Abstract
Objective. To evaluate exposure to environmental factors inhaled during pregnancy and after birth until juvenile idiopathic arthritis (JIA) diagnosis among residents of a large city.
Methods. This is an exploratory case-control study that consists of 66 patients with JIA and 124 healthy controls matched by age and sex, living in the São Paulo, Brazil, metropolitan area until JIA diagnosis, and whose mothers had resided in this region during pregnancy. A structured and reliable questionnaire (κ index for test-retest was 0.80) assessed demographic data, gestational and perinatal-related factors, and exposure to inhalable environmental elements during pregnancy and after birth (occupational exposure to inhalable particles and/or volatile vapor, exposure to cigarette smoke, and the presence of industrial activities or gas stations near the home, work, daycare, or school). Tropospheric pollutants included particulate matter (PM10), sulfur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3), and carbon monoxide (CO).
Results. During pregnancy, intrauterine cigarette smoke exposure (OR 3.43, 95% CI 1.45–8.12, p = 0.005) and maternal occupational exposure (OR 13.69, 95% CI 4.4–42.3, p < 0.001) were significant independent risk factors for JIA diagnosis. In contrast, maternal employment (OR 0.06, 95% CI 0.02–0.2, p < 0.001) and ideal maternal weight gain (OR 0.36, 95% CI 0.2–0.8, p = 0.017) presented negative associations. Secondhand smoke exposure from birth to JIA diagnosis (OR 3.6, 95% CI 1.8–7.3, p < 0.001) and exposure to O3 during the second year of life (OR 2.76, 95% CI 1.20–6.37, p = 0.017) were independent and significant risk factors for the pathogenesis of JIA.
Conclusion. In our study, cigarette smoke exposure (intrauterine and after birth), exposure to O3 in the second year of life, and maternal occupational exposure were identified as potential risk factors for JIA, warranting further study.
Exposure to fine/ultrafine particles and other pollutants has been associated with disturbances in systemic inflammation and immune responses1,2,3,4. Ambient (outdoor) and household (indoor) pollutants are both important environmental risks to human health5. Indoor pollutants include cigarette smoke, domestic dust, and volatile organic compounds6,7. The outdoor pollutants monitored by environmental agencies are sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), ozone (O3), and particulate matter (PM10)5.
Fine and ultrafine inhalable particles are those with diameters smaller than 2.5 µm and 0.1 µm, respectively. These particles consist of solid and liquid parts, in which several compounds are adsorbed. Exposure to these inhalable particles can trigger pulmonary oxidative stress and inflammation8, and may lead to systemic inflammation. Exposure to air pollutants may increase inflammatory cytokines levels in adults and children, such as interleukin 1β, interleukin 6 and tumor necrosis factor-α9,10. However, few studies have evaluated an association between exposure to outdoor pollutants and rheumatic diseases in adults2,3,11,12,13,14 or children4,15,16,17,18,19.
Prenatal exposure to environmental factors has been associated with several childhood diseases. In fact, fetal exposure to toxins has been linked to early programming for childhood illnesses17,20,21. However, studies on pediatric rheumatic diseases involving exposure to inhalable pollutants during pregnancy, and from birth to disease diagnosis, are still rare16,17,18,19,22,23,24.
Juvenile idiopathic arthritis (JIA) is a heterogeneous group of autoimmune diseases and it is the main cause of chronic arthritis in children and adolescents25. Some studies have associated environmental factors with JIA onset or diagnosis16,18,22,23,24. However, to our knowledge, the simultaneous evaluation of exposure to outdoor and indoor pollutants during pregnancy and from birth to JIA diagnosis has not yet been performed. The aim of our study was to analyze exposure to inhaled environmental factors both during pregnancy, and from birth to JIA diagnosis.
