenomenon can be attributed to various factors.Firstly, in winter, indoor cross-infection becomes more prevalent owing to closer proximity and reduced ventilation, facilitating the spread of respiratory illnesses.Secondly, the adverse effects of low temperatures on the immune system and respiratory system makes individuals more susceptible to respiratory diseases.Additionally, low temperatures contribute to the survival of bacteria in droplets, increasing the risk of infection transmission.Collectively, these factors contribute to a rise in both the incidence and mortality rates of respiratory diseases ( Allegra et al., 2002 ).The impacts of a decrease in temperature in Handan City on the number of visits for respiratory diseases show instant effects in summer and lagged effects in spring, and the impacts in both seasons are relatively large.Despite the similarity in average temperatures between spring and autumn, the impact and lagged effect of cold air in spring are greater than those in autumn.This is because the phagocytic function of alveolar macrophages, which is crucial for clearing bacteria, decreases during the winter months, significantly reducing their ability to eliminate bacteria.During the autumn recovery period,from the warm to cold season, the body’s immune system is in a weakened state.Therefore, the human immune system is more sensitive in autumn than in spring, making the impact of autumn cold air stronger than that of spring.Respiratory illnesses are also related to genetics,physique, lifestyle, and health awareness.However, the time series of the dataset used in this research is relatively short and more data are needed to more fully reflect the impact of cold air on respiratory illnesses.Our analysis also needs to be improved by considering different age groups.

These research findings indicate that the impact of cold air on respiratory diseases in the Handan region exhibits notable seasonal variations and lagged effects.Therefore, it is necessary to take appropriate precautionary measures based on the impact of different intensities of cold air in different seasons –especially spring and summer.

Funding

This study was supported by the Strategic Priority Research Program of Chinese Academy of Sciences [grant numbers XDA23090102 ], the National Natural Science Foundation of China [grant numbers 42175078 and 42075040 ], the Health Meteorological Project of Hebei Province[grant number FW202150 ], and the National Key Research and Development Program of China [grant number 2018YFA0606203 ].

Acknowledgments

We sincerely thank the reviewers, whose valuable suggestions helped us to improve our manuscript.We also thank Handan Central Hospital for the respiratory diseases dataset, and the Meteorological Information Sharing Platform of Hebei Province for the meteorological data.