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Abstract
Introduction Heatwave is a major global health concern. Many countries including China suffered a record-breaking heatwave during the summer of 2022, which may have a significant effect on population health or health information-seeking behaviours but is yet to be examined.
Methods We derived health information-seeking data from the Baidu search engine (similar to Google search engine). The data included city-specific daily search queries (also referred to Baidu Search Index) for heat-sensitive diseases from 2021 to 2022, including heatstroke, hospital visits, cardiovascular diseases and diabetes, respiratory diseases, mental health and urological diseases. For each city, the record-breaking heatwave days in 2022 were matched to days in the same calendar month in 2021.
Results The 2022 record-breaking heatwave hit most cities (83.64%) in Mainland China. The average heatwave duration was 13 days and the maximum temperature was 3.60°C higher than that in 2021 (p<0.05). We observed increased population behaviours of seeking information on respiratory diseases (RR=1.014, 95% CI: 1.008 to 1.020), urological diseases (RR=1.011, 95% CI: 1.006 to 1.016) and heatstroke (RR=1.026, 95% CI: 1.016 to 1.036) associated with the heatwave intensity in 2022 (per 1°C increase). The heatwave duration in 2022 (per 1 day increase) was also associated with an increase in seeking information on cardiovascular diseases and diabetes (RR=1.003, 95% CI: 1.002 to 1.004), urological diseases (RR=1.005, 95% CI: 1.002 to 1.008), mental health (RR=1.009, 95% CI: 1.006 to 1.012) and heatstroke (RR=1.038, 95% CI: 1.032 to 1.043). However, there were substantial geographical variations in the effect of the 2022 heatwave intensity and duration on health information-seeking behaviours.
Conclusion This infodemiology study suggests that the 2022 summer unprecedented heatwave in Mainland China has significantly increased population demand for health-related information, especially for heatstroke, urological diseases and mental health. Population-based research of real-time disease data is urgently needed to estimate the negative health impact of the exceptional heatwave in Mainland China and elsewhere.
- public health
- geographic information systems
- epidemiology
Data availability statement
Data are available in a public, open access repository. Baidu Search Index records can be obtained from the official Baidu index website (https://index.baidu.com/). Daily ambient temperature and dew temperature data covering the same study period can be obtained from the ERA5-Land dataset (https://cds.climate.copernicus.eu/). Population data can be obtained from the WorldPop dataset (https://hub.worldpop.org/). The daily ambient mean concentration of PM2.5 and O3 can be obtained from the Tracking Air Pollution in China (TAP, http://tapdata.org.cn).
This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.
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WHAT IS ALREADY KNOWN ON THIS TOPIC
Heatwave is a planetary health threat and an exceptional heatwave in the summer of 2022 has affected many countries including China in the northern hemisphere.
There have been no studies looking at the potential impact of the record-breaking 2022 heatwave on population health or population health information-seeking behaviours in Mainland China, largely due to the time lag in the collection of real health or disease data such as hospital-based morbidity and mortality.
WHAT THIS STUDY ADDS
This study showed that an increase in heatwave intensity and duration of the unprecedented 2022 heatwave could boost health information-seeking behaviours for heatstroke and urological diseases.
Higher intensity (not duration) of the 2022 heatwave increased the health information-seeking behaviours for respiratory diseases; longer duration (not intensity) of the heatwave increased health information-seeking behaviours for cardiovascular diseases and diabetes and mental health.
There were appreciable geographical differences in the effect of the 2022 exceptional heatwave on information-seeking behaviours.
HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY
The unprecedented exceptional 2022 heatwave in Mainland China has significantly increased population health information-seeking behaviours involving multiple health-related outcomes, most likely suggesting a broad-range health effect and a great disease burden resulting from the 2022 heatwave.
In the context of global warming, future heatwave events will undoubtedly occur more frequently and last longer, making it an urgent need to use real-time health data or infodemiology study to assess the impact of the 2022 heatwave and similar exceptional heatwaves on population health in China and other affected countries in the northern hemisphere.