MATERIALS AND METHODS
This is an exploratory case-control study. From January 2013 to December 2014, the Pediatric Rheumatology Unit of the Children’s Institute, Faculdade de Medicina da Universidade de São Paulo, Brazil, followed up on 172 patients with JIA classified according to the International League Against Rheumatism (ILAR) criteria25. Of these patients with JIA, 66 fulfilled the inclusion criteria for our study: they were residents of the São Paulo metropolitan area up to JIA diagnosis whose mothers had resided in this region at least 1 year before pregnancy, as well as during pregnancy. Patients with other pediatric chronic diseases and with incomplete information regarding pregnancy were excluded.
The control group was composed of 124 healthy age- and sex-matched children and adolescents who did not have any chronic inflammatory diseases. They were recruited from the primary care clinic after routine checkups, and fulfilled the same inclusion criteria as patients with JIA. Socioeconomic status was classified by the Brazilian Association of Market Research Institutions26. The Ethics Committee of our University Hospital approved our study (registration number 0095/09), and written informed consent was signed by the parent or guardian of the child. If age-appropriate, consent was obtained from the participating child.
Structured questionnaire to assess inhaled environmental factors
The data were obtained from patients with JIA and healthy control mothers by means of a structured questionnaire. A questionnaire that had been previously used by Guimarães, et al27 and Orione, et al17 was modified to include the following variables: (1) sociodemographic characteristics (socioeconomic status was classified by the Brazilian Association of Market Research Institutions26 and took into account the educational level of the head of the family and the family’s purchasing power); (2) JIA and control mothers’ addresses during pregnancy (all addresses were evaluated, including relocations); (3) JIA and control mothers’ occupations during pregnancy, including mother’s occupation, commute time from home to workplace, and occupational exposure to specific pollutants, such as inhalable particulate matter (demolition, school chalk, sewing, construction, and quarry dust) and/or volatile vapor (paints, varnish, gasoline vapor, and other volatile substances); (4) gestational and perinatal-related factors, such as weight gain during pregnancy, gestational age, birth weight, and alcohol consumption during pregnancy28; (5) presence of stationary environmental sources (gas stations, factories, and quarries) within a radius of up to 500 meters from the residence, workplace, daycare, or school during JIA and control pregnancies, from birth to JIA diagnosis in the JIA group, and from birth to mean age at JIA diagnosis (6 yrs) in the control group; and (6) smoking by household residents during pregnancy and after birth for a 6-year period. In most cases, the period between birth and JIA diagnosis was 6 years. Therefore, a 6-year period was adopted to explore exposure after birth.
From April to June 2014, a pilot study was performed involving 21 consecutive mothers. The subjects were also retested 5 to 10 days after the first questionnaire to ensure their understanding of the questions and to assess applicability and reliability of the questionnaire. Of note, these 21 mothers were included in the final analysis. After 5 to 10 months, a new evaluation with the same questions as in the test-retest was performed to verify the consistency of the answers over a longer interval.
Tropospheric pollutants and weather data
The São Paulo State Environmental Agency (CETESB)29 provided daily concentrations of PM10 (24-h average), SO2 (24-h average), NO2 (the highest hourly average), O3 (the highest hourly average), and CO (the highest 8-h moving average) from 22 automated pollution-monitoring stations in different parts of the São Paulo metropolitan area. The average pollutant levels measured at each station were adopted as an exposure status throughout the city because air pollutant levels recorded in each station were highly correlated.
The average concentration of each pollutant was calculated throughout the gestational period and from birth to JIA diagnosis in the JIA group, and from birth to the mean age of JIA diagnosis (6 yrs) in the control group. No patient with JIA and healthy control had the same birth date.
Statistical analysis
Continuous variables [mean ± SD or median (IQR)] and categorical variables (%) for patients with JIA and healthy control groups were included in descriptive analyses. Data were compared by Student t tests or Mann-Whitney U tests for continuous variables. Categorical variables were assessed by chi-square test or Fisher’s exact test. The test-retest reliability of the questionnaire was verified using the κ index.
