|Year : 2018 | Volume
| Issue : 3 | Page : 149-155
Lung function abnormalities among garri processing workers in Ogbomoso, Nigeria
Taofeek Oloyede1, Adeseye Abiodun Akintunde2, Jamiu A Adeniran3, Moses O Tanimowo2, Emmanuel Ademola Fawibe4, Alakija Kazeem Salami5
1 Department of Medicine, Ladoke Akintola University of Technology Teaching Hospital, Ogbomoso, Oyo State, Nigeria
2 Department of Medicine, Ladoke Akintola University of Technology Teaching Hospital; Department of Medicine, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria
3 Department of Chemical Engineering, University of Ilorin, Ilorin, Kwara State, Nigeria
4 Department of Medicine, University of Ilorin, Ilorin, Kwara State, Nigeria
5 Department of Medicine, Ladoke Akintola University of Technology Teaching Hospital, Ogbomoso, Oyo State; Department of Medicine, University of Ilorin, Ilorin, Kwara State, Nigeria
|Date of Web Publication||26-Sep-2018|
Adeseye Abiodun Akintunde
P. O. Box 3238, Osogbo, Osun State
Source of Support: None, Conflict of Interest: None
Background: Local production of garri (cassava crisps) is associated with air pollution and consequently lung function abnormalities among garri processing workers. This study was aimed at describing lung function abnormalities among Nigerians engaged in cassava crisps (garri) processing. Methods: A total of 351 workers and 351 controls were recruited at garri factories in Ogbomoso, Nigeria by multistage random sampling technique. Lung functional abnormalities were defined according to standardised European Respiratory Society/American Thoracic Society guidelines. Data analysis was performed using the IBM SPSS statistics version 22.0. Results: The mean age of patients was similar to that of controls (41.7 ± 14.9 vs. 41.6 ± 14.7 yearsP = 0.960). Larger proportion (46.2%) of cassava crisps factory workers had abnormal ventilatory function parameters compared to 6.8% in controls (P < 0.001). The mean peak expiratory flow among garri factory workers was significantly lower than that of the controls; 268.25 ± 86.20 versus 349.04 ± 97.21 (L/min) (P < 0.001), likewise the mean forced vital capacity (FVC) (litres) and forced expiratory volume (FEV1) (litres) of garri factory workers and controls were significantly lower than those of the controls; 2.55 ± 1.07 versus 2.87 ± 0.79 (P < 0.001) and 2.00 ± 0.76 versus 2.41 ± 0.83 (P < 0.001) with FEV1/FVC ratio of 0.82 ± 0.16 versus 0.87 ± 0.06 (P < 0.001), respectively. The restrictive pattern of ventilatory functional abnormality was predominant among garri factory workers, 92 (26.2%). Sixty-two (17.7%) and 8 (2.3%) of garri factory workers had an obstructive and mixed pattern of ventilatory function abnormalities, respectively. Conclusion: Garri processing workers had significant ventilatory function impairment. Preventive strategies should be encouraged to reduce occupational hazards associated with garri processing in Nigeria.
Keywords: Garri workers, lung function abnormalities, Nigeria, occupational hazard, spirometry
|How to cite this article:|
Oloyede T, Akintunde AA, Adeniran JA, Tanimowo MO, Fawibe EA, Salami AK. Lung function abnormalities among garri processing workers in Ogbomoso, Nigeria. Niger Postgrad Med J 2018;25:149-55
|How to cite this URL:|
Oloyede T, Akintunde AA, Adeniran JA, Tanimowo MO, Fawibe EA, Salami AK. Lung function abnormalities among garri processing workers in Ogbomoso, Nigeria. Niger Postgrad Med J [serial online] 2018 [cited 2019 Feb 20];25:149-55. Available from: http://www.npmj.org/text.asp?2018/25/3/149/242208
| Introduction|| |
Garri (cassava crisps) is a rich source of carbohydrate produced throughout Nigeria. Nigeria remains the largest producer of cassava worldwide followed by Thailand and Indonesia with a production quota of about 20% of the total global output., The global production of cassava in 2014 was 268 million tons and it is an important food source in the tropics (providing the third-highest carbohydrate yield)., Cassava and cassava products are major staple foods consumed by most households in Nigeria and Garri is the most popular form in which cassava it is consumed. An estimated 70% of all cassava products in Nigeria is processed into cassava crisps (Garri).