Introduction
Heatwave is a major public health threat globally and nationally.1 2 In the 21st century, exceptional heatwaves have occurred in many countries such as the 2003 heatwave in France, the 2010 heatwave in India and the 2011 heatwave in Australia.3–5 In 2022, a record-breaking and large-scale heatwave in the northern hemisphere affected areas and populations on an unprecedented scale. For example, in China, the National Climate Centre confirmed that the heatwave in 2022 reached the strongest level since 1961.6
Existing studies worldwide have found that heatwaves can increase morbidity and mortality from a wide range of diseases such as cardiovascular diseases, respiratory diseases and urological diseases. Researchers also found that health risk such as morbidity or mortality could be differently affected by heatwave intensity and duration.7 As one of the countries hit by the 2022 record-breaking heatwave, the effect of this heatwave on the health of Chinese people needs to be assessed. However, there has been no evidence of the health effect of the 2022 heatwave in Mainland China. One underlying reason may be the lag in collecting health data considering the complex data collection and verification process.8 To address the problem of lagging health data collection, researchers have sought to employ other alternative epidemiological methods, one of which is infodemiology that makes full use of real-time web-based big data when real-time disease data are not available.9 Studies in the USA and China have shown that the volume of internet searches correlates well with a real-time reflection of disease.10–12 The internet is a predominant channel for people to obtain information about health issues nowadays.13 The available online search data are a voluntary expression of public concerns and needs,12 and patients who come from countries such as the USA with high internet penetration are increasingly using the internet to search for health information before and after medical consultations. In addition to being a remedy for the lag in health data collection, internet search data have unique advantages in assessing the health impact of heatwaves. For example, some people with mild symptoms or who are susceptible but not yet sick also tend to search the internet for solutions,12 but such health status is difficult to be investigated when studying the health impact of heatwaves in comparison to traditional hospital-based morbidity or mortality data.14 Another example is mental health which can easily involve respondents' privacy, leading to a low response rate in epidemiological surveys or information bias due to the fabrication of facts.15 16 Internet searches are usually anonymous and spontaneous and reflect well the true wishes of the person concerned.17
To date, online search data have been extensively used in the field of public health worldwide. For instance, Google Trends in the USA has been successfully used in investigating population health such as mapping population depression,11 monitoring the prevalence of burns,18 tracking cases of e-cigarette-related lung injury19 and analysing the impacts of COVID-19.20 21 Similar to the Google Trends, the Baidu Search Index (BSI) is calculated by the Baidu search engine based on the search volume of internet users in Baidu.22 In China searches on Baidu accounted for 90.90% of web search engine users.23 BSI has been already used in studies investigating Chinese health-related information-seeking behaviours such as the early warning and monitoring of COVID-19 and attention to urological diseases.12 24 According to the latest Statistical Report on Internet Development in China, as of June 2022, the number of internet users in China was approximately 1.1 billion and the internet penetration rate reached 74.40%,25 together with the 2022 exceptional heatwave, providing a good chance to conduct infodemiology study on heatwave and population health.
We carried out an infodemiology study in Mainland China with the aim to examine the relationship between the record-breaking heatwave in 2022 and population health information-seeking behaviours. Specifically, this study has two major objectives: (1) to quantitatively describe the 2022 record-breaking heatwave and the population health information-seeking behaviours nationally and regionally; (2) to unravel how the 2022 record-breaking heatwave including its intensity and duration has affected the population health information-seeking behaviours.
Methods
Infodemiology data collection
In this infodemiology study in Mainland China, city-specific daily data on population behaviours of seeking health-related information during the summer period (June–August) of 2021 and 2022 were obtained by using an array of keywords in the official website of the BSI (https://index.baidu.com). By consulting with clinicians and reviewing the literature on high temperature and population health, the selected keywords were widely reported high temperature-related health outcomes involving six aspects including hospital visits, respiratory diseases, cardiovascular diseases and diabetes, urological diseases, mental health and heatstroke. We used the keywords in Chinese including the full name and the abbreviation of each disease or common negative behaviour to obtain relevant BSI. The included keywords of BSI are shown in online supplemental table S1.