According to the characteristics of exposure assessed by the questionnaire, 7 groups of independent variables were defined (similar to Orione, et al17):
Employment. Maternal employment and occupational exposure to either of the following inhalable agents (dichotomous): inhalable particulate matter and/or volatile vapor.
Daycare/school attendance, from birth until JIA diagnosis (dichotomous).
Exposure to cigarette smoke. Exposure to cigarette smoke during pregnancy was evaluated using these dichotomous variables: maternal smoking; maternal secondhand smoke exposure (mother who did not smoke but was exposed to secondhand smoke); and intrauterine cigarette smoke exposure (smoking mother and/or mother exposed to secondhand smoke). After birth, exposure to cigarette smoke was evaluated using 2 dichotomous variables: secondhand smoke exposure (child or adolescent exposed to secondhand smoke after birth); and child or adolescent always exposed (intrauterine and secondhand smoke exposure after birth).
Gestational and perinatal-related factors, such as weight gain during pregnancy (< 11.5 kg, 11.5–16 kg; > 16 kg)32, prematurity, birth weight (< 2.5 kg; 2.5–4.0 kg; > 4.0 kg), and alcohol consumption during pregnancy30 (yes or no, dichotomous).
Home, workplace, daycare, or school distance to stationary environmental sources of inhalable pollutants (< 100, 100–200, and 200–500 m) during pregnancy, and from birth to JIA diagnosis.
Exposure to traffic based on commute time from home to work, or to daycare or school (< 30, 30–60, and > 60 min), and 5 indicators of exposure to tropospheric pollutants in each pregnancy trimester and in each year from birth until JIA diagnosis.
Seasonality: season in late pregnancy (categorized).
Average concentration of each tropospheric pollutant in pregnancy (first, second, and third trimesters) and for each year from birth to JIA diagnosis were categorized into tertiles for each participant.
Variables with levels < 20% significance in a univariate model were used in multilevel models. We adopted a multilevel logistic regression model based on 7 groups of independent variables to identify variables for the final multiple model.
Independent variables that presented a significance level < 5% were used in the final multiple model. Regression model results were presented as OR and 95% CI. In all the statistical tests, significance was set at 5% (p < 0.05). The IBM-SPSS-20 program was used to perform statistical analyses.
RESULTS
The κ index for test-retest was 0.80, demonstrating an excellent reliability for mothers’ responses.
The current age was similar between patients with JIA and healthy controls (10.8 ± 3.9 vs 11.2 ± 4.3 yrs). Similarly, the frequency of women (59.1% vs 57.3%) between patients with JIA and healthy controls did not differ. Mean ages at first symptoms and at JIA diagnosis were 5.7 ± 3.9 years and 6.6 ± 3.8 years, respectively. The 66 patients with JIA were classified according to ILAR criteria: 23 (34.8%) were classified as rheumatoid factor (RF)–negative polyarthritis, 4 (6%) as RF-positive polyarticular JIA, 20 (30%) as oligoarticular, 17 (26%) as systemic, and 2 (3%) as other categories (1 psoriatic arthritis and 1 undifferentiated subtype). Anticitrullinated protein antibody was evaluated in 9 patients (13.6%) and it was positive in only 1 case. There were 5 JIA patients who had uveitis prior to joining the study, 2 with oligoarticular JIA, 1 with RF-negative polyarthritis, 1 with systemic JIA, and 1 with psoriatic arthritis.
Table 1 presents gestational, perinatal-related and environmental factors in patients with JIA and healthy controls. The frequency of being in the lower-middle class was significantly higher in patients with JIA compared to healthy controls. The prevalence of intrauterine cigarette smoke exposure in patients with JIA and controls in the lower-middle class was similar to those in the upper classes (36.1% vs 25.6%; p = 0.17). Likewise, the distance to fixed sources of inhalable pollutants was similar in both socioeconomic groups (44.3% vs 55.8%; p = 0.16). No statistically significant differences in ideal maternal weight gain were observed between lower-middle and upper classes (45.9% vs 44.2%). Regarding working, the number of upper-class mothers who worked during pregnancy was significantly higher (75.2% vs 45.9%; p < 0.001); however, maternal occupational exposure was more prevalent in the lower middle class than in the upper classes (21.3% vs 8.5%; p = 0.02).
