Sex, Age, and Regional Disparities in the Burden of Asthma in Mexico from 1990 to 2019: A Secondary Analysis of the Global Burden of Disease Study 2019

Abstract

Asthma is the most prevalent cause of chronic respiratory diseases. Herein, we evaluate the asthma burden in Mexico based on results from the Global Burden of Disease (GBD 2019) study 2019. Using data from the GBD 2019, we estimated asthma prevalence, incidence, mortality, and disability-adjusted lived years (DALYs) counts and crude and age-standardized rates per 100,000 people with a 95% uncertainty interval (UI) by sex and age at the national and subnational levels in Mexico from 1990 to 2019. At the national level, asthma affected 3.35 million (95% UI, 2.59–4.37) people, with 606.0 thousand (433.0–811.1) new incident cases and 1655 (3–1931) deaths during 2019. Asthma caused a slightly higher burden in females and affected mainly age groups between 1 and 14 years of age. The burden of asthma gradually decreased from 1990 to 2010. However, during the last decade (2010–2019), prevalence increased by 8.2%, as did incidence, by 11.3%, whereas mortality and DALYs decreased by 23.3 and 1.6%, respectively. Finally, the burden of asthma displayed a heterogeneous pattern of disease at the subnational level. In conclusion, asthma causes a significant health loss in Mexico that differentially affects the population distributed among the states of the country, thus causing health disparities that should be addressed to provide sustainable asthma diagnosis and control to reduce its burden, especially in the early stages of life.

1. Introduction

Globally, asthma is one of the most common chronic respiratory diseases affecting people of all ages [1]. Clinically, asthma is defined as chronic inflammation of the airways characterized by bronchial hyperresponsiveness to a wide variety of stimuli, such as pollen, cat hair, and household dust. Episodic asthma attacks result in reversible airway obstruction causing symptoms such as coughing, recurrent wheezing, shortness of breath and chest tightness, among others [2,3]. Asthma has no cure, but good management with inhaled medications, mainly bronchodilators and steroids, in conjunction with a reduction in exposure to asthma-triggering stimuli is needed to reduce inflammation and control the disease [4], thus allowing asthmatic people to live a normal life [5]. Nevertheless, asthma management and control in people living in low-income countries have been reported to be inadequate [6].

According to recent results from the Global Burden of Disease study 2019 (GBD 2019), the global prevalence of asthma was estimated at 3.54%, affecting 264.2 million people and causing 37 million new incident cases, with 461 thousand deaths worldwide in the general population during 2019 [7]. These figures explain why asthma represents a significant global economic burden and a worrying public health problem, which needs attention to develop prevention and cost-effective management approaches in middle- and low-income countries [2]. Therefore, there is an ongoing international and cooperative effort focused on describing the burden of asthma, as well as its control and management in different settings and locations in the world [8,9,10,11,12]. In Mexico, although several studies and surveys have been conducted on the epidemiology of asthma [13,14,15,16,17], these are limited to some locations, age groups, and years covered. In addition, given that Latin American countries are characterized by enormous contrasts in social, cultural, genetic, and environmental conditions both between and within localities, a heterogeneous epidemiology of asthma within a country is expected [18]. Thus, there is a need to estimate and describe the national and subnational burden of disease caused by asthma in Mexico.

In the present study, we conducted a secondary analysis using updated and reliable data from the most recent iteration of the GBD 2019 study [19]. Our analysis assessed the burden of disease caused by asthma in the general population of Mexico and by sex and age group from 1990 to 2019 at the national and subnational levels. The results from this study will be helpful in identifying the trends of asthma and finding any existing health disparities caused by this chronic respiratory disease. Likewise, describing the subnational pattern will be useful to guide location-specific efforts aimed at alleviating health loss due to asthma in places where the burden is the highest. Given that asthma is considered a public health issue, knowing its epidemiology represents an opportunity to respond to a growing problem by providing sustainable health management that incorporates efficient diagnosis and control measures in the most vulnerable population affected by this disease.

2. Methods

2.1. Overview of the Global Burden of Disease Study

The GBD 2019 study represents the most comprehensive global effort to understand the 369 leading causes of disease and injury affecting the population [19], including the study of the risk factors associated with health loss in men and women of all age groups in 204 countries and regions [20]. The present study was conducted in compliance with the GBD protocol by members of the GBD Mexico collaborative network [21,22]. Our study presents a secondary analysis of the estimates produced by the GBD in the last iteration of 2019 at the Institute for Health Metrics and Evaluation (IHME), which is an independent institute at the University of Washington. Accordingly, our study used the estimations publicly available from the Global Health Data Exchange (GHDx) database of the IHME. The estimates produced by the GBD complied with the Guidelines for Accurate and Transparent Health Estimates Reporting (GATHER) statement [23].