Cyanide has been detected at levels of 20–46 mg/m3 in the air near large-scale cassava processing facilities in Nigeria. This may be reduced by fermentation for up to 96 h, soaking and sun drying. Irrespective of entry route: inhalation/percutaneous, hydrogen cyanide is uniformly distributed in the human body into the liver, lungs, blood and brain. Acute cyanide toxicity is associated with diverse respiratory manifestations and even death. However, the effect of chronic/recurrent exposure is less documented aside chest discomfort.
About 10–20,000 L of air is breathed into the lungs on a daily basis by an average adult. Much of this air is contaminated by dust particles (organic and inorganic), noxious gases, fumes or vapor. These contaminants may be from the workplace or the environment in general and predispose individuals to developing various forms of lung diseases either in the immediate post-exposure period or following long-term exposure.
There are five steps involved in the production of garri from cassava:
- Peeling and washing: cassava is first peeled and washed thoroughly
- Grating: the washed cassava is then grated into a mash or pulp as part of the processes aimed at removing cyanide from the product. The graters are loaded with the washed roots while the engine is running and the roots are crushed into a mash. The mashed product is then collected into a clean polythene sack ready for the next stage
- De-watering and fermentation: this is done traditionally by applying weights in form of stones or heavy wooden logs to press the excess water out of the bags of cassava mash, the bags are left to drain and ferment for a few days. This process completes the process of removing cyanide from the cassava mash. The end product of this step is a firm, wet cassava cake
- Sieving and roasting: the firm, wet cake from the step above is sieved into small pieces (grits), and this is followed by the hot frying/roasting of the grits in an open frying tray/pan into the final dry and crispy product
- Bagging and storing: the garri is removed from the frying tray and spread thinly on a raised platform in the open air for it to cool down and dry. Afterwards, the product is further sieved according to the taste of the customer. This is then poured into a sack with appropriate plastic lining, sealed and ready for storage. Garri stored in this condition could be kept for up to a year.
During garri production, workers at different stages may have a variable occupational health hazard. These may include body itching and eye itching at one time or the other. Roasting during garri processing where wood is used as source of fuel exposes the workers to significant concentration of particulate matter and smoke as documented earlier from previous studies and prolonged exposure has a deleterious effect on the respiratory health of the individuals.,,, Sieving stage is not particularly associated with any specific problem probably because garri particles are not fine enough to be respirable even though some ultrafine particles may be inhalable and contribute to the ventilatory functional abnormality.
The air pollution associated with garri processing factories may cause pathological damage to the three different parts of the lung namely: the major bronchi; the terminal bronchioles and the alveoli. With acute exposure, there may be reversible bronchospasm with considerable individual variation. The long-term effects include cilia paralysis, bronchial mucous hypersecretion and mucous gland hypertrophy with increase susceptibility to infection. In the terminal bronchioles, the following effects are produced: loss of normal defences from inflammatory processes, adverse effect on surfactant through diminished expression, goblet cell metaplasia, inflammation and obliteration with the resultant premature closure of airways. Ultrafine particles and gases with a high probability of reaching the smallest airways result in increased cells and macrophage aggregation in the alveoli., Despite the abundance of cassava crisp factories in Nigeria, there is little information about the occupational hazard and attendant lung function abnormalities associated with exposures in these factories in Nigeria. The aim of this study was to describe the ventilatory functional abnormalities among workers in garri processing factories in Ogbomoso, Nigeria.
| Methods|| |
The study population comprises garri processing workers in the three out of five randomly selected local government areas in Ogbomoso, Nigeria. The study was done between November 2015 and March 2016. There are 21 factories identified in the study area with a total population of about 7085 workers. Job description of workers include: peelers, grinders/fermentation workers, roasters/fryers and sievers. It was a cross-sectional study. Approval of the Ethical Committee of LAUTECH Teaching Hospital, was obtained before proceeding with the study. The protocol number with the ethics committee is LTH/OGB/EC/2014/044 with the date of ethical approval being October 16, 2014. The heads of each factory and communities were consulted and verbal approval was obtained. An informed consent was also obtained from each participant after thorough discussion session in their best-understood language (English or Yoruba).