Gestational, perinatal-related, and environmental factors during gestation affecting patients with JIA and healthy controls. Values are n (%) and mean ± SD.
During pregnancy
Although a smaller number of mothers with JIA worked during pregnancy compared to the number of healthy control mothers (Table 1), the average hours worked per day were similar in both groups. Further, occupational exposure during pregnancy among working mothers with JIA was significantly higher than that for the control working mothers (exposure to fine dust: 23.1% vs 3.0%; p = 0.003, and exposure to volatile vapor: 34.6% vs 7.1%; p = 0.001). In the JIA group, mothers exposed to these substances were employed as teachers (n = 2), seamstresses (n = 4), beauty salon workers (n = 2), copy machine operators (n = 1), and cleaners (n = 6); and in the control group, mothers worked as teachers (n = 2), architects (n = 1), cleaners (n = 6), and copy machine operators (n = 1).
Maternal smoking and exposure to secondhand smoke at home during pregnancy were significantly more prevalent in the JIA group than in the controls (Table 1). The number of mothers who were smoking 1 year prior to the pregnancy was higher among mothers of patients with JIA than among control mothers (22.7% vs 6.5%; p = 0.002).
Regarding gestational and perinatal-related factors, ideal weight gain was lower in the JIA group compared to the controls. There was no significant difference in terms of prematurity or alcohol consumption between the 2 groups.
Distance from home or work to factories or gas stations during pregnancy was similar for patients with JIA and healthy controls, as well as commute time from home to the workplace.
Table 2 shows the results of the univariate logistic regression models for the groups of independent variables related to pregnancy. An association with a significance level < 20% was observed between employment variables, exposure to tobacco, maternal weight gain, prematurity, and home/work distance to environmental sources of inhalable pollutants (gas stations, factories, and quarries). Regarding exposure to tropospheric pollutants during pregnancy, only SO2 in the second trimester was significantly associated with JIA diagnosis.
Exposure to cigarette smoke and inhaled pollutants during gestation as risk factors for JIA in univariate, multilevel, and final multiple logistic regression models.
The results of the multilevel logistic regression approach are shown in Table 2. It was observed that maternal employment, occupational exposure, intrauterine cigarette smoke exposure, and ideal maternal weight gain remained significant, and these variables were included in the final model.
Table 2 also shows the results of a final multiple regression model, including the independent variable groups related to those who presented significance levels < 20% in a univariate model, and statistical significance in multilevel regression. Intrauterine cigarette smoke exposure and maternal occupational exposure remained independent and significant risk factors for JIA, while maternal employment and ideal maternal weight gain had negative associations.
From birth to JIA diagnosis
Table 1 presents data on exposure to cigarette smoke, daycare or school attendance, and environmental factors in patients with JIA and healthy controls.
Secondhand smoke exposure at home after birth was significantly more frequent in the JIA group than in the control group.
Table 3 depicts univariate logistic regression models for groups of independent variables related to the after-birth period. Regarding exposure to tropospheric pollutants by year, only O3 in the second year of life was associated with JIA diagnosis.
Exposure to cigarette smoke and inhaled pollutants after birth as risk factors for JIA in univariate, multilevel, and final multiple logistic regression models.
To define the best indicator of traffic, these variables were included in the multilevel logistic regression analysis: commute time from home to daycare/school and O3 in the second year of life (Table 3). In this approach, only O3 in the second year of life remained significant and was included in the final model, along with the following variables: low/middle socioeconomic status, secondhand smoking, and daycare/school attendance.
