Occupation exposed to road-traffic emissions and respiratory health among Congolese transit workers, particularly bus conductors, in Kinshasa: a cross-sectional study
Mbelambela et al. Environmental Health and Preventive Medicine
Occupation exposed to road-traffic emissions and respiratory health among Congolese transit workers, particularly bus conductors, in Kinshasa: a cross-sectional study
Etongola Papy Mbelambela 0
Ryoji Hirota 0
Masamitsu Eitoku 0
Sifa Marie Joelle Muchanga 0 2
Hidenori Kiyosawa 0
Kahoko Yasumitsu-Lovell 0 1
Ontshick Leader Lawanga 3
Narufumi Suganuma 0
0 Department of Environmental Medicine, Kochi University Medical School , Oko-cho Kohasu, Nankoku, Kochi 783-8505 , Japan
1 Gillberg Neuropsychiatry Centre, University of Gothenburg , Gothenburg , Sweden
2 Department of Gynecology and Obstetrics, University of Kinshasa , Kinshasa , Democratic Republic of the Congo
3 Department of Mathematic, University of Kinshasa , Kinshasa , Democratic Republic of the Congo
Objectives: Road-traffic emissions (RTE) induce adverse health effects, notably respiratory symptoms and respiratory diseases, as a result of pollutants deposited into the respiratory tract. The aim of this study was to evaluate the association between occupation groups of Congolese transit workers exposed to RTE, particularly bus conductors and respiratory health, in Kinshasa. Methods: A cross-sectional study was conducted from 2015 April 20th to May 14th, whose participants were bus conductors (n = 110), bus drivers (n = 107), taxi-motorcyclists (n = 102) and high school teachers (control group; n = 106). Subjects had completed the American Thoracic Society respiratory symptom questionnaire. Lung function test was performed by spirometry. Air pollutants levels of PM2.5, NO2 and SO2 were measured between 7:30 and 8:30 and 16:30-17:30 using a portable gas monitor. Multivariate analysis was performed to evaluate the association between occupation exposed to RTE and impaired pulmonary function, after adjustment by plausible confounders. Results: The prevalence of mixed syndrome was 21.9% for bus conductors, 10.9% for bus drivers, 15.4% for taxi-motorcyclists and 7.1% for high school teachers with (p < 0.05). The risk of developing a mixed syndrome was seven times higher among bus conductors [OR = 7.64; 95% CI: 1.83-31.67; p < 0.05] than other groups. Additionally, the prevalence of respiratory syndromes increased with the duration of exposure. Conclusions: Occupation exposed to RTE is associated with impaired pulmonary function and the prevalence of respiratory symptoms among transit workers, especially bus conductors. Furthermore, this association increases with the duration of exposure suggesting the necessity to regulate these categories of occupations and to apply preventives measures.
Bus conductors; Respiratory health; Road traffic emissions; Transit workers
In the coming decades, road transport is likely to remain
a significant contributor to air pollution in most of cities.
Many urban trips cover distances shorter than 6 km and
the average traffic emissions per driving distance are
very high in urban areas due to the low effectiveness of
catalytic converters in the initial minutes of engine
operation. Also, poorly maintained vehicles that lack exhaust
after treatment systems are responsible for a major part
of pollutant emissions . Preliminary assessments
indicate that, each year, ten thousands persons are
affected by diseases related to road-traffic emissions in
the European region .
Road-Traffic Emissions (RTE) has been associated to
different sources. Among them, exhaust pipe emissions,
contributions from friction processes and resuspended
road dust are known to have adverse health effects, such
as throat pain, phlegm, chronic rhinitis and chronic
pharyngitis among bus drivers, bus conductors and taxi
drivers [3, 4]. The pollutants of greatest concern, due to
their impact over health, are particulate matter (PM),
ground-level ozone (O3), NO2, carbon monoxide (CO)
and volatile organic compounds (VOC). One of the most
important sectors that produce these pollutants is
related to the transportation sector [5, 6].