Sample size determination
Using Leslie Fisher's formula for population <10,000
nf = n / (1+n/N)where,
nf = sample size for population <10,000
n = sample size for population >10,000
N = estimated study population
Calculating 'n' using n = z2pq/d2 where
z = standard normal deviation = 1.96
p = prevalence of research objective from previous study  = 0.32 (32%)
q = 1 − P = 0.68
d = degree of error = 0.05 (5%).
Hence, n = (1.96)2× (0.32) (0.68)/(0.05)2
n = 334.4
Therefore, nf = 334.4/(1 + 334.4/7085)
nf = 334.4/1.047
nf = 319.39 ≈ 319
Addition of 10% to cater for non-responders, =31.9 ≈ 32
i.e., 319 + 32 = 351
The sample size was calculated as 351 workers. An equal number of controls were recruited from residential areas of Ogbomoso, Nigeria where there were no garri processing factories. The inclusion criteria included those who were willing to participate and who gave informed consent and who had been in the active employment of the garri processing factory for at least 1 year. Those with pre-existing diseases such as chronic obstructive pulmonary disease, asthma or history of heart diseases or smoking were excluded from the study. Four factories were randomly selected from each of the local government making 12 and 29 participants were recruited by random sampling (balloting technique) while additional two were included from the largest of the factory to make up the sample size.
A modified semi-structured questionnaire of the British Medical Research Council (MRC) which has been validated for epidemiological studies was used to obtain information from the participants; namely, sociodemographic characteristics, occupational history, respiratory symptoms and medical history. The following measurements were obtained: height (in meters), weight (in kilogram and body mass index was derived. The waist circumference and blood pressure were also obtained. A standard range peak flow metre (mini-Wright) was used to measure the participants' peak flow in litres per minutes (L/min). This was taken in standing position after proper instruction and practical demonstration. The highest value or the best of at least three readings was recorded for the participant as the maximal expiratory peak flow rate. Three acceptable readings were obtained after at least 3 min of rest.
A standard field spirometer (Spirobank MIR Model number: EQ00748), an equipment by Celki International Limited, Hong Kong was used following the American Thoracic Society/European Respiratory Society guidelines on spirometry. It is auto-calibrating equipment and is not affected by ambient air temperature or pressure. The spirometer was calibrated with 3 L syringe at the Ladoke Akintola University of Technology Teaching Hospital Teaching Hospital, Ogbomoso pulmonary function laboratory. The researcher used himself for biological calibration on a daily basis and after every 10 spirometric readings to ensure the accuracy of the test results. Single-use disposable mouthpiece was used for each participant. Each participant was given detailed instruction with practical demonstration to ensure correct techniques were reproducible. Each participant was allowed to have some practice attempts before readings were taken. 3 min rest was observed in between manoeuvres. The following parameters were recorded: Forced expiratory volume (FEV1) in Litres, forced vital capacity (FVC) in Litres and FEV1/FVC ratio. Individual spirogram were 'acceptable' if they were free from artefacts, had a good start and show satisfactory exhalation with duration of at least 6 s or a plateau in the volume-time-curve or if the subject cannot or should not continue to exhale. Repeatability criteria were also used to assess variability between different readings wherein the two largest values of FVC and FEV1 must be within 0.150 L of each other. These were recorded automatically by the spirometer and the results that met the acceptability and reproducibility criteria were later selected and printed out.
Spirometry indicated the presence of abnormalities if any of the following are recorded:
- FEV1 <80% predicted normal
- FVC <80% predicted normal
- FEV1/FVC ratio <0.7.
The obstructive disorder was defined as FEV1 reduced (<80% of predicted normal) with FVC usually reduced but to a lesser extent and reduced FEV1/FVC ratio <0.7. The restrictive disorder was defined as reduced FEV1 (<80% predicted normal), reduced FVC (<80% predicted normal) with normal FEV1/FVC ratio >0.7. Mixed pattern of disease was defined as reduced FVC <80% of predicted normal and reduced FEV1/FVC <0.7.
