| BackgroundLower respiratory tract infection（LRTI）is a clinically common respiratory disease,and is mainly caused by the invasion of some pathogenic microorganisms into the lower respiratory tract,alveolar,and other lung structures,leading to some inflammatory reactions.The general symptoms are mainly cough,sputum,fever,chest tightness,and shortness of breath.LRTI includes acute bronchitis,bronchitis,chronic bronchitis,pneumonia,and bronchiectasis.As a common and frequently-occurring disease of the respiratory system,it may occur in any age group,most common in children,the elderly,and the immunocompromised.Relevant studies have shown that admission due to LRTI diseases shows an obvious seasonal trend,with much more admissions in winter and spring than in summer and autumn,indicating that the changes in meteorological factors may be correlated to the incidence of LRTI diseases.Among various meteorological factors,the changes in air temperature have the most significant effect on LRTI disease.The effect of air temperature on human health has a threshold range.When the changes in air temperature exceed the body’s regulatory range,there will be a series of uncomfortable reactions in some people’s body functions,resulting in the occurrence or worsening of LRTI diseases.Most studies in previous literature are limited to some cities in developed countries and eastern China.Inland provinces in northwestern China are rarely involved.And,the relevant study outcome variables mainly are the number of in-patients or admission rate.By contrast,the number of out-patient visits can more sensitively reflect the impact of changes in air temperature on population health,and the sample size is larger,so it has better statistical potency.In addition,with the deepening of relevant research,more and more studies show that the effect of air temperature on the occurrence of LRTI diseases may be caused by the rapid changes in temperature in a short period of time,rather than by the mean daily air temperature itself.Therefore,in recent years,in addition to the mean daily air temperature,some new air temperature indexes,such as diurnal temperature range（DTR）and apparent temperature（AT）,have been widely used to evaluate the effect of the rapid changes in temperature in a short period of time on relevant diseases.The DTR,i.e.,the difference between the daily maximum and minimum air temperatures,is an index that reflects the effect of short-term changes in air temperature on health.AT is obtained from the comprehensive calculation of daily mean air temperature,relative humidity,wind speed,and other meteorological indexes.Compared with traditional temperature change indexes（daily mean air temperature and DTR）,AT can better reflect the human body’s perception of temperature changes in the external environment.At present,there are few studies on the effect of DTR and AT on the number of outpatient visits for LRTI diseases.There are fewer relevant studies in China.Gansu Province is located in inland northwest China with a long and narrow terrain sloping from southwest to northeast and many climate types.It crosses multiple climatic zones from south to north,including climate types such as temperate monsoon climate,temperate continental（arid）climate,semi-arid desert climate,and other climate types.Affected by global warming,in recent 30 years,the air temperature in Gansu Province has shown a prominent rising trend;the frequency of extremely high temperatures has increased.While in winter and spring,influenced by the cold air moving eastward from Xinjiang,the occurrence of extreme cold weather has not shown a significant decrease trend.These weather processes or climatic events may have adverse effects on the health of residents in different parts of Gansu Province.Based on the consideration of the geographical and meteorological conditions,socio-economic development level,and population distribution in Gansu Province,Jiuquan,Dingxi,and Tianshui were selected as representative cities in western,central,and eastern Gansu for research.The correlation between different air temperature indexes（daily mean air temperature,DTR and AT）and the number of out-patient visits for LRTI in these countries was analyzed by the generalized additive model based on Quasi-Poisson distribution combined with distributed hysteresis non-linear model.Besides,the effect of the above-mentioned three air temperature indexes on out-patients for LRTI of different gender and age groups was evaluated,so as to provide a scientific basis for reducing the incidence of LRTI,improve the emergency response capacity of relevant departments to cope with extreme weather,urge residents（especially patients with LRTI or susceptible population）to take preventive