In developed countries, some studies related to
exposure to air pollution and adverse health outcomes have
shown an increase of decease for stomach cancer, lung
cancer, bronchitis, emphysema and asthma. In addition,
Buckeridge et al., in the Toronto study had shown a high
prevalence of bronchitis, pneumonia, chronic obstructive
pulmonary disease and hospital admissions for exhibited
individuals . Furthermore, the exposure to
trafficrelated pollutants such as diesel exhaust particles (DEP)
or NO2 may contribute to increased respiratory morbidity
among adolescents, urban residents and asthmatics. Also,
this exposure has been correlated to an increased risk of
chronic obstructive pulmonary diseases among railroad
workers exposed [8, 9].
A long-term exposure to traffic and PM2.5 at relatively
low levels concentration (μg/m ) were reported to be
associated with lower forced expiratory volume in first
second (FEV1) and forced vital capacity (FVC). In
addition, a marked decrease in lung function rate and a
high blood pressure were observed in the Veterans
Administration Normative Aging Study [10, 11]. Research
conducted in the Sub-Saharan African countries
regarding the effects of air pollutants among traffic workers
and non-traffic workers also showed similar health
outcomes [3, 4, 12]. However, the lack of studies related to
occupation groups of transit workers exposed to RTE
and respiratory health in the Democratic Republic of
Congo (DRC), remains a matter of making the
comparative results with previous studies. Actually, transit workers
group of bus conductors constitutes one of vulnerable
population. Their vulnerability is mainly due to the
exhaust pipe emissions inhaled when calling, persuading
potential clients and their outside position during the
round (Fig. 1). Majority of them consists of young people,
with low education level, low socio-economic status and
without health insurance coverage.
No official or national records about socio-economic
profiles, literacy rates and educational level have been
taken in this population. The aim of this study was to
evaluate the association between occupation groups of
Congolese transit workers exposed to RTE, particularly
bus conductors and the respiratory health, in Kinshasa,
the capital of DRC.
Fig. 1 Bus conductors outside of micro bus during the round in Kinshasa, Democratic Republic of the Congo
Materials and methods
Study design and participants
A cross-sectional study was conducted in Kinshasa,
DRC, from 2015 April 20th to May 14th. A total of 517
subjects, including 392 RTE-exposed transit workers
(138 bus conductors, 138 bus drivers, 116 taxi
motorcyclists) and 125 high school teachers (control group) were
enrolled in this study. Among the enrolled, 31 subjects
did not meet the required conditions for spirometry
performance, 33 spirometry items were unacceptable,
and 28 questionnaires had a missing data. Finally 425
subjects were eligible for this study, including, 110 bus
conductors, 107 bus drivers, 102 taxi motorcyclists and
106 high school teachers.
The inclusion criteria were: males, between 20 and 40
years old, who have been working at least three years
before prior survey. The exclusion criteria were: females,
history of active chronic lung disease or lung surgery and
under corticosteroid therapy or beta mimetic-medication.
Ethical considerations and data collection
The study protocol was approved by the Environment
Department of the Provincial Government of Kinshasa,
DRC and the ethics committee of Kochi University Medical
School, Japan (approval number: 2015–007). After a
thorough explanation of the study content, a written informed
consent was obtained from each participant.
A translated French version of the American Thoracic
Society respiratory symptom questionnaire (ATS) was
anonymously completed by all participants to assess
respiratory health . Given the low literacy of some of
the participants, the questionnaire was administered
with assistance of surveyors (three medical doctors and
one nurse). Information on respiratory symptoms,
personal and familial medical history, lifestyle, employment
history, socio-economic status, smoking status, alcohol
consumption, physical activity and household
characteristics were collected.
The anthropometric parameters (height, weight), blood
pressure, lung function parameters were assessed.
Body weight of each subject was measured using the scale
Omron HBF-217 (Karada scan, Kyoto Japan) by following
instructions from the manufacturer. Body height
measurement was assessed using Microtoise Seca 206 (Japan).
Body mass index (BMI) was calculated and classified
according to WHO guidelines for BMI .
Blood pressure measurement was performed by the
use of an electronic sphygmomanometer typed Omron
HEM-6200 (Japan) following the recommendation of
the American Heart Association and Joint National
Committee for management of hypertension in adult
(JNC-8) [15, 16].