Data were analyzed using the IBM SPSS statistics version 22.0. Both univariate and bivariate analysis were performed. Univariate analysis was carried out to explore the data using frequencies and proportions for categorical data and means with standard deviations to summarise quantitative variables (such as height, lung function parameters and particulate matters count). Bivariate analysis was carried out using Chi-square tests to compare categorical variables and independent Student's t-test to compare means between categories of binary variables. Risk estimation for the outcome of each of the pulmonary function tests and presence of respiratory symptoms was calculated using odds ratio for 2 × 2 contingency table. Bivariate Pearson correlation analysis was also used to determine the relationship between continuous variable. The level of statistical significance was set as P < 0.05.
| Results|| |
[Table 1] shows the sociodemographic profile of the study participants. The mean age of the garri factory workers was comparable to that of the control group (41.7 ± 14.9 vs 41.6 ± 14.9 years, t = 0.580, P = 0.960). Larger proportion of the garri factory workers (32.5%) and controls (31.1%) were within the age range 30–44 years; however, there was no statistically significant difference in the proportion of distribution in the different age groups (P = 0.858). Majority of the participants in the study group and control group were female (90.6%-garri factory workers and 90.0%-controls) with male-to-female ratio of 1.0:9.6 and 1.0:9.0 for garri factory workers and the controls, respectively, no significant statistical difference in the distribution across the two groups (P = 0.899). Larger proportion were Christian (83.2%-garri factory workers and 76.4%-controls) with the significant statistical difference in the distribution within the two groups (P = 0.024). Marital status was significantly different in distribution across the two groups (P = 0.006). Majority (70.1%-garri factory workers and 72.9%-controls) were married. Larger proportion (34.8%-garri factory workers and 29.9%-control) were educated up to the secondary school level. There was no significant difference in the mean height of participants (P = 0.12).
|Table 1: Socio-demographic profile of the participants within the study groups|
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[Table 2] shows a pattern of ventilatory function parameters within the study and control groups. About 46% of garri factory workers have abnormal ventilatory function parameters compared with the controls (6.8%), (P < 0.001) with the garri factory workers about 17 times more likely to have abnormal ventilatory function compared with controls as shown in the table (odds ratio = 17.002, confidence interval = 10.014–32.065; P < 0.001). [Table 3] shows lung function parameters of participants within the study group and controls.
|Table 2: Pattern of ventilatory function parameters within the study group and controls|
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|Table 3: Spirometry parameters of participants within the study group and controls|
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The mean peak expiratory flow (PEF) in garri factory workers was 268.25 ± 86.20 L/min was significantly lower than that of controls 349.04 ± 97.21, (P < 0.001). The mean forced vital capacity, forced expiratory volume in 1 s and forced expiratory volume in one second/forced vital capacity ratio were also significantly lower in garri factory workers (P < 0.001). [Table 4] shows types of different spirometric abnormalities within the study group and controls. Restrictive lung disease was statistically higher in garri factory workers (26.2%) compared with the controls (2.3%) P < 0.001. Obstructive lung disease and mixed lung disease were also statistically significantly higher in prevalence in garri factory workers than in controls (P < 0.001).
[Table 5] shows the results of a bivariate correlation of spirometric abnormality with duration of the occupation, hours of work per day and the presence of respiratory symptoms among garri factory workers. A weak correlation was found between spirometric abnormality and presence of respiratory symptoms (P = 0.041). However, no statistically significant correlations were found between abnormal spirometric parameters and occupational history (duration of occupation and hours of work per day). [Table 6] shows the relationship between ventilatory function parameters and stages of garri production participant is involved in. There was no statistically significant relationship between ventilatory function parameters and stages of garri processing (peeling stage, grinding stage, the frying stage and sieving stage) (P > 0.05).
|Table 5: Correlation of spirometric abnormality with duration of occupation, hours of work per day in garri factory workers|
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|Table 6: Relationship between ventilatory function parameters and stages of garri production participant was involved in|
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| Discussion|| |
It is well established, that wood fire and other biomass sources of fuel emit significant quantities of known health-damaging air pollutants with an attendant increase in the frequency of respiratory symptoms and declining lung function in the population exposed.,,, In this study, the respiratory symptoms and ventilatory functions of the garri processing factory workers in Ogbomoso, Nigeria were assessed and compared with apparently healthy controls.
The prevalence of respiratory symptoms was higher among the study population as compared with the controls. One hundred and sixty-two (46.2%) of the garri workers had an abnormal pulmonary function based on spirometry and the prevalence of ventilatory function abnormalities were 26.2%, 17.7% and 2.3% for restrictive, obstructive and mixed lung diseases, respectively.