The results of the final multiple regression model are shown in Table 3. Secondhand smoking and O3 in the second year of life remained independent and significant risk factors for JIA. However, a negative association between the risk of JIA and daycare/school attendance was observed.
Table 4 demonstrates the final analysis, including all significant variables of the final models in both periods (pregnancy, and from birth to JIA diagnosis) for all patients and JIA categories. We found that only exposure to O3 in the second year of life was a risk factor to disease onset in the systemic JIA group, whereas ideal maternal weight gain and maternal employment during pregnancy remained negatively associated with the risk of systemic JIA. For the other JIA categories (RF-negative polyarthritis and oligoarticular JIA), the results were similar to those analyses performed with the full group.
Exposure to cigarette smoke and inhaled pollutants in both periods (pregnancy, and from birth to JIA diagnosis) as risk factors for JIA for all patients and JIA categories.
DISCUSSION
To our knowledge, ours is the first study to simultaneously analyze the association of outdoor and indoor pollution with JIA diagnosis from pregnancy to disease onset.
Our study has several strengths. It used a structured questionnaire, assessing responses regarding exposure to inhalable environmental pollutants from pregnancy to JIA diagnosis. Additionally, a high κ index for test-retest observed herein indicated that the questionnaire remained consistent in its responses. In contrast to other studies16,18,22,23,24, we evaluated exposure to environmental factors other than cigarette smoke, during pregnancy and up to JIA diagnosis, as a risk factor for disease diagnosis after birth. Relevant issues related to the pregnancy and perinatal period, such as alcohol consumption, prematurity, maternal weight gain, and birth weight were recorded. We also explored maternal occupational exposure to inhalable pollutants and tropospheric pollutants, which were systematically evaluated by automated monitoring stations in São Paulo29.
The main limitation of our study was that the assessment of indoor pollution was based only on cigarette smoke. Other elements, including fuels for household cooking and house dust, were not assessed. Referral bias may exist because we used a convenience sample from a tertiary hospital of patients residing in a metropolitan area. The Pediatric Rheumatology Service of our tertiary university hospital follows up on complex diseases, and many of our patients with JIA (41%) had systemic onset31, which may be a referral bias. There are no nationwide Brazilian data on the prevalence of JIA and its categories. In 1 study, performed in a city in São Paulo state, the prevalence of JIA was reported to be 0.34/1000 children aged 6 to 12 years, a value within the range of reported international JIA prevalence data measurements (0.07 to 4.01/1000 children)32.
In adults with rheumatoid arthritis (RA), exposure to smoking is a consistently identified risk factor33. Because we had only 6% RF-positive JIA, we could not evaluate this category that most mimics adult RA for its cigarette smoke exposure or other exposures in our study.
Although there was a decrease in the number of smoking mothers during pregnancy in both the JIA and control groups, the smoking rate was higher in the JIA mothers during the year prior to pregnancy.
Mothers who smoke during pregnancy may have structural changes in the placenta, as well as decreased levels of placental methylation, and they may transfer to the fetus about 9600 chemicals present in tobacco, such as nicotine and tar34,35. Other studies have also shown an association between mothers who smoked during pregnancy and DNA methylation20,36,37,38. However, previous studies demonstrating an association between JIA onset and cigarette smoke exposure during pregnancy remain controversial22,23,24,39. In 2 studies, Shenoi, et al did not find evidence of an association between JIA and maternal prenatal smoking22,23; nevertheless, Jaakkola and Gissler found a higher positive association with chronic polyarthropathy in children with JIA whose mothers had smoked > 10 cigarettes per day during pregnancy compared to nonsmoking mothers, although this effect was limited to girls24. Our results were almost similar to Jaakkola and Gissler’s suggestion that exposure to cigarette smoke during pregnancy increases the risk of JIA in the long term. Further, our study evaluated exposure to cigarette smoke in both periods, during pregnancy and from birth to JIA diagnosis, and it was observed that longterm exposure to cigarette smoke was an important risk factor for all JIA categories studied. However, we did not observe an association between the number of cigarettes and JIA diagnosis. Further studies will be necessary to identify whether total duration or total dose is the most important risk factor.