Lung function testing (spirometry)
Before spirometry performance, surveyors explained the
importance and the procedure of the test. Participants
were asked to follow these recommendations: no heavy
physical exercises 30 min, no corticoid medication 24 h, no
cigarette smoking 1 h, no heavy meal 2 h, and no alcohol
consumption 4 h before the test.
From 2015 April 20th to May 14th twice a day between
12 h30 and 14 h30 and 4 h30-6 h30 PM for participant
units of 15–20 individuals, Forced vital capacity (FVC),
forced expiratory volume in first second (FEV1) and
FEV1/FVC ratio was measured using an Autospiro
Minato AS-470 (Medical Science Company Ltd, Osaka)
spirometry after calibration.
The recommendations of ATS on acceptability and
reproducibility of the test were followed including: the
duration of exhalation at least 6 s for adults, the FVC
and FEV1 were measured through a series of three
acceptable items free from artifacts in each participant; the
effort provided by the subject was reproductive and
maximum. The change in lung function (△FVC and
△FEV1) which is defined as the difference in the lung
function between the last observation and the first
observation was less than 200 mm .
Spirometry measured values of FVC and FEV1 were
compared with predicted normal values based on the
regression equation from National health and nutrition
examination survey (NHANES III)/Hankinson et al.
1999 for male American-African :
FVC ¼ −0:1933 þ 64:10−5
age þ 186:10−5
FEV1 ¼ 0:5536−13:10−3
þ 14:10−5 heightðcmÞ
FEV1% ¼ PredictedFEV1=Predicted FVC
The impaired pulmonary function was calculated in
accordance with the ATS guidelines, as follows:
1. Obstructive syndrome defined by: FEV1/FVC ratio
<70% of predicted.
2. Restrictive syndrome defined by: FEV1/FVC ratio is
normal or increase and FVC < 80% of predicted.
3. Mixed syndrome defined by combination of restrictive and obstructive syndrome abnormalities.
Ambient Air measurements
Choice of locations is related to geographical, traffic
volume and administration distribution of Kinshasa.
Location 1 is the road that goes from East to down town
with four lanes, fourteen intersections, and fourteen bus
stops. Location 2 is the road that goes from western to
down town with four lanes, twelve intersections, and
eighteen bus stops. Location 3 is the road that goes from
south to down town with eight lanes, sixteen
intersections, twenty two bus stops and eight bus stations.
Location 4 is the road that goes from North to down town
with eight lanes, fourteen intersections, sixteen bus stops
and nine bus stations.
Outdoor PM2.5 (μg/m3) was assessed at each location
at 50 m around the road intersections using the Digital
dust indicator cyclone LD-5, a portable gas monitor
(Sibata kagaku, Japan), NO2 was measured using the Gas
Alert extreme GAXT-D-DL 2313, Single-Gas Detector,
(BW Technologies, USA), and Sulfur Dioxide (SO2)
using Gas Alert extreme GAXT-S-DL 0515, single-Gas
Detector (BW Technologies, USA). All measurements
were performed between 7 h30 and 8 h30 and 16
h3017 h30 at four locations with the same instruments.
Each value for every location was represented by an
average of different intersections in the same location.
Air quality guidelines of World Health Organization
were used as reference values .
To assess the air quality in the bus, a portable monitor
gas was placed inside and in front of the bus after
closing the windows, doors and stopping the air conditioner.
Measurements for high school teachers were taken in
Traffic volume measurements were also measured, and
meteorological parameters (temperature, wind speed, wind
direction, humidity, and precipitation) were provided from
the regional meteorological agency of Kinshasa, DRC.
To test the intergroup differences, Chi-square test and
analysis of variance (ANOVA) were performed for
categorical and numerical variables respectively. The results
were summarized in tables and graphics. Continuous
variables were represented by mean and standards
deviation (mean; SD) and categorical variables were
represented by proportion (%).
Univariate analysis was carried out to evaluate the
association between different risk factors and impaired
pulmonary function. Multivariate analysis was performed to
evaluate the association between occupation group
exposed to RTE and impaired pulmonary function, after
adjustment for age, BMI, working years, physical activity,
alcohol consumption, smoking status, and personal
medical history. Results were presented as adjusted odds ratio
(aOR), confidence interval (CI).
Statistical significance was defined as a 2-sided P value
less than 0.05. All analyses were performed using STATA
Software version 13.0 for windows.