2.2. Case Definition

According to the 10th revision of the International Statistical Classification of Diseases and Related Health Problems (ICD–10) of the World Health Organization (WHO), asthma corresponds to code J45 (J45.0, 45.1, 45.8, and 45.9). According to the GBD 2019, asthma is defined as a chronic lung disease characterized by bronchial spasms usually caused by allergic or hypersensitivity reactions that make breathing difficult. The case definition includes wheezing in the past year and self-report of a medical diagnosis (GBD 2019 two-pagers Asthma Level 3, pp. 24–25) [19].

2.3. Data Sources for the Modeling and Data Collection Process

In 2019, the GBD used 2891 data sources to estimate the fatal (2478) and nonfatal (413) components of the global burden of asthma, which are available for consultation at the following link: https://ghdx.healthdata.org/gbd-2019/data-input-sources (accessed on 12 April 2023). The GBD relies on secondary data and data collected by health ministries, a vast network of scientists, medical professionals, and government officials, all of whom participate in the creation of the most accurate disease and mortality estimates in the world. The primary data collection process consists of the following six steps: research design, project planning, instrument development, training and pilot, data collection, and analysis. The details are described in the Protocol for the Global Burden of Diseases, Injuries, and Risk Factors available at https://www.healthdata.org/sites/default/files/files/Projects/GBD/March2020_GBD%20Protocol_v4.pdf (accessed on 1 August 2023).

In the case of asthma, the GBD relied primarily on data collected by other research organizations, and these data are gathered mainly by the GBD collaborator network that is formed by >7000 persons across the globe. This is because local stakeholders and in-country partners have the necessary expertise to localize specific data for a given country. Data sources included: (1) representative censuses, household surveys, and epidemiological surveillance data at the population level (national and subnational), from which data were captured on the use, access to, expenditure on, and perceived quality of treatment for the disease; (2) vital record systems and verbal autopsies, from which information was collected regarding the signs, symptoms, and demographic characteristics of the population with a disease, or questionaries are used to determine the individual’s cause of death by obtaining information from someone familiar with the deceased; (3) scientific articles focused on describing prevalence, systematic reviews and meta-analyses, and epidemiological surveillance data; and 4) information on medical claims and visits to health services. For the case of Mexico, 46 data sources were used and are listed in Supplementary Table S1.

2.4. Estimation of the Fatal Component

For the fatal component that includes deaths and years of life lost (YLLs), the GBD used the cause of death assembly model (CODEm), which is a standard and optimized GBD tool that is based on an assembly of different modeling methods. CODEm incorporates covariates that produce estimations of high predictive validity (pages 258–260, Appendix 1 of the GBD 2019 study) [19]. The flowchart and codes needed for the estimation of the fatal component of asthma can be found at the following link: https://ghdx.healthdata.org/gbd-2019/code/cod-2 (accessed on 15 March 2023). Briefly, the process includes (1) standardization of the data sources, (2) mapping according to the ICD, (3) sex and age split, (4) redistribution of the junk codes, (5) noise reduction, and (6) generation of the database. From the database, covariates are entered (i.e., cumulative cigarette consumption for 10 and 5 years, healthcare access and quality index, outdoor pollution by fuels and PM2.5, per capita income, education, and the sociodemographic index) and models are produced to estimate (1) the number of deaths due to asthma by locality/year/age/sex and (2) the number of YLLs, which represent the sum of years of life lost due to premature death multiplied by the standard life expectancy for a locality [24].

