Burden of COPD and lung cancer attributable to household air pollution in Morocco: a secondary analysis using population attributable fractions

Abstract

Objective

To estimate the burden of household air pollution (HAP) on chronic obstructive pulmonary disease (COPD) and lung cancer in Morocco in 2019 using population attributable fractions (PAFs).

Design

Secondary analytical study based on sex-specific PAF estimation combining Moroccan exposure prevalence from a Moroccan population-based survey conducted in 2010–2011, pooled relative risks from an international meta-analysis, national disease frequency estimates (for COPD, two prevalence sources were used: 2010–2011 observed Moroccan data and 2019 modelling-based estimates), 2019 burden indicators and direct medical costs.

Setting

Morocco.

Participants

Adults aged 40 years and older included in the Burden of Obstructive Lung Disease (BOLD I) survey in Fez, Morocco.

Main outcome measures

Sex-specific PAFs, attributable COPD and lung cancer cases, disability-adjusted life years (DALYs) and annual direct medical costs attributable to HAP.

Results

In Morocco, HAP accounted for 14.4% (95% CI 8.4% to 21.6%) of COPD cases in men and 25.3% (95% CI 17.0% to 34.0%) in women, and for 14.2% (95% CI 7.9% to 21.8%) of lung cancer cases in men and 25.0% (95% CI 16.1% to 34.2%) in women. The estimated number of COPD cases attributable to HAP ranged from 661 717 (95% CI 411 046 to 948 444) using modelling-based prevalence estimates to 815 368 (95% CI 509 160 to 1 163 973) using Moroccan BOLD I prevalence estimates, while 1356 (95% CI 775 to 2041) lung cancer cases were attributable to HAP. Total attributable DALYs were estimated at 62 561.2 (95% CI 37 588.4 to 91 439.2). Total annual direct medical costs attributable to HAP ranged from US$529.9 million (95% CI US$328.9 million to US$760.0 million) to US$651.6 million (95% CI US$406.6 million to US$930.6 million), depending on the COPD prevalence source used.

Conclusions

HAP contributes substantially to the respiratory and economic burden in Morocco. These estimates should be interpreted considering the regional source of exposure data and the application of pooled international relative risks to the Moroccan context.

Introduction

Household air pollution (HAP) as defined by the WHO, results from the use of solid fuels such as kerosene, biomass (including wood, animal dung and agricultural waste) and coal for cooking and/or home heating.¹ It is a major public health concern, particularly in low- and middle-income countries (LMICs).²

It is estimated that one-third of the world population—around 2.3 billion people—cook using open fires or inefficient stoves powered by kerosene, biomass and coal.³ In 2020, HAP was linked to an estimated 3.2 million deaths worldwide.¹ Biomass smoke contains many harmful pollutants comparable to those found in tobacco smoke, including fine particulate matter (PM2.5 and PM10), carbon monoxide, polycyclic aromatic hydrocarbons, volatile organic compounds and nitrogen oxides.⁴

Recent findings from the Global Burden of Disease Study 2019 highlight the significant burden of air pollution—including HAP—on public health in North Africa and the Middle East.⁵ The study revealed that fine particulate matter and carbon monoxide from household sources such as biomass burning for cooking and heating contribute substantially to disease burden, mortality and reduced life expectancy in these regions. In fact, life expectancy in North Africa and the Middle East could be shortened by approximately 1.6 years due to the combined effects of ambient and HAP.

STRENGTHS AND LIMITATIONS OF THIS STUDY

• Secondary analysis combined Moroccan exposure data, pooled outcome-specific relative risks, national disease frequency estimates, WHO burden indicators and Moroccan cost data to estimate the burden attributable to household air pollution.

• CIs for population attributable fractions incorporated uncertainty from both exposure prevalence and relative risk estimates.

• Chronic obstructive pulmonary disease burden was estimated using two prevalence sources to partly address temporal uncertainty.

• Direct medical costs were estimated using Moroccan-specific cost data from 2019.

• Exposure data were regional (Fez) rather than nationally representative, and pooled international relative risks were assumed applicable to Morocco.