Unexpectedly, we observed a negative association between maternal employment and JIA diagnosis during pregnancy. However, a positive association was observed among working mothers, in particular those exposed to chalk powder, cleaning products, sewing dust, and volatile vapor. Lower socioeconomic status might be associated with occupations in which exposure to environmental toxicants is higher. However, in our multivariate analysis, low/middle socioeconomic status was not associated with, and did not modify the positive association between, maternal occupational exposure and JIA diagnosis.
Maternal occupational exposure has not been previously studied in JIA. In addition, some studies observed a positive association between maternal occupational exposure and childhood chronic diseases, such as leukemia40,41, non-Hodgkin lymphoma40, and juvenile dermatomyositis17. It may thus be inferred, based on the literature and on our results, that working during pregnancy is not a matter of concern, but occupational exposure to inhalable toxic pollutants may play a role in JIA pathophysiology.
Moreover, we observed that ideal maternal weight gain during pregnancy was a protective factor for JIA. To our knowledge, this association had never been evaluated, and further studies are necessary to confirm this finding.
In our analysis regarding the period from birth to JIA diagnosis, the association with secondhand smoke exposure remained relevant. In RA, the association with smoking is well established32,42,43,44. Smoking and other inhalable proinflammatory agents may play a role in stimulating protein citrullination in the lungs, mediated by peptidylarginine deiminase enzymes, and may induce autoantibodies. In genetically predisposed individuals, protein citrullination affects the potential risk of anticitrullinated peptide autoantibody production34. These findings have not been studied among JIA populations, to our knowledge.
Studies evaluating the effects of exposure to tropospheric pollution on autoimmune inflammatory diseases have multiplied in the last decade, mainly with adults2,3,11,13,14,15. Outdoor air pollution studies on pediatric rheumatologic diseases are rare4,15,16,17,18,19. Zeft, et al found a high risk of JIA development in children under 5 years associated with higher concentrations of PM2,5 and stagnant air conditions in the 14 days preceding JIA diagnosis16. This study is different from our study, which evaluated longterm exposure to tropospheric pollutants. Specifically, in the case of exposure to O3, there is sparse evidence of morbidity in longterm exposure cases. De Roos, et al demonstrated that longterm exposure to O3 was a risk factor for RA11. In our study, exposure to O3 in the second year of life represented a high risk for developing both overall and systemic JIA. Based on our results, we can speculate that exposure in the first 2 years of life to environmental toxicants that are proinflammatory may be a factor in the pathogenesis of JIA. One possible explanation for the extrapulmonary effects is the release of oxidative products into circulation originating from O3 effects on the lungs, leading to arterial endothelial damage. Damaged epithelial cells release other mediators into the blood that can activate a systemic inflammatory response45,46. The combination of damaged arterial endothelium and systemic inflammation can alter methylation at protein binding sites in DNA, leading to autoimmunity47,48,49.
Regarding the after-birth period, the only negative association with JIA development observed in our study was daycare/school attendance. Shenoi, et al23 also evaluated this characteristic and no association with JIA diagnosis was found. Hence, a negative association between the mother’s employment and JIA diagnosis during pregnancy should be interpreted with caution, and more studies will be necessary.
Our study identified exposure to cigarette smoke either in utero or after birth as a risk factor associated with JIA. Our results are sufficiently compelling to warrant future studies to investigate the potential role of maternal occupational and air pollutant exposure in the pathogenesis of JIA.
Footnotes
Supported by grants from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq 472155/2012-1 to CAS and 302724/2011-7 to CAS), Federico Foundation (to CAS), and by Núcleo de Apoio à Pesquisa “Saúde da Criança e do Adolescente” da USP (NAP-CriAd) to CAS.
- Accepted for publication September 8, 2017.