measures,and reduce residents’health impairment.MethodsThe data of out-patients who visited hospitals in urban Jiuquan,Dingxi and Tianshui for LRTI from January 1,2018,to December 31,2019,were collected.In addition,the meteorological data（including daily mean temperature,daily maximum temperature,daily minimum temperature,daily relative humidity,daily pressure,and wind speed）and daily air pollutant concentration data(including PM2.5,PM10,SO2,NO2,O38h,and CO)were also collected.The daily AT was calculated with reference to the calculation methods for AT in references.The non-linear correlation and hysteresis effect between the daily mean air temperature,DTR,and AT and the number of out-patient visits for LRTI in each city were analyzed by the generalized additive model based on Quasi-Poisson distribution combined with distributed hysteresis non-linear model.Moreover,stratified analysis was performed by different gender（male and female）,different ages（0-14,15-64,and≥65）,and different seasons（spring,summer,autumn,and winter）.Results1.Descriptive analysis:The total and average daily out-patient visits for LRTI in Jiuquan during 2018-2019 were 65,676 and 90,respectively.The total and average daily out-patient visits for LRTI in Dingxi were 45,223 and 62,respectively.The total and average daily out-patient visits for LRTI in Tianshui were 48,163 and 66,respectively.Female patients who visited the out-patient department for LRTI outnumbered male patients in these three cities.Out-patients aged 0-14 are significantly more than those aged 15-64 and≥65.2.Influence of different air temperature indexes on out-patient visits in three cities in Gansu Province:（1）Influence of mean temperature.There was a non-linear relation and hysteresis effect between daily mean air temperature and the out-patient visits in these three cities.The relation between the air temperature in Jiuquan and Dingxi and the number of residents’daily out-patient visits for LRTI were in an irregular“M”shape,and the relation between the air temperature in Tianshui and the number of out-patient visits for LRTI was in an irregular“L”shape.When the air temperature in Jiuquan fell within the range of-22～-10℃and 11～20℃,the effect of air temperature on the out-patient visits for LRTI was harmful.When the air temperature reached-22℃,the risk of out-patient visits in Jiuquan was the highest（RR=1.813,95%CI:1.209～3.005）.When the air temperature in Dingxi fell within the range of 8～16℃,the effect of air temperature on the out-patient visits for LRTI was harmful.When the air temperature was 14℃,the corresponding RR value reached the maximum（RR=1.348,95%CI:1.205～1.507）.When the air temperature in Tianshui fell within the range of 0～11℃,the effect of air temperature on the out-patient visits for LRTI was harmful.（2）Influence of DTR.There was a J-shaped non-linear relation between the DTR and the number of out-patient visits for LRTI in these three cities.Relatively high DTR was the main factor that causes an increase in residents’risk of out-patient visits for LRTI in these cities.The range of DTR that influences the number of out-patient visits for LRTI in Jiuquan was 21～24℃.RR value reached the maximum of 7.033（95%CI:3.770～13.119）at 23℃.The range of DTR that most significantly influences the number of out-patient visits for LRTI in Dingxi was 21～24℃.RR value reached the maximum of 2.057（95%CI:1.480～2.858）at 24℃.The range of DTR that most significantly influences the number of out-patient visits for LRTI in Tianshui was 20～24℃.RR value reached the maximum of 1.879（95%CI:1.379～2.561）at 24℃.（3）Influence of AT.There was an irregular M-shaped relation between the AT and daily out-patient visits of residents for LRTI in these three cities.When the AT was8～17℃in Jiuquan,the risk of out-patient visits for LRTI increased.RR value reached the maximum of 1.371（95%CI:1.088～1.728）.When the AT was-1～6℃in Tianshui,the risk of out-patient visits for LRTI increased.When the AT was,the RR value reached the maximum of 1.525（95%CI:1.071～2.171）with an AT of 0℃.However,the influence of AT on the number of out-patient visits of residents for LRTI in Dingxi was insignificant.3.Influence of different gender on out-patient visits in three cities in Gansu Province:（1）Influence of mean temperature.The influence of the daily mean air temperature on the out-patient visits in different gender groups in these cities in Gansu Province was inconsistent.In Jiuquan,the influence of low temperature on the number of out-patient visits for LRTI of female patients was greater than that of male patients,and the cumulative effect of low temperature on female patients increased with the extension of lag time.In Dingxi,the low temperature had a certain protective effect on both male and female patients in the late lag period.In Tianshui,the hysteresis effect characteristics of the influence of low temperature on the number of out-patient visits for LRTI in different gender groups were basically the same.The low temperature was more harmful to male patients than to female patients.In terms of high temperature,its influence on the number of out-patient visits for LRTI of female patients was greater than that of male patients in Jiuquan and Dingxi.In Tianshui,the effect of high temperature on male and female out-patient visits for LRTI was protective.