Influence of air pollutants on pneumonia hospitalizations among children in a town in the Brazilian Legal Amazon region: a time series study

ABSTRACT BACKGROUND: Exposure to particulate material produced as a result of increased agricultural activity may increase the number of pneumonia hospitalizations among children. We hope to contribute to the knowledge base through highlighting the environmental mechanisms involved in this outcome and optimizing pollutant control policies. OBJECTIVES: To investigate the association between pneumonia hospitalizations among children and presence of environmental pollutants in a town in the Brazilian Legal Amazon region. DESIGN AND SETTING: Time series study conducted in the town of Tangará da Serra, Mato Grosso (MT), Brazil. METHODS: A total of 158 children aged 0 to 10 years participated in the study. Data on environmental variables and pollutants were extracted daily through the Coupled Chemistry-Aerosol-Tracer Transport model coupled to Brazilian Regional Atmospheric Modeling System (CCATT-BRAMS). Meteorological data were provided by the Weather Forecasting and Climate Studies Center (CPTEC). RESULTS: There was greater frequency of pneumonia hospitalizations in the months of transition between the rainy and dry seasons, with a prevalence ratio 2.4 times higher than in other periods. For environmental pollutants, there was a significant positive correlation between particulate matter (PM2.5) and pneumonia hospitalizations (correlation 0.11), with more admissions on the days when PM2.5 levels were highest (averages of 6.6 µg/m3 when there were no admissions and 13.11 µg/m3 on days with two or more admissions). CONCLUSIONS: The higher the PM2.5 level was, the greater the frequency of hospitalizations also was. Children living in peripheral areas had higher prevalence of pneumonia hospitalizations in the dry period than those who were living in the town center.


INTRODUCTION
Air pollution is gaining increasing importance within the environmental scenario because it causes great risks to health, with higher risk of death and respiratory diseases among children. 1,2 In 2016, one out of every nine deaths among children was attributed to the effects of pollution, with a total of 7 million deaths worldwide. 3 Particulate matter (PM) is a mixture of solid and liquid components formed by a variety of compounds that depend on the emission source. These fine and ultra-fine particles can reach the alveoli, where they are phagocytized by macrophages and neutrophils that release inflammatory mediators and may cause irritation to the eyes, throat and lungs. According to the World Health Organization (WHO), the mean limit of acceptability of exposure for particulate matter of size smaller than 2.5 μm (PM 2.5 ) is a concentration of 25 μg/m 3 for 24 hours. 4 Several mechanisms are involved in the respiratory disease caused by particulate matter, especially induction of pulmonary oxidative stress. This leads to overproduction of oxidative reaction, thus damaging the deoxyribonucleic acid (DNA) and inducing inflammatory lesions and epigenetic disorders, thereby contributing to the development of diseases such pneumonia. 5,6,7,8 Carbon monoxide (CO) is a systemic asphyxiant that induces depression of the central nervous system that at acute levels can cause death because it has affinity for hemoglobin that is 200 times higher than that of oxygen. In situations of chronic poisoning, slow hypoxia may develop and this may lead to permanent sequelae. 9  of 40,000 mg/m 3 (35 ppm) over a one-hour period that is not to be exceeded more than once a year. 10

OBJECTIVE
The objective of this study was to investigate the influence of pollutants on pneumonia hospitalizations among children in a town in the Brazilian Legal Amazon region. for pneumonia and CO and PM 2.5 levels and the independent variables were the climate variables.

METHODS
Associations were assessed between variables that correlated with the cases of hospitalization due to pneumonia, on the day of hospitalization. We separated the daily hospitalizations into three categories: days without hospitalizations, days with one hospitalization and days with two or more hospitalizations. To these, we applied the Kruskal-Wallis test and one-way analysis of variance (ANOVA).
The chi-square test was used to evaluate the number of daily hospitalizations per seasonal period (drought, transition and rain).
For all analyses, the significance level was set at P = 0.05, and the Epi-Info 6.04 and SPSS version 20.0 software was used. and five years old ( Table 1).