In Morocco, although precise data on the use of traditional biomass within the energy mix remain limited, estimates suggest that it accounted for approximately 5.2% of primary energy consumption in 2019. This energy source is predominantly used in rural households, particularly for cooking and heating, as well as in the tertiary sector, notably in public baths (‘hammams’) and traditional ovens.⁶ A study conducted in Morocco revealed that 49% of Moroccan women were exposed to biomass smoke, with 48.8% exposed to wood-based fuels and 2.9% to charcoal-based fuels.⁷

HAP, primarily originating from biomass smoke, is a significant risk factor for a wide range of diseases, particularly respiratory disorders,⁸ which often stem from inflammation of the airways, oxidative stress induced by the particles and gases, or changes in the gas exchange processes within the lungs.⁴ According to the WHO estimates, chronic obstructive pulmonary disease (COPD) and lung cancer are among the primary respiratory diseases associated with HAP exposure.¹

It is well established that exposure to HAP is associated with both the development and the exacerbation of COPD,^{2 8 9} which represents a significant global burden of morbidity and mortality, ranking as the fourth leading cause of death worldwide.¹⁰ The number of deaths attributable to COPD increased from 3.23 million in 2019¹¹ to 3.5 million in 2021, accounting for approximately 5% of global deaths that year.¹⁰ This severe respiratory disease is particularly prevalent in LMIC, where approximately 90% of COPD-related deaths among individuals under the age of 70 occur, making COPD the seventh leading contributor to poor health globally, as measured in disability-adjusted life years (DALYs). While smoking is responsible for more than 70% of COPD cases in high-income countries, it accounts for only 30%–40% of cases in LMIC, with HAP being a major risk factor.¹⁰

Similarly, lung cancer remains the leading cause of cancer-related deaths worldwide, with the highest mortality rates observed in both men and women.¹² While smoking is widely recognised as the primary cause—accounting for approximately 85% of all cases,¹²—a well-established association also exists between HAP, particularly from the use of solid fuels, and an increased risk of lung cancer, especially among heavy smokers.¹³

In Morocco, the prevalence of COPD is estimated at 16.6% (95% CI 12.7% to 20.5%) among men and 8.3% (95% CI 6.9% to 9.7%) among women,¹⁴ while lung cancer is the most commonly diagnosed cancer among men, accounting for 26% of all cancer cases recorded between 2013 and 2017.¹⁵ Additionally, approximately 22.9% of the Moroccan population is exposed to wood-burning fuels (23.7% of men and 22.2% of women), while 1.3% are exposed to charcoal-burning fuels (1.4% of men and 1.2% of women). Notably, 46.3% of women are exposed to wood-fired cooking and 2% to charcoal-fired cooking.¹⁶ Assessing the burden specifically attributable to HAP is particularly relevant, because household biomass exposure appears to represent a distinct respiratory risk factor rather than merely a proxy for tobacco smoking or occupational exposures. In a Moroccan population-based study, smoking and occupational dust exposure were considered separately and biomass exposure remained independently associated with COPD after multivariable adjustment.¹⁶

Despite its recognition as a major public health issue worldwide, the specific impact of HAP on morbidity, mortality and healthcare costs related to respiratory diseases in Morocco has not yet been quantified. This study aims to fill this gap by providing precise estimates of the burden attributable to HAP in Morocco—including the calculation of population attributable fraction (PAF), the number of disease cases, DALYs lost and associated economic costs—focusing on its primary health outcomes: COPD and lung cancer.

Methods

Study design and setting

This was a secondary analytical study estimating the 2019 burden of COPD and lung cancer attributable to HAP in Morocco using PAFs. The analysis combined sex-specific HAP exposure prevalence, outcome-specific relative risks (RRs), national estimates of disease frequency, burden indicators and direct medical costs to quantify attributable cases, DALYs, years of life lost (YLLs), years lived with disability (YLDs) and direct medical costs.

The study focused on Morocco in 2019 as the target year for burden estimation. HAP exposure prevalence was derived from the Moroccan arm of the Burden of Obstructive Lung Disease (BOLD I) study conducted in Fez in 2010–2011 and was retained as the exposure source because COPD and lung cancer are chronic outcomes that generally reflect long-term cumulative exposure rather than only contemporaneous exposure.

Data sources

The data sources used in this analysis are described below according to their analytical role: HAP exposure prevalence, pooled RRs, disease frequency estimates, burden indicators and direct medical costs.