In total, 425 subjects participated in this study (110 bus
conductors, 107 bus drivers, 102 taxi motorcyclists, and
106 teachers of high school). Baseline characteristics of
the study population are shown in Table 1. The
meanage was 26.6 (4.2) years for bus conductors, 29.9 (6.2)
for bus drivers, 29.2 (7.2) for taxi motorcyclists and 32.3
(5.6) for teachers with p < 0.001. 32. 7% of bus
conductors, 64.5% of bus drivers, 20.6% of taxi motorcyclists
and 30.2% of high school teachers had worked for at
least 5 years with p < 0.001. Current smokers
represented 79% of bus conductors, 71% of bus drivers, 40%
of taxi motorcyclists and 24% of high school teachers
with p < 0.001.
Concentration of PM2.5 was: 128.7 ± 3.40 μg/m3, 112.3
± 4.43 μg/m3, 73.7 μg/m3 ± 3.13, and 64.2 μg/m3 ± 2.01
in location1, 2, 3, and 4 respectively. Whereas NO2
concentration was: 135.9 ± 2.16 μg/m3, 124.1 ± 6.73 μg/m ,
119.6 ± 2.55 μg/m3, and 112.9 ± 2.96 μg/m3, in location1,
2, 3 and, 4 respectively (Fig. 2).
Prevalence of respiratory symptoms was statistically
significant in the study groups with p < 0.001, except for
the morning cough. For impaired pulmonary function,
21.9% of bus conductors, 10.9% of bus drivers, 15.4% of
taxi motorcyclists and 7.1% of high school teachers had
mixed syndrome with p < 0.05 reported in the Table 2.
Risk of impaired pulmonary function related to
working year or duration of exposure was OR 4 (95% CI 2.11,
7.58) for bus conductors, OR 4.37 (95% CI 2.20, 8.69)
for bus drivers, OR 4.53 (95% CI 2.35, 8.72) for taxi
motorcyclists, OR 2.63 (95% CI 1.91, 6.90) for high school
teachers (results not shown).
Morning cough was associated with bus conductors
occupation, aOR 2.94 (95% CI 1.30, 6.64) and bus drivers,
aOR 2.39 (95% CI 1.04, 5.48). In addition, a significant
association with mixed syndrome, aOR 7.64 (95% CI 1.83,
31.67) was found for bus conductors. Whereas, restrictive
syndrome, aOR 3.22 (95% CI 1.35, 7.69) was associated
with taxi motorcyclists occupation (Table 3).
Few studies have examined the potential role of RTE as
a risk factor of impaired pulmonary function among the
transit workers, particularly bus conductors.
The present research has assessed the relationship
between occupation exposed to road-traffic emissions and
respiratory health of Congolese bus conductors, bus
drivers, and taxi-motorcyclists in Kinshasa.
To our knowledge, this study is the first to evaluate
the respiratory health of these exposed groups in DRC.
After adjusting for a number of potential confounders,
findings are depicted as follow:
1. Air pollutants measurements (PM2.5, NO2, and SO2)
in outdoor, in bus, in classroom were higher than
the normal range of World Health Organization
Table 1 General characteristics of the study population
Characteristics Bus conductors
n = 110
Age (year) Mean (SD) 26.6 (4.2)
BMI (Kg/m2) Mean (SD)
SBP (mmHg) Mean (SD)
DBP (mmHg) Mean (SD)
Education level n (%)
Working year n (%)
Smoking status n (%)
Passive smoking at workplace
Alcohol consumption n (%)
Physical activity n (%)
Personal medical history n (%)
FEV1 Mean (SD)
FEV1% of predicted Mean (SD)
FVC% of predicted Mean (SD)
2. The prevalence of respiratory symptoms was higher in the exposed groups (bus conductors, bus drivers, taxi motorcyclists) than the control group (high school teachers).
3. Exposed groups had a decreased lung function and greater at risk to impaired pulmonary function than control group.
4. Exposed groups who worked for five years or more were at greater risk to impaired pulmonary function and they presented more pulmonary symptoms than the control group.