2.5. Estimation of the Nonfatal Component

The link https://ghdx.healthdata.org/gbd-2019/code/nonfatal-2 (accessed on 15 March 2023) presents both the flow chart and the codes used by the GBD to generate the nonfatal asthma estimates. Briefly, data processing was first performed, which consisted of (1) age and sex split, using the Meta-regression Bayesian Trimming tool (MR-BRT) to break down the estimates by sex proportionally to existing reports and fitting a cubic spline for age showing high values of asthma prevalence in younger males and a subsequent increase in older females; (2) modeling the excess mortality rate; and (3) adjusting for bias with MR-BRT, which allowed for improved comparability between different case definitions and study designs, as well as data from medical claims and surveillance studies (pages 883–887 of Appendix 1 of the GBD 2019 study) [19]. Then, from the processed data, a database was generated and used in the Disease Modeling Meta-Regression 2.1 (DisMod-MR 2.1) tool by which prevalence and incidence by locality/year/age/sex were estimated. The predictor covariates described below were also included during this process. Additionally, to estimate the number of years lived with disability (YLDs), prevalent cases were separated by severity into four patient groups using medical expenditure surveys: asymptomatic, controlled, partially controlled, and uncontrolled, and adjusted with the disability weight according to each severity level (Supplementary Table S2). YLDs represent the years of life lost due to disability caused by a disease and are obtained by multiplying the disability weight (0 = no health loss to 1 = death) caused by a specific sequela of the disease by the prevalence of that disease [24].

2.6. Predictive Covariates

The GBD used a collection of predictive covariates to model the fatal and nonfatal components of the asthma burden. The covariates, which were obtained from prior studies that found an association between them and asthma epidemiology, were incorporated into the DisMod model and divided into three levels (pages 258–260 and 883–887 of Appendix 1 of the GBD 2019 study) [19]. The first level included cumulative consumption of cigarettes (5 or 10 years) and standardized exposure variable (scalar combining exposure to all asthma risk factors) both of which showed a positive association with the estimations, and the healthcare access and quality index, which showed a negative influence; the second level, those which showed a positive influence on the direction of estimations and included smoking prevalence, indoor air pollution (such as cooking fuels), and outdoor air pollution measured as the concentration of PM_2.5; and the third level, those that were negatively associated with the estimates and included 10-year income per capita, education attainment (years per capita), and sociodemographic index (SDI, that integrates three dimensions (fertility, education, and lag-distributed income per capita)). The average standardized betas from each covariate indicated, for instance, that positive coefficients for the cumulative consumption of cigarettes, outdoor pollution, and indoor pollution were positively associated with increased death due to asthma. By contrast, negative coefficients for SDI, income per capita, healthcare access and quality, and years of education were associated with decreased death due to asthma [19].

2.7. Metrics and Reporting Standards

To estimate the burden of asthma in Mexico, we used publicly available data from the online query tool GHDx (https://vizhub.healthdata.org/gbd-results/ accessed on 6 January 2023). We collected the estimates at the national and subnational levels for the 32 states by sex and 5-year age groups for the period from 1990 to 2019 [25]. To summarize the burden of asthma, we used counts, as well as the crude and age-standardized rate per 100,000 people for prevalence, incidence, mortality, and disability-adjusted life years (DALYs). DALYs incorporate both the fatal and nonfatal burden of asthma and correspond to the sum of YLLs and YLDs. All estimations were made by locality, year, sex, and age group, with 95% uncertainty intervals (UIs). For the estimates, uncertainty was propagated through each modeling step for 1000 draws, with UIs representing the 25th and 975th percentiles of the ordered 1000-draw distribution [7]. In addition, we assessed trends in the asthma burden using annual estimates for the 30-year time series and estimated the crude, age-standardized percent change for each measurement over the last decade (2010 to 2019). The GBD 2019 study used Python version 3.7.0 (Python Software Foundation), Stata version 15.1 (StataCorp), and R version 3.4.1 (R Foundation). We used Prism 10 (GraphPad Inc., USA) to create all graphs.

3. Results

3.1. Temporal Changes in the Burden of Asthma in Mexico from 1990 to 2019

In general, changes in the crude estimates of the burden of asthma in Mexico were observed throughout the period studied. Although there was a trend toward a reduction in the number of cases from 1990 to 2000, during the decade from 2010 to 2019, there was an increase in the national burden of asthma. The percentage of deaths due to asthma increased by 1.56%, with prevalence and incidence showing the largest increase in the period (

Table 1. Estimated burden of asthma by decade and percentage change from 2010 to 2019 in the general population in Mexico.