The mean age of the garri workers (41.7 ± 14.9) and that of the control groups (41.6 ± 14.9) is higher than the mean age found in some similar studies in different parts of Nigeria such as among Maisuya in Kebbi state  (30.44 ± 6.7 years), and among dwellers of fishing settlement in Niger Delta region  (31.46 ± 13.03 years). Age is an important determinant of lung function parameters as some ventilatory abnormalities are more common with advanced age. However, the mean age was in tandem with a study by Peter et al. who found an average of 40+ years among some Nigerian men and women chronically exposed to fish drying using burning firewood.
In agreement with the higher prevalence of respiratory symptoms of 48.4% among the study group, a larger proportion, 46.2% of the study group had abnormal lung function parameters while only 6.8% had abnormal spirometry among the controls. The study found a significant difference in all the spirometry parameters between the garri workers and the controls. This finding is comparable to the work of Perez-Padilla et al. in Mexican women exposed to biomass smoke, Adewole et al. amongst Maisuya in Kebbi State, Nigeria and Assad et al. also among Mexican women. The mean PEF in garri workers was significantly lower than that of the controls. There were similar statistically significant lower FEV1, FVC and FEV1/FVC values in garri workers compared with the controls. This could be due to the long-term effect of occupational exposure to dust and garri particles among the garri processing factory workers. We assume this could be due to the additive effect of occupational exposure and domestic exposure to other biomass. Similarly, extra-occupational exposure such as passive cigarette smoking, vehicular smoke and domestic pollution from burning of biomass fuel are confounding variables that could have contributed to the additive effect on the respiratory function of garri processing factory workers in this study., The statistically significant reduction in all parameters of lung functional abnormalities as shown in this study may be related to progressive lung injury due to inhalation of dust and garri particles in the course of the various stage of processing of cassava flakes. Because there is no definite demarcation both in boundary and duty schedules in most of the stages of cassava processing, there appears to be a uniform impact on the respiratory function of the study participants as reported in this study. This trend in spirometry parameters is consistent with the findings of previous workers among various populations exposed to biomass fuel aside from the occupational exposure.,,,
The prevalence of abnormal ventilatory function among garri workers was significantly higher when compared with that of controls, this finding is similar to the findings of Desalu et al. Restrictive pattern of ventilatory function was predominant among garri workers with a prevalence in more than a quarter of them. The restrictive, obstructive and mixed pattern of functional ventilatory abnormalities were also present in the study population in different proportions. It is however at variance with the findings of Umoh et al. among fishers in Niger Delta where obstructive ventilatory defect predominated followed by restrictive ventilatory defect and the mixed pattern. In their work, cigarette smokers were not excluded which could have contributed to their finding of higher prevalence of obstructive lung disease. Furthermore, majority of their study population were in their late fourth and fifth decade of life during which the prevalence of obstructive lung disease increases. No relationship existed between obstructive ventilatory defect and stages of garri production. However, there was a significant relationship between sieving as a stage of production and ventilatory function defect (restrictive and mixed patterns). The reason for this association is probably that garri particles may be inhalable in addition to the effect of smoke from biomass burning generally.
| Conclusion|| |
Ventilatory function parameters of PEF, FEV1, FVC and FEV1/FVC ratio were significantly lower among garri workers compared to the control population. Exposure to other biomass aside workplace was also found to be significantly associated with increased respiratory symptoms and ventilatory function abnormality. Restrictive ventilatory function defects, followed by obstructive defects were the main abnormality found in the study group. Garri production process therefore predisposed workers to increased respiratory symptoms and abnormal spirometry. We recommend the use of dust respirators, breathing apparatus and cleaner source of energy like liquefied petroleum gas while at work to mitigate the ventilatory abnormalities associated with garri processing factories. We also recommend periodic health assessment regarding lung function test to be carried out yearly on the workers to detect early abnormalities and any worker whose health has already been affected by the air pollution to be referred for appropriate intervention.
The medical interns and research assistants in the department of Medicine, LAUTECH Teaching Hospital, Ogbomoso, Nigeria.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Knipscheer H, Ezedinma C, Kormawa P, Asumugha G, Makinde K, Okechukwu R, et al
. Opportunities in the industrial cassava market in Nigeria. Int Inst Trop Agric 2007;1:2-47.
Echebiri RN, Edaba ME. Production and utilization of cassava in Nigeria: Prospects for food security and infant nutrition. PAT 2008;4:38-52.