Our study reports that the level of outdoor PM2.5,
NO2, and SO2 in different selected locations was higher
than the normal range of the WHO guidelines. Thus, the
maximum concentration of PM2.5 found was 134 μg/m3
and the minimum concentration was 62 μg/m3.
Furthermore, the average concentration of PM2.5 was 94.72 ±
27.49 μg/m3 in selected locations. This value is close to
the concentrations above 100 μg/m3 in Kampala, Uganda
and 128.04 μg/m3 in Delta Niger, Nigeria [12, 20].
Although the methods of assessment were different;
Uganda’s study used the permanent station monitor
Fig. 2 Pollutants concentration in different locations. Particulate matter 2.5 (PM2.5 μg/m3), Nitrogen dioxide (NO2 μg/m3), Sulfur dioxide (SO2 μg/m3),
Microgram per cubic meter (μg/m3)
whereas our study the fact of limiting the financial
support and Nigeria’s study used portable gas monitor.
That DRC, Uganda and Nigeria are developing
countries with lack of good policies in environment
management could explain these similar results.
Our study found that bus conductors and bus drivers
were more exposed to particulate matter than high
school teachers (results not shown).
Similar results were reported by Krzyzanowski M
et al., in Copenhagen, and two other studies in Taipei
and in Madrid where the people use motorcycles on
road, bus/mass rapid transit commuters walk or wait
along commuting routes have exhibited to high personal
particulate matter exposure due to the traffic-volume
and environmental factors contributed in the high
personal particulate matter exposure for people use
motorcycles [1, 21, 22].
In our study the prevalence of almost all respiratory
symptoms was significantly higher in the exposed group
than the control group. Similar results were reported by
Zuskin et al., comparing drivers, mechanics compared
with office workers .
Exposure to RTE increased the burden of environment
and induced respiratory symptoms in exposed groups
than the control groups. Same results were reported at
different places around the world by Schwander S et al.,
in Kampala, by Zhou et al., in Shanghai, by Karita K
et al., in Bangkok and by Estevez-Gracia JA et al., in
Table 2 Prevalence of respiratory symptoms in the study population
At least 4 days a week
At least 4 days a week
Wheezing > 16y old
Chi square test, y year, % percent, p < 0.05
Table 3 Multivariate analysis of association between occupation groups, respiratory symptoms and respiratory impaired function
At least 4 days a week
At least 4 days a week
Wheezing > 16 y-old
Impaired pulmonary function
2.94 (1.30, 6.64)**
4.87 (2.51, 9.45)**
4.66 (1.70, 12.79)**
7.46 (3.41, 16.30)**
3.13 (1.25, 7.80)*
7.64 (1.83, 31.67)*
4.49 (0.70, 28.56)
2.39 (1.04, 5.48)*
4.40 (2.25, 8.58)*
5.23 (2.36, 11.58)*
0.23 (0.60, 0.91)*
3.30 (1.67, 6.53)*
3.52 (1.30, 9.54)*
3.8 (1.72, 8.74)*
3.22 (1.35, 7.69)*
2.61 (0.67, 10.08)
2.90 (0.56, 14.97)
aOR adjusted odds ratio for Age, BMI, working year, smoking status, alcohol consumption, physical activity, personal respiratory history,
CI confidence interval, y, year, *p < 0.05, **p < 0.01
Bogota [3, 24–26]. The same trend was reported by
Brant TC in Saopaulo, even in the general population
and no-smoking commercial motorcyclists .
In contrast: Studying the prevalence of respiratory
symptoms in 7,154 state road transport workers in India,
Monica B et al., found that the prevalence of respiratory
symptoms were significantly higher in office workers
(34.9%) as compared to drivers (24.2%), conductors
(25.4%), and 30.0% in garage workers . Also, Biqert C
et al. reported that a short- term exposure to fractional
exhaled nitric oxide did not affect the pathway of the
exhibited subway workers airway or their lung function .
Type of location, characteristics of population, method
used for measurement, time of exposure, the
composition and concentration of ambient pollutants,
susceptibility of given population to oxidative stress, workplace
condition could explain the different results in the
similar epidemiological studies.