Supplemental material
Daily ambient maximum temperature and average relative humidity data for each city were derived and calculated from ERA5-Land dataset that provided hourly weather data with a spatial resolution of 0.1°×0.1° (approximately 10 km × 10 km).26 27 Daily air pollutant data as potential confounders were collected from the Tracking Air Pollution in China (TAP) dataset, including hourly concentrations of PM2.5 and O3, with a spatial resolution of 1 km × 1 km (approximately 0.01°×0.01°).28–31 TAP is a multiscale, near real-time dataset of Chinese atmospheric aerosol and gaseous pollutant concentrations constructed by fusing ground-based observations, satellite remote sensing, emission inventories and other multisource data.32 Population data of China in 2020 with a spatial resolution of 1 km × 1 km were sourced from Population Counts of WorldPop.33 To facilitate the subsequent data analysis, the spatial resolution of all data was adjusted to 0.1°×0.1° by using raster package of R language. All required data spanned from 2021 to 2022, except for the temperature data that ranged from 2011 to 2022.34
Identification of the exceptional heatwave event in 2022
An exceptional heatwave event is mainly characterised by extremely high temperature that lasts for many more days than usual. However, there is no universal definition of exceptional heatwave events globally and regionally. First, we considered a widely used heatwave definition that is applicable to Chinese populations.34 35 A common heatwave is defined as a period of at least two or more days in which the daily maximum temperature exceeded the 92.5th percentile of daily maximum temperature distribution during the reference period (2011–2022). This definition is based on a national study associating heatwave with 259 million deaths in China.36 However, for a city there are two or more heatwave events according to this definition in 2022 that could be separated by non-heatwave days, making it hard to determine the minimum number of days for defining the exceptional heatwave event. To capture the long-lasting record-breaking heatwave in 2022, we considered the delayed health effect of the heatwave that is widely reported to persist for about 7 days.37 38 Therefore, we chose 7 days as the minimum duration for the definition of the exceptional heatwave event in 2022 allowing for the observation of the maximum lagged effect of heatwaves on health information-seeking behaviours. If there were two or more heatwave events in a city in 2022, we only chose the heatwave that lasted for 7 or more days as well as had the highest average daily maximum temperature during the heatwave event so as to focus on the exceptional heatwave in terms of duration and intensity. The average daily maximum temperature within a heatwave period was used to capture the heatwave intensity. This definition for the 2022 exceptional heatwave is also generally in agreement with the relevant releases from the National Climate Centre in terms of affected regions and heatwave characteristics (ie, duration and intensity).6
Statistical analysis
Similar to a case-crossover study, we matched days of the exceptional heatwave event in 2022 to control days in 2021 that were not the exceptional heatwave event to construct matched multicity data.39 40 As such, the control period in 2021 also included common heatwave rather than the exceptional heatwave. Additionally, compared with the prepandemic of COVID-19, the COVID-19 pandemic in China saw a sudden and significant increase in people’s reliance on interest use, including the frequency of using and time spent on the internet.41 Therefore, choosing the control period before the pandemic cannot rule out the influence of the pandemic. Conversely, choosing a control period close in time can greatly reduce the effect of time-varying confounding factors on the results. Finally, we chose the summer of 2021 as the control period. This methodology examined contrasts within matched strata, thus eliminating potential confounding effect caused by factors that remain relatively stable within a year such as the level of the economy, population and the green space.42 Since an exceptional heatwave event can also occur during the control period in the same city in 2021, following the methodology of previous similar studies,43 44 an adjustment was made to ensure that the control period did not contain exceptional heatwave events. Specifically, for each heatwave day of the exceptional heatwave event in the control period, we replaced their data using the average of the summer (from June to August) days during the period other than exceptional heatwave events in the same city in 2021 (online supplemental figure S1).
Considering the spatial variation in population size, we used the BSI per 100 000 people related to population health information-seeking behaviours (bsi) as the dependent variable in the later data analysis.24 The effect of the heatwave was evaluated in terms of both heatwave intensity and duration. To assess the effect of the intensity of the 2022 heatwave on population health information-seeking behaviours, daily population-weighted maximum temperatures (pwt) was calculated by using the formula as follows45:
(1)
rmaxtem and rpop are daily maximum temperature and population data at a resolution of 0.1°×0.1°, respectively. nj is the total number of square blocks within city j.