Measure	Counts (95% UI)				Percentage Change from 2010 to 2019
	1990	2000	2010	2019
Prevalence	3,193,956 (2,488,868 to 4,169,496)	2,962,753 (2,357,733 to 3,736,388)	2,985,740 (2,326,062 to 3,862,882)	3,353,355 (2,591,663 to 4,377,729)	12.31 (7.51 to 17.35)
Incidence	617,319 (455,781 to 841,052)	548,240 (415,215 to 717,186)	551,725 (408,040 to 751,456)	606,000 (433,053 to 811,132)	9.84 (4.01 to 15.72)
Deaths	2871 (3 to 3052)	2137 (3 to 2272)	1630 (3 to 1795)	1655 (3 to 1931)	1.56 (−15.11 to 17.56)
DALYs	210,448 (160,471 to 281,254)	177,374 (132,575 to 241,540)	160,769 (115,591 to 228,457)	172,041 (120,406 to 249,530)	7.01 (1.04 to 12.96)

DALYs = disability-adjusted lived years, 95% UI = 95% uncertainty interval.

). A similar trend was observed in the age-standardized prevalence and incidence rate per 100,000 persons; despite the substantial reduction in the period from 1990 to 2010, there was an increase from 8.22 to 11.3%, respectively, between 2010 and 2019 (Figure 1a,b). By contrast, both mortality and DALY rates tended to decrease between 1990 and 2019, although, in both measurements, a differential slowdown in the reduction was observed during the last decade, as the age-standardized mortality rate per 100,000 persons decreased by 23.3% (95% uncertainty interval, 11.40 to 35.38%) from 2010 to 2019, and the DALY rate by 1.64% (8.40 to 5.24%) in the same period (Figure 1c,d).

3.2. Comparative Global, Regional, and National Burden of Asthma in 2019

Figure 2 depicts the comparative ranking of the age-standardized rates of prevalence, incidence, DALYs, and deaths due to asthma in 2019. The results showed a contrasting pattern at the global level, the five regions in which the GBD divides the American continent, and Mexico, which is located within the Central Latin America region, along with eight other countries. Supplementary Table S3 summarizes the estimates for each measure by location.

With 9848.1 (8624.3 to 11,312.1) and 6450.2 (5427.8 to 7800.4) prevalent cases per 100,000 people, high-income North America and Southern Latin America were the two top-ranked regions, while Central Latin America and Mexico occupied the lowest positions (3244.4 and 2765.1 prevalent cases, respectively). With respect to the age-standardized incidence, again, high-income North America (1474.1, 1188.9 to 1810.7) was the top-ranked, followed by the Caribbean (938.4 (741.7 to 1179.0) in second place, while Mexico and the global level were ranked at the bottom of the list, with 523.8 and 504.3 incident cases per 100,000 people in 2019. The age-standardized ranking for DALYs and mortality per 100,000 people due to asthma showed a distinct pattern because the Caribbean (422.8, 315.7 to 553.5 DALYs) and the global level (5.8, 4.6 to 7.0 deaths) occupied the top position for each measure, respectively. Mexico was ranked at the bottom position for DALYs and was ranked at the third highest position for the age-standardized rate of death.

3.3. Burden of Asthma in Mexico in 2019 by Sex

In Mexico, 3.35 million (2.59 to 4.37 million) prevalent cases of asthma were estimated in the general population in 2019 (Table 1), of which 50.48% corresponded to women (1.69 million, 1.33 to 2.16), with a higher age-standardized rate in males than in females (2767.1 vs. 2746.4 prevalent cases per 100,000 persons, respectively) (

Table 2. Estimated burden of asthma in Mexico in 2019.

Metric	Counts (95% UI)			Age-Standardized Rate per 100,000 (95% UI)
	Female	Male	Female Contribution (%)	Female	Male
Prevalence	1,692,794 (1,334,895 to 2,166,356)	1,660,561 (1,267,499 to 2,211,723)	50.48	2746.4 (2137.3 to 3560.5)	2767.1 (2106.6 to 3697.1)
Incidence	295,287 (216,132 to 390,011)	310,713 (216,900 to 428,426)	48.72	507.8 (367.0 to 676.8)	537.7 (375.1 to 745.6)
Deaths	903 (2 to 1,123)	753 (1 to 929)	54.52	1.4 (1.1 to 1.7)	1.2 (1.5 to 0.9)
DALYs	88,271 (62,589 to 126,512)	83,769 (58,016 to 122,582)	51.30	143.1 (100.9 to 206.9)	141.9 (98.6 to 206.9)

DALYs = disability-adjusted lived years, 95% UI = 95% uncertainty interval.