Present research has shown that the prevalence of
mixed syndrome was 21.9% for bus conductors and
10.9% for bus drivers and restrictive syndrome was
27.3% for bus conductors, 23.2% for bus drivers. These
results are close to the study conducted by
Chattopadhyay BP et al., who found that the impaired pulmonary
function was associated with exposure to automobile
exhaust, especially, 30.4% at risk of developing the
restrictive syndrome for conductors and 28.9% for drivers .
Similar results in the decrease of pulmonary function
associated to traffic-related air pollution were reported in
Mexican, Indian and in Danish studies [31–33].
Our study has reported that, after adjusting for
confounding factors, occupation exposed to RTE were
associated with mixed syndrome and restrictive
syndrome, especially among bus conductors and taxi
motorcyclists. Bus conductors were seven times at risk to
develop mixed syndrome with aOR: 7.64 (95% CI 1.83,
31.67), whereas taxi motorcyclists were three times at
risk of developing restrictive syndrome with aOR: 3.22
(95% CI 1.35, 7.69). Indeed, the Congolese policy in the
transportation sector requires maintenance time be
respected, the wearing of a crash helmet by
motorcyclists also, prohibits bus conductors to be outside the
bus but the applicability of those measures is not
effective, this make transit workers in Kinshasa more
vulnerable to the impaired respiratory function. Framingham
heart study reported the close results that the decline of
lung function was associated with a long term exposure
to traffic and PM2.5 at relatively low levels concentration
(μg/m3) . Additionally, our research shows that
occupation exposed groups who worked for five years or
more have presented four times at risk of developing
impaired pulmonary function. High school teachers group
had more than twice at risk of developing impaired
pulmonary function. Similar results were found in Nigerian
transit workers, worked for five years . Whereas,
Croatian study has found that this association was
significant among exhibited bus drivers and mechanics
employed for more than 10 years .
Otherwise, the fact that the most of developing
countries like DRC, the high school teachers use continuously
a piece of chalk with the black board and inhale the dust
releases by this process, is a plausible explanation of
impaired respiratory function in this group. Little is known
on the exact mechanism of impaired respiratory function
according to exposure to traffic-related air pollution
. Our study as several others would support the
assumption of part of oxidative stress and inflammation in
the alteration of respiratory function and partial
obstruction of pathway [34, 35].
Strengths and limitations
This is the first study elucidated the association between
occupation groups of transit workers exposed to RTE
and impaired respiratory function in the Democratic
Republic of the Congo, using the American Thoracic
Society respiratory symptoms questionnaire and spirometry.
Also the present study has assessed traffic volume and
air pollutants measurements (PM2.5, NO2 and SO2)
outdoor, in the bus, in the classroom.
Despite these strengths, the study has some limitations;
First, a cross-sectional design that could not establish
the causal relationship between the exposed groups and
the occurrence of pulmonary function decline.
Second, the measurements of pollutants were carried
out at selected locations limiting the generalization of the
results to other geographic locations with very different
engine, fuels used, topography and workplace condition.
Third, the pollutants (PM2.5, NO2, and SO2) were
measured by a portable gas monitor. The use of a
spatialtemporal land model, instead of portable gas monitor
would have provided more accurate information on each
participant. Finally, no data on residential history of the
participant or on the time spent outside were collected.
As conclusions, the present study found an association
between occupation groups of transit workers exposed
to RTE and impaired pulmonary function, with a
greatest risk of mixed syndrome among bus conductors and a
risk of restrictive syndrome among both bus conductors
and taxi motorcyclists. Also, prevalence of impaired
pulmonary function increased with working length. Hence the
imperative needs to regularize this category of profession
and apply important preventive policy. Follow up study is
needed to establish the evidence of causal relationship.
EPM Principal investigator and designer of the study, participated in
statistical analyses, revised the manuscript, and approved the final version of
manuscript. RH participated in research designing, statistical analysis, and
wrote the manuscript, approved the final version of manuscript. ME
participated in study design, data analysis interpretation, drafting and
approval of the final version of manuscript. MSM participated in research
designing, statistical analysis, approval of the final version of manuscript. HK
participated in statistical analysis, written manuscript approval of the final
version of manuscript. KY-L participated in statistical analysis, approval of the
final version of manuscript. LOL participated in data collection, approval of
the final version of manuscript. NS professor, advisor of research, participated
in research designing, statistical analysis, improved and approval the final
version of the manuscript. All authors read and approved the final
The authors declare that they have no competing interests.