In order to consider the effect of the spatial distribution of the independent variable on the dependent variable nationally, a panel spatial error regression model (PSEM) using cities as individual fixed effect based on the least squares dummy variable (LSDV) is constructed, which is shown as follows46:
(2)
In the equation, v is the number of independent variables, k is the variable identifier, β is the regression coefficient, fixed is the variable fixed by the LSDV method and ζ is the residuals of PSEM. λ is the spatial autoregressive coefficient of PSEM. The spatial weight matrix is denoted by W and generated based on the spatial location relationships.46 For controlling the multicollinearity among the independent variables, the principal component analysis was embedded in PSEM.47 48 First, the original five independent variables including average daily population-weighted maximum temperature, duration, average daily relative humidity, average daily PM2.5 and average daily O3 during exceptional heatwave events in 2022 and control period in 2021 were transformed into the five principal component variables (pc1…pc5). Then, the principal component variables were used for constructing the regression model. Finally, the modelled relationship between the principal component variables and the dependent variables was transformed back into that of the original variables and the dependent variables. The ultimate PSEM of this study is shown as follows:
(3)
In the equation, city represents a city with an exceptional heatwave event in 2022. In addition to the intensity and duration of the heatwave, other exposure elements act as covariates to control for potential confounding effect. The relative risk (RR) is calculated by the following equation:
(4)
where βres indicates the regression coefficient of the original variable. To explore regional differences in the effect of the 2022 heatwave on health information-seeking behaviours, we repeated the above-mentioned data analysis for six geographical areas including northeast, south-central, east, north, northwest and southwest.1
A series of sensitivity analyses were also carried out to verify the stability of the regression results. A panel linear regression model using the same data with PSEM (Model 1) was fitted to judge whether PSEM was superior based on the second-order Akaike’s Information Criterion. In addition, considering that the selection of the control period was somewhat arbitrary, we also used an alternative approach in data analysis by excluding cities that experienced any heatwave events during the 2021 control period (Model 2). We used R software (V.4.2.1; R Foundation for Statistical Computing, Vienna, Austria) to conduct all the analyses.
Patient and public involvement
Patients and the public were not involved in the design, conduct, reporting or dissemination plans of our infodemiology study.
Results
Characteristics of 2022 summer record-breaking heatwave
In the 2022 summer period, 83.64% (225/269) of Chinese cities suffered exceptional heatwave events. These cities made up the final study area and are located in six geographical regions (Hong Kong, Macau and Taiwan were not included due to the lack of BSI data) (online supplemental figure S2).1 The median value of the population-weighted maximum temperature during the exceptional heatwave period in 2022 was 33.44°C and 29.84°C for the control period in 2021, respectively (figure 1C). The spatial distribution of population-weighted maximum temperature during the exceptional heatwave period in 2022 was characterised by relatively higher temperature in the northwest, the south-central and the east and relatively lower temperature in the southwest, the north and the northeast (figure 1B). The exceptional heatwave events in 2022 lasting more than 2 weeks occurred in over 140 cities and its spatial distribution was characterised by longer duration in the east, the south-central, the southwest and the northwest, and shorter duration in the north and the Northeast (figure 2).
Spatial and temporal distribution of the average daily population-weighted maximum temperature during the 2022 exceptional heatwave period and matched control period in 2021. Comparisons between subgroups were conducted using Wilcoxon signed-rank test. *p value <0.05.
Spatial and temporal distribution of the duration of the 2022 exceptional heatwave events.