). Regarding the incidence of asthma, 606,000 new cases (433,053 to 811,132) occurred in 2019 in males and females of all ages (Table 1), with a lower proportion of incident cases in females (48.72% of total) and a higher age-standardized incidence rate in males (537.7, 375.1 to 745.6 per 100,000 people) (Table 2).

A total of 1655 (3 to 1931) people died from asthma in Mexico in 2019 (Table 1), with women being the sex most affected by the disease, as they contributed 54.52% of the total deaths, although with similar age-standardized rates of 1.4 and 1.2 deaths per 100,000 people for females and males, respectively (Table 2). In addition, in the general population, the count of DALYs due to asthma was estimated at 172,041 (120,406 to 249,530), with a slightly higher burden of the disease in women than in men judging by the 88,271 DALYs (62,589 to 126,512) estimated in women, which corresponded to 51.3% of the total, and a higher age-standardized rate in females that corresponded to 143.1 (100.9 to 206.9) DALYs per 100,000 people (Table 2).

3.4. Burden of Asthma in Mexico in 2019 by Age Group

The burden of asthma in Mexico varied according to age group and sex. The three youngest age groups (1–14 years) accounted for 51.18% of the total prevalent cases (Supplementary Table S4), with a higher contribution of cases in males than in females, a trend that was reversed for the remaining groups (Figure 3a). The prevalence rate per 100,000 people ranged from 1193 to 6687 cases, with the highest value in the pediatric population aged 5–9 years and with increasing values in adults aged 75 years and older (Figure 3a and Supplementary Table S5). Children under 14 years of age accounted for 73.04% of incident cases of asthma, with the peak of the distribution in infants aged 1–4 years (Supplementary Table S4) and a higher incidence in children for the first two age groups (Figure 3b. With a value of 2463 (1440 to 3895) cases per 100,000 people, the population aged 1–4 years had the highest asthma incidence rate, which steadily decreased as age increased, although there was a trend toward higher values after the age of 75 years (Figure 3b and Supplementary Table S5).

Mortality due to asthma showed a different pattern since the highest number of deaths was observed among adults older than 70 years, reaching its maximum value in persons aged 80–84 years (Supplementary Table S4). Women presented an equal or higher number of deaths than men in all age groups (Figure 3c). In the population younger than 50 years, the mortality rate per 100,000 people was close to zero but increased from age 75 years onward until reaching its peak of 104 deaths (75 to 127) in the >95 years age group (Figure 3c and Supplementary Table S5). Finally, the distribution of the number of DALYs and their rate per 100,000 people showed contrasting patterns between age groups (Figure 3d), as the population <14 years accumulated the highest DALY count (Supplementary Table S4), with a higher proportion in men. The highest rates of DALYs per 100,000 people were observed in persons >85 years (Figure 3d and Supplementary Table S5).

3.5. Asthma Burden and Trends at the Subnational Level

At the subnational level, there were contrasting patterns of asthma burden in men and women of all ages (Supplementary Table S6). Among the 32 states of Mexico, the crude prevalence ranged from 21,021 to 411,104 cases and from 3621 to 78,148 incident cases in 2019. Colima, Baja California Sur, Campeche, Nayarit, and Tlaxcala had the lowest values for both estimates, while Puebla, Jalisco, Veracruz, and Mexico were characterized by the highest prevalence and incidence of the disease. To exemplify the heterogeneity of the spatial distribution of the asthma burden, Figure 4a shows a map with the relative contribution of each state to the national total DALYs due to asthma in 2019. The map shows that the highest percentages of DALYs occurred in some entities distributed in the central belt (Jalisco, Guanajuato, Estado de Mexico City, Puebla, and Veracruz) and in the southern region of the country. However, other states, such as Colima, Morelos, and Tlaxcala, had low contributions of between 0.65 and 1.51% of the national total DALYs, even though these states are also located in the central belt of the country. Similar results were observed for the number of deaths in 2019 (Supplementary Table S6).

In addition to spatial heterogeneity, there were also temporal disparities in the changes in the crude estimates of the asthma burden from 2010 to 2019 among the 32 states of Mexico (Supplementary Table S7). First, crude prevalence and incidence cases tended to increase in all localities at the subnational level, with percentages varying between 2.58 and 40.23 for the former and 0.43 and 33.74 for the latter from 2010 to 2019. Second, the changes in the count of DALYs and asthma deaths presented a contrasting pattern because Baja California Sur, Quintana Roo, Queretaro, and Colima showed considerable increases of between 20 and 40% in the number of DALYs, whereas only Veracruz, Guerrero, and Tabasco showed a slight reduction during the period (Figure 4b). By contrast, 10 of the 32 states of the country showed a reduction in the number of deaths due to asthma during the same decade (Supplementary Table S7).