Ethics approval and consent to participate
This study is in accordance with the ethical standards.
Springer Nature remains neutral with regard to jurisdictional claims in published
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1. Krzyzanowski M , Kuna-Dibbert B , Schneider J. Health effects of transportrelated air pollution: Europe: World Health Organization Regional Office; 2016 . pp. 7 - 9 . http://www.euro.who.int/__data/assets/pdf_file/0006/74715/ E86650.pdf.
2. Kunzli N , Kaiser R , Medina S , et al. Public-health impact of outdoor and traffic-related air pollution: a European assessment . Lancet . 2000 ; 356 ( 9232 ): 795 - 801 .
3. Zhou W , Yuan D , Ye S , Qi P , Fu C , Christiani DC . Health effects of occupational exposures to vehicle emissions in Shanghai . Int J Occup Environ Health . 2001 ; 7 ( 1 ): 23 - 30 .
4. Hoek G , Brunekreef B , Goldbohm S , Fischer P , van den Brandt PA. Association between mortality and indicators of traffic-related air pollution in the Netherlands: a cohort study . Lancet . 2002 ; 360 ( 9341 ): 1203 - 9 .
5. WHO. WHO | Ambient (outdoor) air quality and health . Available at: www. who.int/mediacentre/factsheets/fs313/en/. Accessed 2016 .
6. Balarajan R , McDowall ME . Professional drivers in London: a mortality study . Br J Ind Med . 1988 ; 45 ( 7 ): 483 - 6 .
7. Buckeridge DL , Glazier R , Harvey BJ , Escobar M , Amrhein C , Frank J. Effect of motor vehicle emissions on respiratory health in an urban area . Environ Health Perspect . 2002 ; 110 ( 3 ): 293 - 300 .
8. Patel MM , Chillrud SN , Correa JC , et al. Traffic-related particulate matter and acute respiratory symptoms among New York City area adolescents . Environ Health Perspect . 2010 ; 118 ( 9 ): 1338 - 43 .
9. Hart JE , Laden F , Schenker MB , Garshick E. Chronic obstructive pulmonary disease mortality in diesel-exposed railroad workers . Environ Health Perspect . 2006 ; 114 ( 7 ): 1013 - 7 .
10. Rice MB , Ljungman PL , Wilker EH , et al. Long-term exposure to traffic emissions and fine particulate matter and lung function decline in the Framingham heart study . Am J Respir Crit Care Med . 2015 ; 191 ( 6 ): 656 - 64 .
11. Schwartz J , Alexeeff SE , Mordukhovich I , et al. Association between long-term exposure to traffic particles and blood pressure in the Veterans Administration Normative Aging Study . Occup Environ Med . 2012 ; 69 ( 6 ): 422 - 7 .
12. Ekpenyong CE , Ettebong EO , Akpan EE , Samson TK , Daniel NE . Urban city transportation mode and respiratory health effect of air pollution: a crosssectional study among transit and non-transit workers in Nigeria . BMJ Open . 2012 ; 2 ( 5 ).
13. Society AT . Recommended respiratory disease questionnaires for use with adults and children in epidemiological research . Am Rev Respir Dis . 1978 ; 118 : 7 - 53 .
14. World Health Organization. Global database on body mass index . 2016 . from: apps . who.int/bmi/index.jsp?introPage=intro_3 .html.
15. Pickering TG , Hall JE , Appel LJ , et al. Recommendations for blood pressure measurement in humans and experimental animals: Part 1: blood pressure measurement in humans: a statement for professionals from the Subcommittee of Professional and Public Education of the American Heart Association Council on High Blood Pressure Research . Hypertension. 2005 ; 45 ( 1 ): 142 - 61 .
16. Armstrong C. JNC8 guidelines for the management of hypertension in adults . Am Fam Physician . 2014 ; 90 ( 7 ): 503 - 4 .
17. Pellegrino R , Viegi G , Brusasco V , et al. Interpretative strategies for lung function tests . Eur Respir J . 2005 ; 26 ( 5 ): 948 - 68 .