Characteristics of health information-seeking behaviors
During the study period, there were approximately 3.5 million records (BSI) pertaining to population behaviours of seeking information on hospital visits, respiratory diseases, cardiovascular diseases and diabetes, urological diseases, mental health and heatstroke across Mainland China. The proportion of BSI of cardiovascular diseases and diabetes reached 38.23% during the exceptional heatwave period in 2022, which was much larger than the BSI of mental health (18.88%), heatstroke (15.40%), respiratory diseases (12.90%), urological diseases (10.34%) and hospital visits (4.25%) (online supplemental figure S3). Compared with the control period (non-exceptional heatwave days) in 2021, the median value of BSI of heatstroke in 2022 record-breaking heatwave period increased by 180.77%, which was much larger than the median value of BSI of cardiovascular diseases and diabetes (18.94%), hospital visits (13.00%), mental health (11.98%), urological diseases (11.25%) and respiratory diseases (1.10%) (figure 3).
Comparison of BSI for different health outcomes in 2021 and 2022. BSI/100 000 stands for the BSI per 100 000 people. Comparisons between subgroups were conducted using Wilcoxon signed-rank test. *p value <0.05. BSI, Baidu Search Index.
Associations between the 2022 summer record-breaking heatwave and health information-seeking behaviours
At the national level, except for BSIs for hospital visits, the BSIs for other health outcomes were affected by the 2022 heatwave, with homogeneity and heterogeneity in the effect of the intensity (per 1°C increase) and duration (per 1 day increase). Specifically, both the intensity and duration of the 2022 heatwave increased the BSI of heatstroke and urological diseases and had the greatest effect on the BSI of heatstroke (figure 4). Furthermore, we observed that higher intensity (not duration) of the 2022 heatwave increased the BIS of respiratory diseases (RR=1.014, 95% CI:1.008 to 1.020); longer duration (not intensity) of the heatwave increased BSI of mental health (RR=1.009, 95% CI:1.006 to 1.012) and cardiovascular diseases and diabetes (RR=1.003, 95% CI:1.002 to 1.004) (figure 4).
Effect of the 2022 heatwave on Baidu Search Index for different health outcomes. (A) The effect of intensity of the 2022 heatwave. (B) The effect of duration of the 2022 heatwave. Intensity is the averaged daily population-weighted maximum temperature during the 2022 exceptional heatwave period. RR, relative risk.
Across six geographical regions, we also observed differences in the effect of the 2022 heatwave on BSIs of health outcomes. Regarding the effect of the higher intensity of the 2022 heatwave, there were four regions with significant increases in BSI for heatstroke (south-central, northwest, north, east), three regions with significant increases in BSI for cardiovascular diseases and diabetes (southwest, northeast, east) and four regions with the significant increase in BSI for urological diseases (southwest, south-central, north, east) (online supplemental figure S4). Regarding the effect of the longer duration of the 2022 heatwave, BSI for heatstroke increased significantly in all regions; BSI for mental health increased significantly in all regions except for south-central; other BSIs showed significant increases in at least three regions except for hospital visits. Furthermore, the effect of the 2022 heatwave on BSI of cardiovascular diseases and diabetes was the largest in the Northeast (online supplemental figure S5).
In the sensitivity analyses of using different control periods and different model specifications, effect estimates were generally consistent with those from the PSEM. Specifically, the PSEM could better fit the relationship of BSI with the 2022 heatwave (intensity and duration) than Model 1 for all health outcomes (online supplemental table S2); the effect of the heatwave duration on BSI was more consistent when using different control selections and model specifications than the heatwave intensity; the effect of the heatwave intensity was higher when compared with control period without any heatwave days (online supplemental figure S6).
Discussion
Our study leveraged online search engine data and reported for the first time the health-related effect of the 2022 record-breaking heatwave in Mainland China. We observed that the 2022 heatwave was associated with increased online information-seeking behaviours for heatstroke, cardiovascular diseases and diabetes, respiratory diseases, urological diseases and mental health. This study also found appreciable differences in the effect of the 2022 heatwave on information-seeking behaviours for different health outcomes and across different regions.