Tsegai D, Kormawa PC. Determinants of urban household demand for cassava products in Kaduna, Northern Nigeria: An application of the AIDS model. Eur J Dev Res 2009;21:435-47.
Nwokoro SO, Adegunloye HD, Ikhinmwin AF. Nutritional composition of garri sievates collected from some locations in Southern Nigeria. Pak J Nutr 2005;4:257-61.
Centres for Disease Control and Prevention. The National Institute for Occupational Safety and Health: Hydrogen Cyanide; Systemic Agent. Available from: http://www.cdc.gov/niosh/emergencycard/
. [Last accessed on 2015 Apr 20].
Naeher LP, Brauer M, Lipsett M, Zelikoff JT, Simpson CD, Koenig JQ, et al.
Woodsmoke health effects: A review. Inhal Toxicol 2007;19:67-106.
Tanimowo MO. A Synopsis of Environmental and Occupational Lung Diseases. 1st
ed. Osogbo, Nigeria: Published by ATMAN Ltd; 2006.
Zanobetti A, Schwartz J. The effect of fine and coarse particulate air pollution on mortality: A national analysis. Environ Health Perspect 2009;117:898-903.
Ostro B, Lipsett M, Reynolds P, Goldberg D, Hertz A, Garcia C, et al.
Long-term exposure to constituents of fine particulate air pollution and mortality: Results from the California teachers study. Environ Health Perspect 2010;118:363-9.
Ciencewicki J, Trivedi S, Kleeberger SR. Oxidants and the pathogenesis of lung diseases. J Allergy Clin Immunol 2008;122:456-68.
Tanimowo MO. Respiratory disease among Nigerians working in a sugar industry. East Afr Med J 1996;73:556-9.
Künzli N, Perez L, Rapp R. Air quality and health. Lausanne: European Respiratory Society; 2010.
Betchley C, Koenig JQ, van Belle G, Checkoway H, Reinhardt T. Pulmonary function and respiratory symptoms in forest fire-fighters. Am J Ind Med 1997;31:503-9.
Adewole OO, Desalu OO, Nwogu KC, Adewole TO, Erhabor GE. Respiratory symptoms and lung function patterns in workers exposed to wood smoke and cooking oil fumes (mai suya) in Nigeria. Ann Med Health Sci Res 2013;3:38-42.
] [Full text]
Erhabor G. Pulmonary Function Tests: Spirometry and Peak Flow in Clinical Practice. 1st
ed. Ile-Ife, Nigeria: Published by Asthma and chest care foundation; 2010. p. 11-32.
Miller MR, Hankinson J, Brusasco V, Burgos F, Casaburi R, Coates A, et al.
Standardisation of spirometry. Eur Respir J 2005;26:319-38.
Boman BC, Forsberg AB, Järvholm BG. Adverse health effects from ambient air pollution in relation to residential wood combustion in modern society. Scand J Work Environ Health 2003;29:251-60.
Desalu OO, Adekoya AO, Ampitan BA. Increased risk of respiratory symptoms and chronic bronchitis in women using biomass fuels in Nigeria. J Bras Pneumol 2010;36:441-6.
Akani AB, Dienye PO, Okonko IB. Respiratory symptoms amongst female in a fishing settlement in Niger Delta, Nigeria. Afr J Prim Health Care Fam Med 2011;3:1-5.
Peters EJ, Esin RA, Immananagha KK, Siziya S, Osim EE. Lung function status of some Nigerian men and women chronically exposed to fish drying using burning firewood. Cent Afr J Med 1999;45:119-24.
Pérez-Padilla R, Regalado J, Vedal S, Paré P, Chapela R, Sansores R, et al.
Exposure to biomass smoke and chronic airway disease in Mexican women. A case-control study. Am J Respir Crit Care Med 1996;154:701-6.
Assad NA, Kapoor V, Sood A. Biomass smoke exposure and chronic lung disease. Curr Opin Pulm Med 2016;22:150-7.
Adam M, Schikowski T, Carsin AE, Cai Y, Jacquemin B, Sanchez M, et al.
Adult lung function and long-term air pollution exposure. ESCAPE: A multicentre cohort study and meta-analysis. Eur Respir J 2015;45:38-50.
Umoh V, Peters E, Erhabor G, Ekpe E, Ibok A. Indoor air pollution and respiratory symptoms among fishermen in the Niger Delta of Nigeria. Afr J Respir Med 2013;9:17-21.
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]