18. Hankinson JL , Odencrantz JR , Fedan KB . Spirometric reference values from a sample of the general U .S. population. Am J Respir Crit Care Med . 1999 ; 159 ( 1 ): 179 - 87 .
19. Krzyzanowski M. WHO Air Quality Guidelines for Europe . J Toxicol Environ Health A . 2008 ; 71 ( 1 ): 47 - 50 .
20. Kirenga BJ , Meng Q , van Gemert F , et al. The state of ambient air quality in Two Ugandan cities: a pilot cross-sectional spatial assessment . Int J Environ Res Public Health . 2015 ; 12 ( 7 ): 8075 - 91 .
21. Tsai DH , Wu YH , Chan CC. Comparisons of commuter's exposure to particulate matters while using different transportation modes . Sci Total Environ . 2008 ; 405 ( 1-3 ): 71 - 7 .
22. Perez-Martinez PJ , Miranda RM . Temporal distribution of air quality related to meteorology and road traffic in Madrid . Environ Monit Assess . 2015 ; 187 ( 4 ): 220 .
23. Zuskin E , Mustajbegovic J , Schachter EN . Respiratory symptoms and lung function in bus drivers and mechanics . Am J Ind Med . 1994 ; 26 ( 6 ): 771 - 83 .
24. Schwander S , Okello CD , Freers J , et al. Ambient particulate matter air pollution in Mpererwe District, Kampala, Uganda: a pilot study . J Environ Public Health . 2014 ; 2014 : 763934 .
25. Karita K , Yano E , Tamura K , Jinsart W. Effects of working and residential location areas on air pollution related respiratory symptoms in policemen and their wives in Bangkok , Thailand. Eur J Public Health . 2004 ; 14 ( 1 ): 24 - 6 .
26. Estevez-Garcia JA , Rojas-Roa NY , Rodriguez-Pulido AI . Occupational exposure to air pollutants: particulate matter and respiratory symptoms affecting traffic-police in Bogota . Rev Salud Publica (Bogota) . 2013 ; 15 ( 6 ): 889 - 902 .
27. Brant TC , Yoshida CT , Carvalho Tde S , et al. Mucociliary clearance, airway inflammation and nasal symptoms in urban motorcyclists . Clinics (Sao Paulo) . 2014 ; 69 ( 12 ): 867 - 70 .
28. Barne M , Apte K , Chhowala S , Pachisia B , Brashier B , Madas S , et al. Prevalence of respiratory symptoms in 7154 state road transport workers from India . Eur Respir J . 2011 ; 38 (Suppl 55): 4192 .
29. Bigert C , Alderling M , Svartengren M , Plato N , Gustavsson P. No short-term respiratory effects among particle-exposed employees in the Stockholm subway . Scand J Work Environ Health . 2011 ; 37 ( 2 ): 129 - 35 .
30. Chattopadhyay BP , Alam J , Roychowdhury A. Pulmonary function abnormalities associated with exposure to automobile exhaust in a diesel bus garage and roads . Lung . 2003 ; 181 ( 5 ): 291 - 302 .
31. Cortez-Lugo M , Ramirez-Aguilar M , Perez-Padilla R , Sansores-Martinez R , Ramirez-Venegas A , Barraza-Villarreal A. Effect of personal exposure to PM2.5 on respiratory health in a Mexican panel of patients with COPD . Int J Environ Res Public Health . 2015 ; 12 ( 9 ): 10635 - 47 .
32. Ajay K , Vatsala A , Sangam J. Comparative study of PEFR between Auto drivers with the residents of Urban Davangere . Pharm Sci Res . 2014 ; 6 : 226 - 8 .
33. Wurtz ET , Schlunssen V , Malling TH , Hansen JG , Omland O. Occupational chronic obstructive pulmonary disease in a Danish population-based study . COPD . 2015 ; 12 ( 4 ): 435 - 43 .
34. Cavan DA , Parkes A , O'Donnell MJ , Freeman W , Cayton RM . Lung function and diabetes . Respir Med . 1991 ; 85 ( 3 ): 257 - 8 .
35. Ofulue AF , Thurlbeck WM . Experimental diabetes and the lung . II. In vivo connective tissue metabolism . Am Rev Respir Dis . 1988 ; 138 ( 2 ): 284 - 9 .