At the national level, the increased intensity of the 2022 heatwave was associated with an increase in health information-seeking behaviours about all health outcomes except for hospital visits. Noticeably, the 2022 heatwave had the largest effect on health information-seeking behaviours for heatstroke compared with other health information-seeking behaviours. It is now widely accepted that heatstroke during heatwaves is usually caused by exposure to high temperature (the intensity of the heatwave).49 We additionally observed in this study that the higher intensity and longer duration of the heatwave could also significantly increase the health information-seeking behaviours of heatstroke. However, because of the lacking of heatstroke epidemiology data for a large spatial area in China,50 current national studies about the significant effect of heatwave duration on heatstroke have not been found. Only a few regional studies, for example, Li and colleagues in Chongqing, China showed that the prolonged duration of heatwaves can increase the incidence of heatstroke.38 Therefore, the increased duration of the 2022 heatwave may be a risk factor for heatstroke but yet to be ascertained. Besides, heatstroke is also thought to play a major role in causing urological diseases because it is accompanied by an elevated core temperature, dehydration and blood hypertonicity.51 To date, urological diseases have caused a considerable burden of disease: for example, over 750 million people have kidney diseases and the loss of disability-adjusted life years reached 36 million in 2017.52 Similar to the effect of the 2022 heatwave on seeking behaviours for heatstroke, the increases in both the intensity and duration of the 2022 heatwave could increase seeking behaviours for urological diseases. In the context of global warming, future heatwave events will undoubtedly occur more frequently and last longer,34 making it a high priority to pay more attention to exceptional heatwave-sensitive diseases such as heatstroke and urological diseases.
This study found that population health information-seeking behaviours associated with cardiovascular and respiratory diseases accounted for more than half of the total searches during the 2022 heatwave period (online supplemental figure S3). Between 1990 and 2017, the top three causes of death in China were stroke, ischaemic heart disease and chronic obstructive pulmonary disease, all of which were in the category of cardiovascular or respiratory diseases and may be affected by the 2022 heatwave.53 For example, a worldwide meta-analysis and systematic review by Cheng and colleagues showed that exceptional heatwaves in many countries increased mortality and morbidity from cardiovascular and respiratory diseases.54 Our study also found that an increase in the intensity or duration of the 2022 heatwave could increase health information-seeking behaviours for cardiovascular and respiratory diseases. However, the 2022 heatwave had different effects on seeking behaviours of cardiovascular and respiratory diseases in terms of duration and intensity. Specifically, the higher 2022 heatwave intensity only significantly increased seeking behaviours for respiratory diseases and did not significantly increase seeking behaviours for cardiovascular diseases and diabetes. In contrast, an increase in the duration of the 2022 heatwave could increase the seeking behaviours for cardiovascular diseases and diabetes but not respiratory diseases. However, current studies are inclined to support that higher heatwave intensity and longer heatwave duration can increase morbidity or mortality from cardiovascular and respiratory diseases.36 54–56 The differences between the results of our study and those of previous studies may be associated with the fact that our study was based on health information-seeking behaviours rather than real health outcomes. In addition, the increased intensity and duration of the 2022 heatwave could increase searches for cardiovascular diseases and diabetes, and respiratory diseases in some regions, but not others (online supplemental figures S4 and S5). Such spatial variation when aggregated at a larger geographical area could lead to the non-significant effect of national intensity or duration of the 2022 heatwave on specific diseases.