Household air pollution exposure data

Exposure to HAP was derived from the Moroccan arm of the BOLD I study, a population-based survey conducted in Fez, Morocco, in 2010–2011 using the standardised BOLD methodology. The study included adults aged 40 years and older and collected data through interviewer-administered questionnaires and standardised spirometry procedures.¹⁷

In Fez, participants were recruited from the Sais district using a two-stage cluster sampling design, in which 10 administrative units were randomly selected from 31 and households were then systematically sampled within each selected unit. The final Moroccan BOLD biomass analysis included 760 participants, comprising 350 men and 410 women. Biomass exposure was assessed through structured face-to-face interviews conducted by trained and certified staff in the participants’ native language and was defined as self-reported use of biomass fuels for cooking and/or heating, including wood, charcoal and kerosene; however, no participant in the Moroccan sample reported kerosene use. Exposure assessment also included the duration of biomass use in years. The BOLD I data showed long exposure durations for the main biomass source, with a mean wood-heating exposure of 20.1±12.9 years in the overall sample, 20.1±13.6 years in men and 13.8±11.4 years in women; among women, the mean duration of wood-cooking exposure was 17.7±11.5 years. However, information on household ventilation during the relevant period of biomass exposure was not available.¹⁸

For the present burden analysis, the sex-specific prevalence estimates of HAP exposure used in the PAF calculations were derived from a secondary analysis of the Moroccan BOLD I dataset and were 24.0% in men and 48.3% in women, with corresponding 95% CIs of 19.5% to 28.5% and 43.5% to 53.1%, respectively.

Although the exposure data were obtained from Fez rather than from a nationally sampled survey, they were retained because they represent the most detailed Moroccan source currently available on household biomass exposure, including fuel type and duration of use. These estimates were derived from a population-based survey using standardised procedures, which supports their validity for use in the present analysis.

Source of relative risks

The RRs used for COPD and lung cancer were obtained from a large international systematic review and random-effects meta-analysis that evaluated the association between HAP and adverse health outcomes. This review included 476 studies from 123 countries, most of them conducted in low- and middle-income settings.⁸

In that review, HAP exposure was defined as the household use of polluting fuels and technologies for cooking or heating, including coal, wood, charcoal, agricultural waste, animal dung and kerosene, compared with no exposure. For the present analysis, we retained the pooled RR estimates for COPD (RR 1.70, 95% CI 1.47 to 1.97) and lung cancer (RR 1.69, 95% CI 1.44 to 1.98), as these outcomes were directly relevant to the respiratory morbidity profile associated with household biomass exposure. These pooled estimates were generated using random-effects models, which were appropriate given the substantial between-study heterogeneity reported in the source review (I²=98.4% for COPD and 96.6% for lung cancer).

Risk of bias in the meta-analysis was assessed according to endpoint ascertainment and adjustment for confounding. In addition, sensitivity analyses were conducted after restricting the evidence base to studies at low or moderate risk of bias, to longitudinal studies and to studies using clean fuels as the comparator. For COPD, the pooled RR remained elevated at 1.74 (95% CI 1.43 to 2.11) in low-risk or moderate-risk studies, 1.21 (95% CI 1.12 to 1.31) in longitudinal studies and 1.44 (95% CI 1.18 to 1.75) in studies using clean fuels as the comparator. For lung cancer, the corresponding estimates were 1.74 (95% CI 1.45 to 2.10), 1.39 (95% CI 0.99 to 1.96) and 1.46 (95% CI 1.28 to 1.66), respectively. Taken together, these analyses support the robustness of the direction of association, while indicating that the magnitude of effect varies according to study design, comparator definition and methodological quality.

The use of these pooled RRs in the present Moroccan analysis was considered methodologically acceptable because the exposure definition in the Moroccan BOLD dataset was conceptually aligned with that of the source review. In addition, the source review combined pooled international RRs with country-level exposure prevalence to estimate burden for 183 countries. In that framework, these pooled estimates included North African studies, notably a Moroccan case–control study on lung cancer¹⁹ and a Tunisian cross-sectional study on COPD,²⁰ which supports the contextual relevance of applying these estimates in Morocco. However, the source meta-analysis did not report exposure-distribution data or harmonised exposure-intensity categories in a form that allowed direct quantitative comparison with the Moroccan BOLD I data. Therefore, comparability of exposure could be assessed conceptually, but not formally tested. In addition, the source meta-analysis did not provide extractable subgroup-specific pooled estimates for North Africa; therefore, a North Africa-specific sensitivity analysis could not be performed in the present study.