Finally, to comparatively analyze the change in the asthma burden between states and the national benchmark, the age-standardized rate (per 100,000 people) for the beginning and end of the period (1990 and 2019) was plotted for each state and compared against the national average. In Figure 4c, a high initial disparity is shown, with rates ranging from 386.9 to 180.19 DALYs per 100,000 people, which declined to comparable estimates (109.94 to 184.95) in 2019 in all states, among which nine were below the national average. Similar results are displayed in Figure 5, which summarizes the change in the age-standardized prevalence, incidence, and mortality rates per 100,000 people at the subnational level from 1990 to 2019. In general, there were high and heterogeneous estimates at the beginning of the period, which decreased across states by 2019. Only 6 states had standardized prevalence and incidence rates below the national average in 2019, while 15 states had an asthma mortality rate below the national benchmark. Mexico City, Nuevo Leon, and Estado de Mexico consistently ranked below the national average, while Quintana Roo and Veracruz were the two states with the highest values for all three measures.

4. Discussion

Our results indicate that asthma should be considered a public health problem because it affected 3.35 million people in Mexico in 2019. This value corresponds to a prevalence of 2.85% (2.2 to 3.72%) among the Mexican population, which despite being lower than the global prevalence of 3.53% (3.01 to 4.16) and the 3.34% (2.63 to 4.24) for Central Latin America where Mexico belongs [25], still represents a significant health loss in the country due to this chronic respiratory disease.

Across the American continent, asthma caused the highest burden in high-income North America and South America, as judged by the 10.31% and 7.06% total prevalent cases due to asthma for the populations of these regions. Comparatively speaking, the burden of disease attributed to asthma in Mexico was the lowest in contrast to the five regions across the American continent. Even though asthma is considered an urban-related disease in Latin American countries [18], our results indicate that low-income countries from the Caribbean, Andean, and Central Latin America regions had higher asthma prevalence estimations. Therefore, not only the urban environment but also poverty and lack of healthcare access might contribute to the higher burden of asthma in countries from the region. Similarly, the idea that the rural areas of Latin American countries are protected against asthma and thus have a lower prevalence contrast with our results, as judged by the higher values of asthma prevalence found across Latin America, which is characterized by a greater proportion of rural areas [26]. However, this discrepancy in the region could also be explained by rapid urbanization and migration from rural locations, which are demographic factors likely to be driving the asthma epidemic in the region [18].

Even though the age-standardized rates of prevalence, incidence, and DALYs per 100,000 people we found for Mexico were among the lowest in the Americas, the death rate due to asthma was ranked third highest, thus indicating greater mortality caused by the disease. Nevertheless, the age-standardized rate of death due to asthma in Mexico was 1.5 (1.2 to 1.8) per 100,000 people, which clearly contrasted with the rate found in the Caribbean (4.5, 3.4 to 5.8) and the global level (5.8, 4.6 to 7.0), which were ranked second and top, respectively. Indeed, the death rate found in Mexico was slightly above the estimates for Central, Tropical, and Southern Latin America, whose values ranged between 1.1 and 1.4 deaths per 100,000 people. Factors that could explain this regional disparity may be related to case definition differences between countries, the number and quality of data input sources used to model the burden, and the years covered for each country. However, further studies with in-depth analysis of the causes of these differences are warranted.

According to our results, the burden of asthma in Mexico showed a contrasting temporal pattern during the decade from 2010 to 2019. Regarding the crude counts, prevalence, incidence, DALYs, and deaths due to asthma showed an increase that varied between 1.56 and 12.31 for this period. By contrast, the age-standardized prevalence increased by 8.2%, as did the incidence, by 11.3%, whereas the mortality and DALY age-standardized rates decreased by 23.3 and 1.6%, respectively. These trends contrasted with the global estimations of asthma, which showed that while the number of patients with asthma increased globally, mainly due to population expansion, the age-standardized prevalence decreased [27]. Recently, there have been some unexpected changes in the prevalence of asthma, which has decreased in low-income countries but increased in middle-income countries, while it remains stable among high-income and upper-middle-income countries [28]. A simple explanation is that the underdiagnosis of asthma is common in low-income countries. Nevertheless, in the United States and some other high-income countries, there has been a rise in the number of asthmatic patients, which at least for the United States has been associated with public health campaigns to increase awareness and diagnosis of this respiratory disease, as well as overdiagnosis [29]. Additionally, it is possible that the reduction in DALYs and mortality due to asthma may be associated with an increase in awareness of the disease associated with the publication and updating of international guidelines, as well as the development and distribution of treatments for the control of the disease [30,31].