（2）Influence of DTR.In terms of DTR,the influence of high DTR on the out-patient visits of female patients for LRTI was greater than that of male patients in these three cities.The harmful effect of high DTR on female patients had a lag effect.The time when the corresponding harmful effect occurred was Lag9d,Lag11d,and Lag9d,respectively.The cumulative effect of high DTR on female patients in these three cities was the greatest on Lag0-21d.The corresponding RR value was 1.641（95%CI:1.144～2.355）,1.342（95%CI:1.068～1.687）and 1.537（95%CI:1.234～1.914）.（3）Influence of AT.There were differences in the influence of AT on the out-patient visits in different gender groups in these three cities in Gansu Province.The influence of low AT on the out-patient visits in different gender groups in Jiuquan first increased and then decreased.Low AT had a certain protective effect on male and female patients in Dingxi.The harmful effect of low AT on female was greater than that on male.The influence of high AT on female patients who visited the out-patient department for LRTI in Jiuquan was greater,indicating that female is sensitive population.In Dingxi and Tianshui,the effect of high AT on male and female out-patient visits for LRTI was protective to some extent.4.Influence of different air temperature indexes on out-patient visits for LRTI in three cities in Gansu Province at different ages:（1）Influence of mean temperature.In terms of daily mean air temperature,in Jiuquan,the influence of low temperature on 0-14-year-old children and the elderly（≥65）was greater than that on adults（15-64）.In Dingxi,only an increase in the risk of out-patient visits of 0-14-year-old children for LRTI caused by low temperature was observed.The low temperature effect had a lag effect,and the harmful effect occurred on Lag17d.In Tianshui,the low temperature had a significant effect on the out-patient visits of adults（15-64）and 0-14-year-old children for LRTI.The effect on the out-patient visits of the elderly（≥65）for LRTI was protective in the whole lag period.The high temperature had a harmful effect on the number of out-patient visits of adults（15-64）and 0-14-year-old children for LRTI in Jiuquan at the early stage of lag.With the decrease in lag days,the harmful effect on the elderly（≥65）in Jiuquan occurred on Lag13d.In Dingxi,the influence of high temperature on the elderly was greater than that on adults（15-64）and 0-14-year-old children.In Tianshui,only an increase in the risk of out-patient visits of the elderly for LRTI due to high temperature was observed.（2）Influence of DTR.The influence of high DTR on the out-patient visits of 0-14-year-old children in Jiuquan and Dingxi was the most significant.In Tianshui,the influence of high DTR on the elderly（≥65）was great,while the effect on 0-14-year-old children and adults（15-64）was a protective effect.（3）Influence of AT.In terms of AT,the harmful effect of low AT on the elderly（≥65）in these three cities was significant,while the effect of low AT on adults（15-64）and 0-14-year-old children in Jiuquan and Dingxi was a protective effect on some lag days or in the whole lag period.The harmful effect of high AT on 0-14-year-old children in Jiuquan was significant.In Dingxi and Tianshui,the effect of high AT on the elderly（≥65）was great at the early stage of the lag and weakened with the extension of retardation time.The effect of high AT on 0-14-year-old children in Dingxi and Tianshui was a protective effect on some lag days or in the whole lag period.5.Influence of air temperature indexes in different seasons on out-patient visits in three cities in Gansu Province:（1）Influence of mean temperature.There were differences in the influence of the daily mean air temperature on the out-patient visits of residents for LRTI in these three cities in different seasons.In Jiuquan,low temperatures in winter and spring may increase the risk of out-patient visits of residents for LRTI.The influence of low temperature occurred on Lag9d and Lag4d,respectively,and then kept increasing.In summer,the high temperature had a harmful effect on the number of out-patient visits for LRTI.In Autumn,the air temperature within the range