RESULTS
Regarding the distribution of cases in the city, it was observed that most were concentrated on the periphery, especially in neighbor-  Table 2.
Analysis on the behavior of pollutants between different seasonal periods showed that CO levels were higher during the rainy season, despite maintaining an average of 0.1 ppm, although there was a significant negative correlation with humidity. PM 2.5 levels were higher in the dry season, with an average of 10.7 μg/m 3 .
Among the climate variables (Table 3), temperature (T) was higher in the rainy season with an average of 25 °C. Relative humidity (RH) was higher in the rainy season (80.9%). Wind speed was higher in the rain season and transition period, with a speed of 2.1 m/s in both of these periods. Radiation was greater in the dry season, with an average of 765.6 kJ/m 2 .
After multiple linear regression, it was found that PM 2.5 level, RH and period of the year were predictors for pneumonia hospitalization among these children, as shown in Table 4.

DISCUSSION
There was a higher number of pneumonia hospitalizations among children aged 0 to 5 years, with predominance among males.
This had previously been seen in other studies, which reported that this difference between males and females was due to anatomical reasons. This was ascribed, for example, to immunological immaturity and reduced airway caliber, along with greater exposure to risk factors among boys at this age. 4,11,12 The findings showed that there was a significant positive cor- In our study, it appears that pollution caused by agricultural activity is higher than pollution resulting from vehicle traffic, since business activity in Tangará da Serra is essentially agricultural and its car fleet is not large, which also explains the low rates of CO emission in the study period.
There are some differences in the literature regarding relative air humidity. In a study by Kim et al., 4 it was found that there were differences among the geographical regions studied. There was a positive correlation in some regions but a negative one in others, which the authors attributed to local environmental factors. Ho  Table 4. Predictors for pneumonia hospitalization among children that were found to be statistically significant through multiple linear regression CO (carbon monoxide): adjustment variable. PM 2.5 = particulate matter; RH = relative air humidity.  30 In a study conducted in Turkey, there was harm to the respiratory tract after use of pesticides in agriculture. 31 Importantly, the effects of PM 2.5 on human health depend on its composition. In a systematic review in which the aim was to identify the properties of PM in the Amazon biome, its predominant characteristic was found to be high concentrations of biogenic elements during the rainy season and anthropogenic elements during the dry season. 32 In another study in Tangará da Serra, there was predominance of anthropogenic emissions over biogenic emissions. 33 These findings, which correlated with higher prevalence of pneumonia among children living in peripheral areas, may indicate that agricultural activities were having an influence.
In the transition months, there was greater wind speed, which may have dispersed the emissions produced by agricultural activities that were closer to the outskirts of the town, which may explain the increase in hospitalizations.
Policies for controlling pollutant emissions are paramount for reducing the damage to the health of vulnerable populations.
This was highlighted in a systematic review that was carried out to ascertain whether proximity to pollutants in the environment could cause adverse health outcomes. It was shown that populations living close to environmental risks seemed to be more likely to have adverse health outcomes, although this did not necessarily mean exposure at the individual level. 34 The limitations of the present study included its use of secondary data to obtain the environmental variables with the CCATT-BRAMS system, even though this is recognized to be a reliable mathematical model for estimates on emissions, along with its use of CPTEC data. In addition, the subjects were recruited through convenience sampling at the only public hospital in the town.
The sample was only of small size.

CONCLUSIONS
The higher the levels of PM2.5 were, the greater the frequency of hospitalizations also was. Children living in peripheral areas showed higher prevalence of pneumonia hospitalization during the dry season than did those who were living in the town center. Controlling and monitoring of air pollutant emissions, along with recognition of the type of particulate matter emitted in each region, can significantly help reduce unfavorable outcomes.
In particular, this is enabled through recognition of anthropogenic influences and implementation of measures for mitigation of the impact of agricultural activities.