Disease frequency data

For COPD, the number of cases was estimated by applying sex-specific prevalence estimates to the corresponding male and female Moroccan populations.²¹ Two approaches were used to derive COPD prevalence: the first was based on observed sex-specific prevalence estimates from the Moroccan BOLD I study (2010–2011),¹⁴ and the second relied on sex-specific 2019 prevalence estimates derived from aggregated global data.²²

For lung cancer, sex-specific numbers of cases were obtained from the Global Cancer Observatory (GCO), which compiles the most reliable cancer statistics available for each country.²³ The GCO’s estimates are derived from multiple sources, including GLOBOCAN, Cancer Incidence in Five Continents and the International Incidence of Childhood Cancer,²⁴ and the 2019 estimates for Morocco were used in this study.

Burden data

For burden estimation, the 2019 WHO estimates of DALYs, YLLs and YLDs for COPD and lung cancer in Morocco were used.²⁵ These estimates were available separately for men and women and were used to derive sex-specific burden estimates.

Cost data

For the economic analysis, previously published Moroccan estimates of direct medical costs for COPD and lung cancer were used; both source studies estimated costs over a 1 year time horizon with 2019 as the reference year.^{26 27}

Population attributable fraction calculation

The estimation of the burden of HAP exposure was based on the calculation of the PAF, which represents the proportion of diseases attributable to a specific risk factor. The PAF has long been a key tool in public health, combining relative risk and the prevalence of exposure to estimate the burden of a risk factor. It helps measure the proportion of disease cases that could have been prevented in the absence of exposure.²⁸ Sex-specific population attributable fractions were calculated for each outcome using the standard formula:²⁹

$${\displaystyle {\displaystyle PAF=\frac{P\times (RR-1)}{(P\times (RR-1))+1}}}$$

• P: The sex-specific prevalence of HAP exposure.

• RR: The relative risk measuring the association between exposure to HAP and the development of each disease.

Lower and upper bounds of the PAF were estimated by substituting the lower and upper bounds of the exposure prevalence and RR estimates into the same formula.³⁰

$${\displaystyle {\displaystyle \text{CI of the PAF}=\left[\frac{P_{inf}\times (R{R}_{inf}-1)}{(P_{inf}\times (R{R}_{inf}-1))+1};\frac{P_{sup}\times (R{R}_{sup}-1)}{(P_{sup}\times (R{R}_{sup}-1))+1}\right]}}$$

These sex-specific PAFs were then applied to the corresponding sex-specific estimates of disease cases, DALYs, YLLs and YLDs to quantify the burden attributable to HAP in Morocco in 2019.

Estimation of cases attributable to HAP in Morocco

To estimate the number of cases attributable to HAP in 2019 for each disease, we first estimated the number of cases separately for men and women in Morocco and then multiplied these sex-specific case counts by the corresponding sex-specific PAFs.

DALYs, YLLs and YLDs attributable to HAP

According to the WHO, ‘the burden of disease is calculated using the DALYs, where one DALY represents the loss of the equivalent of one year of full health. DALYs for a disease or health condition are the sum of YLLs due to premature mortality and the YLDs due to prevalent cases of the disease or health condition in a population’.²⁵

The WHO provides national estimates of DALYs, YLLs and YLDs for each country by cause and sex. YLLs are calculated by multiplying the number of deaths from a given disease by a loss function, defined as the difference between a reference life expectancy and the age at death. YLDs are estimated by multiplying the number of incident cases by the average duration of the disease and a severity factor (ranging from 0 for perfect health to 1 for death). These calculations incorporate a 3% time discount rate and age weighting, which assigns less value to years lost at very young and older ages.³¹

To estimate the burden attributable to HAP in Morocco, the 2019 WHO estimates of DALYs, YLLs and YLDs for COPD and lung cancer²⁵ were multiplied by the corresponding sex-specific PAFs.