Interestingly, the 2022 heatwave was significantly associated with increased health information-seeking behaviours for mental health in Baidu search engine, with longer duration boosting the seeking behaviours and higher intensity discouraging the seeking behaviours. Similarly, using Google Trends in Google search engine, Wang et al found that higher temperature did not lead to an increase in searches of depression in the USA.11 Furthermore, one recent study from Vietnam reported that extended heatwave duration rather than increased intensity increased the risk of hospitalisation for mental diseases.57 One possible reason for the contrasting effect of heatwave intensity and duration is that people could stay indoors to promptly avoid exposure to high temperature during the heatwave days, but the long-lasting heatwave period likely force people to stay indoors for weeks, which tends to generate negative emotions and increases the stress to mental health.58
At the regional level in Mainland China, the effect of the 2022 heatwave on population health information-seeking behaviours also varied greatly across regions. The regional differences may be associated with latitude because people in high latitude are reported more susceptible to the health hazards of heatwaves.36 For example, the 2022 heatwave had the greatest effect on health information-seeking behaviours for cardiovascular diseases and diabetes in the northeast. Similarly, these regional differences may also be associated with the economic level: the lower the economy, the more susceptible the population is to the health hazards of heatwaves.59 For example, the duration of the 2022 heatwave in the northwest had a higher effect on all health information-seeking behaviours in this study than those in the east. Additionally, the economic level of the northwest is known to be lower than that of the East. Besides, the level of green space cover and other factors across regions may also influence the effect of the heatwaves.60
Our study still has limitations. First, data from Baidu search engine was used in this study, while other search engines such as Sogou and 360 Search were not used. Nevertheless, Baidu was used by the largest number of internet users in Mainland China, which to some extent represent population health information-seeking behaviours. Second, we used the BSI data aggregated at the city level, which hindered us from conducting finer spatial analysis and cannot identify the within-city variation in the effect of the 2022 heatwave. Third, the BSI data do not have city-level personal information such as age and gender, and therefore cannot analyse the effect of the 2022 heatwave on the information-seeking behaviours among different groups of people. Fourth, our control period was chosen only in 2021, and although its comparability was good, it may generate some random errors. Therefore, we also checked the information released by the National Climate Centre, and no large-scale extreme temperature events were reported in Mainland China in the summer of 2021.
Nevertheless, this study used the infodemiology technology, which has the unique advantage of timely and fast identification of the potential health effects of heatwaves and other weather extremes. Therefore, this study suggests that infodemiology in countries or regions with a high internet penetration rate can be served as an important supplement to the traditional environmental study of weather extremes (eg, 2022 exceptional heatwave) and human health, aiming to provide early and first-hand evidence-based information for the heatwave-related health early warning when the real-time health data are not available.
Conclusion
This infodemiology study provides novel evidence that the 2022 summer unprecedented heatwave in Mainland China has significantly increased population behaviours of seeking health-related information on cardiovascular diseases and diabetes, heatstroke, urological diseases, mental health, and respiratory diseases. Therefore, population-based research of real-time disease data is urgently needed to assess the negative health impact of the 2022 exceptional heatwave in China and elsewhere.
Data availability statement
Data are available in a public, open access repository. Baidu Search Index records can be obtained from the official Baidu index website (https://index.baidu.com/). Daily ambient temperature and dew temperature data covering the same study period can be obtained from the ERA5-Land dataset (https://cds.climate.copernicus.eu/). Population data can be obtained from the WorldPop dataset (https://hub.worldpop.org/). The daily ambient mean concentration of PM2.5 and O3 can be obtained from the Tracking Air Pollution in China (TAP, http://tapdata.org.cn).
Ethics statements
Patient consent for publication
References
Supplementary materials
Supplementary Data
This web only file has been produced by the BMJ Publishing Group from an electronic file supplied by the author(s) and has not been edited for content.
Footnotes
ZL, YF and HS are joint first authors.
Handling editor Seye Abimbola
CH and JC contributed equally.
Contributors JC and CH conceived and designed the study. ZL, YF and HS analysed the data. ZX and HCH conducted the literature review. HZ and JT were involved in data collection and curation. YZ, MZH and KH provided strategic guidance and oversight. ZL, YF and HS drafted the manuscript with feedback from all authors. JC and CH verified the raw data. HZ, QZ and JT verified the results of this study. All authors had full access to all the data in the study. All authors contributed to data interpretation, read and approved the final manuscript and had final responsibility for the decision to submit for publication. JC is responsible for the overall content as the guarantor. The guarantor accepts full responsibility for the work and/or the conduct of the study, had access to the data, and controlled the decision to publish.
Funding This study is supported by the National Natural Science Foundation of China (Grant No. 42105165), the High-level Scientific Research Foundation of Anhui Medical University (Grant No. 0305044201) and the Discipline Construction of Anhui Medical University (Grant No. 0301001836).
Competing interests None declared.
Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting or dissemination plans of this research.
Provenance and peer review Not commissioned; externally peer reviewed.
Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.