of-8～-4℃or 11～23℃had a harmful effect.In Dingxi,it was also observed that low temperatures in winter and spring may cause a significant increase in the risk of out-patient visits of residents for LRTI.When the air temperature fell within 1～3℃or 18～19℃in spring,it had a harmful effect on the out-patient visits of residents for LRTI.When the air temperature fell within-8～-6℃in winter,the risk of out-patient visits of residents for LRTI increased.When the air temperature fell within 15～17℃in summer and 9～13℃in autumn,the out-patient visits of residents for LRTI increased accordingly.In Tianshui,the high temperature in summer and low temperature in winter caused a significant increase in the risk of out-patient visits of residents for LRTI.When the air temperature fell within 16～21℃in summer and-4～3℃and 6～7℃in winter,harmful effects will emerge.When the air temperature fell within 9～15℃in spring and 5～10℃and 15～22℃in autumn,there will be a harmful effect.（2）Influence of DTR.In different seasons,the increase in DTR could cause an increase in the risk of out-patient visits of residents for LRTI.In Jiuquan,when the DTR was 7～19℃in spring and 4～12℃,and 17～21℃in summer,it had a harmful effect on the out-patient visits of residents for LRTI.The harmful effect of the DTR in summer was relatively weak.When the DTR in winter reached 12℃,a harmful effect was observed during Lag6d～Lag21d.In Dingxi,when the DTR in summer increased,the risk of out-patient visits for LRTI increased significantly.When DTR was 20℃,the RR value reached the maximum,1.176（95%CI:1.076～1.285）.When the DTR was 2～9℃and 11～23℃in spring,10～16℃in autumn,and 16～20℃in winter,a harmful effect was observed.The harmful effect of the DTR in Tianshui in spring and autumn was similar.As the DTR raised,the lag time also extended,and the harmful effect gradually increased.When the DTR was 2～5℃and 15～16℃in summer,the risk of out-patient visits for LRTI increased.The harmful effect of high DTR was greater.The DTR in winter had a relatively weak harmful effect.（3）Influence of AT.There were differences in the influence of AT on the out-patient visits of residents for LRTI in the three cities in different seasons.In Jiuquan,when the AT fell within 22～23℃in summer,-13～2℃and 16～20℃in autumn,and-18～-13℃in winter,the risk of out-patient visits of residents for LRTI increased.In Dingxi,the high AT in summer and the low AT in winter had harmful effects.When the AT fell within 12～20℃in summer,and-11～-5℃in winter,the risk of out-patient visits of residents for LRTI increased.In Tianshui,when the AT fell within 4～11℃and22～24℃in spring,25～26℃in summer,7～11℃in autumn,and-13～-4℃in winter,the risk of out-patient visits of residents for LRTI increased.Conclusions（1）Both low temperature and high temperature are the risk factors for the increase in the risk of out-patient visits for LRTI.In Jiuquan and Tianshui,the harmful effect of low temperature is greater and lasts longer,while the harmful effect of high temperature is greater than that of low temperature in Dingxi.0-14-year-old children and the elderly（≥65）are susceptible to low temperatures,while the harmful effect of high temperatures on female is greater than that on male.The harmful effects on the elderly are greater than that on 0-14-year-old children and adults.In the seasonal stratified analysis,the risk of out-patient visits for LRTI is the highest in winter and spring,while the low temperature in summer and high temperature in autumn also have certain harmful effects.（2）The exposure-response relation curve between DTR and the risk of out-patient visits for LRTI is J-shaped.The relatively high DTR is the main risk factor for the increase in the risk of out-patient visits for LRTI.The harmful effect of DTR has a certain lag effect.The greater the DTR,the earlier the harmful effect occurs,and the effect gradually increases with the extension of the lag time.The harmful effect of high DTR on female is greater than that on male.0-14-year-old children and the elderly are also susceptible to high DTR.In different seasons,the increase in DTR may cause an increased risk of out-patient visits for LRTI.There are greater harmful effects in spring and winter.（3）The exposure-response relation curve between AT and the risk of out-patient visits for LRTI is nearly M-shaped.The harmful effect of AT differs greatly in different cities.High AT in Jiuquan and Dingxi has a greater harmful effect,while low AT in Tianshui has a greater harmful effect.Compared with other groups,AT has a greater effect on female and the elderly（≥65）.The results of the seasonal stratified analysis showed that both high AT in summer and low AT in winter have certain harmful effects. |
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