Although these arguments may help explain the trends reported herein for Mexico, it is important to consider some additional aspects that may also contribute to the increasing trend of asthma prevalence that we found. First, an elevated body mass index (BMI) has been associated with a higher burden of asthma [7]. Thus, the growing obesity epidemic that Mexico is experiencing may be linked to the rise in the number of asthmatic patients. Second, air pollution is produced because of urbanization and industrial emissions, both of which are considered major causes of respiratory diseases and asthma development [32]. Third, changes in temperature and the broader distribution and dispersal of allergens and infectious vectors are due to extreme weather events caused by climate change and global warming [33]. Fourth, endogenous and exogenous factors may influence the changing pattern of asthma, among which ethnicity [34], pulmonary microbiome [35], depression, anxiety, and emotional stress are the main endogenous factors, and differential exposure to microbes, pollens, smoke, and dust are considered among the exogenous factors [36]. Nevertheless, future studies are warranted to assess both the extent and magnitude to which these distinct factors are linked to the changing burden of asthma that we report.

Asthma remains a public health problem worldwide and varies broadly globally because, in adults, the prevalence ranges from 0.2 to 21.0% and from 2.8 to 37.6% in children between 6 and 7 years of age [37]. Other studies have shown differences in the prevalence of asthma among adolescents ranging from 0.9% in India to 21.3% in South Africa [38]. By contrast, the prevalence of childhood asthma in China appears to be very low (0.9 to 1.5%) [39]. Our results indicated a sex and age disparity in the burden of asthma because this respiratory disease differentially affected females and males according to age group. Asthma prevalence was higher in boys than in girls between the ages of 1 and 14 years. A similar result was observed in incidence, which exhibited higher values among boys from 1 to 9 years of age. Nonetheless, the values were inverted after puberty, with prevalence and incidence being higher in females than in males. These results concur with a well-documented sex bias in asthma prevalence [40,41] and the highest incidence of asthma occurring in childhood at an average age of 10 years [42].

Our results showed a great geographical disparity in the burden of asthma at the subnational level, which coincided with the complex burden of disease previously documented for other causes of health loss [21,43]. Even though the pattern of disease is expected to vary both between and within countries, the spatial differences documented herein may be partially explained by some of the following factors: First, the estimates that we used were produced by the GBD using a limited amount of data sources, which additionally were scarce for some locations and for some years. As a result, the limited number of data points may have introduced bias into the estimation and a lack of representativeness for some states. Second, the heterogeneous socioeconomic conditions and complex geography across the territory of Mexico that create differential conditions for developing asthma symptoms may contribute to the differences seen among states. Third, several social and lifestyle factors, such as diet, obesity, psychosocial stress, and mental illness, that have been recently investigated and associated with asthma are expected to vary broadly among the population and thus contribute to regional disparities [44]. Fourth, despite the existence of guidelines for the management of asthma in Mexico that have been adapted from high-quality guidelines [45,46,47], there have been barriers and limitations that prevent their effective implementation across the states of Mexico. For instance, the inaccessibility of some medicines, the opposition of healthcare personnel to accepting changes to new strategies and treatments, the costs of health management, and the accessibility and quality of public and private health services. Finally, given that Mexico lacks a national asthma strategy, which is fundamental to help reduce the local disparities reported in our study [48], awareness of this disease relies on local programs implemented to diagnose and control asthma. However, the lack of a common national plan to tackle this disease may contribute to fueling the differential burden of disease caused by asthma across the states of Mexico. Consequently, in our country, there is still a need to assess whether local asthma programs and accessibility to treatment, along with the changes in regional incomes and exposure to local changing environmental conditions, influence the regional disparities documented herein. Therefore, further subnational representative studies are needed in Mexico to assess the origin of the geographic differences documented in this study.

Although we found that Mexico had a lower prevalence of asthma in comparison to other regions of the American continent, the country possesses a large population of more than 130 million people; thus, small improvements in the management and outcomes for asthmatic people in the country may induce a relatively large impact on the total number of people affected by asthma. In this regard, Mexico relies on different guidelines for the management of asthma, such as the Mexican Asthma Guide 2017 [49], Comprehensive Asthma Management: Guidelines for Mexico 2021 [50], and Clinical Practice Guideline: Evidence and Recommendations—Treatment of Asthma in the Pediatric Age Group [51]. These guidelines are directed to the health sector and healthcare professionals with the purpose of diffusing information and aiding stakeholders in managing the selection and acquisition of medicines. Additionally, these guides are useful as sources of advice during diagnosis and treatment according to sex, age, and severity of the disease considering the special needs of pregnant women and elderly individuals, and to recommend adjustments in comorbidities such as obesity, anxiety, and depression disorders, among others. However, the reduced availability of scientific publications and reports on the epidemiology of asthma nationally and subrationally in Mexico prevents an understanding of both the magnitude of this disease and the impact of any action taken to reduce its burden. Therefore, our results may provide a useful point of reference in further assessments of the effect of national or local strategies against asthma.

Mexico lacks a national asthma action plan, which is fundamental to achieving a large reduction in the global and national burden of this respiratory disease [48]. Consequently, there is an urgent need for the implementation of a national strategy against asthma by focusing on early detection, providing access to effective anti-inflammatory treatment, and refining the medication strategy to improve adherence and reach an optimal pharmacological treatment, avoiding the underuse of medicines that could lead to unwanted side effects and possible exacerbations of the symptoms [52,53]. In addition, an effective national asthma strategy should consider government commitment, proper registration of outcome data, asthma management guidelines, and education of the public to increase awareness [48]. Without an adequate diagnosis and control of the disease, there will be a continuous growth in uncontrolled asthma that will result in excessive health loss and economic burden [54], especially among the most vulnerable population, thus increasing the gap between people due to lack of access to healthcare. Additional steps should be taken toward reducing the health burden due to asthma in Mexico, for instance, reducing the cost of medication, ensuring its wide distribution and availability, implementing local campaigns in the most affected areas, generating more specialized healthcare providers, establishing asthma clinics across the states, encouraging adherence to treatment, and conducting censuses in schools to determine the effect of asthma on the student population. Consequently, providing more sustainable health management for asthma control should help reduce the preventable burden caused by this disease and concomitantly increase the quality of life of patients as well as reduce the cost associated with uncontrolled asthma.

5. Limitations

Our study has several limitations. First, the reduced number of data input sources used to model the burden of asthma in Mexico created a high level of uncertainty that accompanied the estimates for several locations and years covered. The high heterogeneity documented here mainly arises due to the scarcity of input sources for some states and years, thus introducing bias and affecting the accuracy of the estimates. Consequently, some of the estimates should be taken with caution due to their high amount of uncertainty. Second, although we used the most recent iteration of the GBD data, these estimates may be considered dated and could have changed during recent years in part because of the factors previously described as well as COVID-19. Therefore, this study should be further updated with more recent data. Third, we did not perform a risk factor analysis to understand their specific contribution to the national and subnational burden of asthma in Mexico. The GBD includes metabolic (BMI), behavioral (smoking), and environmental (occupational asthmagens) risks, which are known for their broad variation across the populations of different regions and nations and could have been used to help explain the subnational heterogeneity. Fourth, there is a lack of an association analysis between the asthma burden and socioeconomic data at the subnational level. The GBD produces the SDI, and it is used as a comparative descriptor of socioeconomic development both between and within countries. Given that asthma burden and income have been positively associated, the inclusion of this analysis could be useful to explain regional disparities.

6. Conclusions

In Mexico, asthma represents a public health problem that has shown an increasing trend in its incidence and prevalence. The burden of this disease differentially affects males and females of distinct age groups, with the highest incidence, prevalence, and DALYs in the early stages of life, and the highest mortality due to asthma among the older population. These results and the existence of geographic disparities highlight the need for both a national strategy and a subnational asthma control plan to reduce preventable health loss and reduce the gap between the affected populations from each state. In addition, raising awareness regarding the appropriate diagnosis and control management by care providers will benefit patients by improving their quality of life. The high heterogeneity found for several locations and years justifies the need to produce more nationally representative studies as well as subnational surveys for Mexico. Adding these data to the GBD modeling process may help to reduce the uncertainty and thus generate more robust and consistent estimates based on a larger number of data sources and with greater coverage at the subnational level, differentiating the presentation of data by sex and age group.