Direct medical cost attributable to HAP

The annual direct medical costs attributable to HAP in Morocco were calculated by multiplying the number of HAP-attributable cases for each disease by previously published Moroccan estimates of direct medical cost per patient.^{26 27} For both COPD and lung cancer, the cost inputs were based on healthcare resource use in 2019 and were considered over a 1 year time horizon; therefore, 2019 was used as the reference year for the economic analysis, and no additional inflation adjustment was applied. These estimates reflected direct medical costs from a societal perspective, including expenses borne by patients, health insurance and the healthcare system.^{26 27} The estimated costs were US$4455.3 per person for lung cancer,²⁶ US$791.7 per person for COPD stages A and B and US$2080.6 per person for stages C and D.²⁷

Given that medical costs differ considerably between COPD stages A/B and C/D, it was necessary to identify the prevalence of each stage. However, these data were not available. The modelling analysis²² only reported the overall prevalence of COPD, without providing a breakdown by disease stage. Similarly, the BOLD I study,¹⁴ although conducted on the Moroccan population, did not report the prevalence of stages B, C and D separately. This methodological choice was due to the extremely low frequency of stages C and D, which led the authors to present only the overall COPD prevalence and the prevalence of stage B and above. Moreover, given the substantial difference in medical costs between early (A and B) and advanced (C and D) stages, using the higher cost estimates could have led to an overestimation of the total economic burden. To ensure a more conservative and realistic estimate, we therefore used the cost estimates associated with the early stages of the disease.

Total annual direct medical costs attributable to HAP were calculated separately for COPD and lung cancer by multiplying the disease-specific number of HAP-attributable cases by the corresponding annual direct medical cost per patient. For COPD, cost estimates were calculated using attributable case counts derived from both the Moroccan BOLD I prevalence estimates and the modelling analysis. For lung cancer, cost estimates were calculated using the corresponding number of HAP-attributable lung cancer cases. Total annual direct medical costs attributable to HAP were obtained by summing the attributable costs for COPD and lung cancer.

Statistical analysis

All analyses were conducted separately for men and women. For COPD, sex-specific case numbers in Morocco in 2019 were estimated by multiplying sex-specific prevalence estimates by the corresponding male and female population counts. Sex-specific COPD cases attributable to HAP were then estimated by multiplying these case numbers by the corresponding sex-specific PAFs.

For lung cancer, sex-specific case numbers in Morocco in 2019 were obtained from the GCO, and sex-specific cases attributable to HAP were estimated by multiplying these case numbers by the corresponding sex-specific PAFs.

Sex-specific DALYs, YLLs and YLDs attributable to HAP were estimated by multiplying the 2019 corresponding sex-specific WHO burden estimates for Morocco for COPD and lung cancer by the relevant sex-specific PAFs. Total attributable DALYs were then calculated by summing the sex-specific attributable DALY estimates for COPD and lung cancer.

For the economic analysis, disease-specific direct medical costs attributable to HAP were estimated by multiplying the number of HAP-attributable cases by the corresponding annual direct medical cost per patient. Total annual direct medical costs attributable to HAP were obtained by summing the attributable costs for COPD and lung cancer.

A online supplemental appendix provides the analytical formulae, input parameters and step-by-step calculation procedure used to derive the sex-specific and total estimates.

Access to data

The authors had access to aggregated burden and cost data from published or publicly available sources and to previously collected Moroccan BOLD I data used to derive sex-specific HAP exposure prevalence estimates. The research team had authorised access to the Moroccan BOLD I dataset, which had been collected previously in Fez, Morocco. The present analysis was based exclusively on secondary data and did not involve new data collection.

Patient and public involvement statement

Patients and/or the public were not involved in the design, conduct, reporting or dissemination plans of this secondary analysis.

Results

Table 1 illustrates the impact of HAP on COPD morbidity in Morocco for the year 2019. It shows that the fraction of morbidity attributable to HAP was 14.4% (95% CI 8.4% to 21.6%) in men and 25.3% (95% CI 17.0% to 34.0%) in women. Depending on the prevalence source used, the total number of COPD cases attributable to HAP was estimated at 661 717 (95% CI 411 046 to 948 444) using the modelling analysis and 815 368 (95% CI 509 160 to 1 163 973) using the BOLD I study estimates.

Table 1. Attributable morbidity to HAP in Moroccan patients with COPD in 2019.

		Morbidity
		Men	Women
RR (95% CI)8		1.70 (1.47 to 1.97)	1.70 (1.47 to 1.97)
Proportion of the Moroccan population exposed to HAP (95% CI)		24.0% (19.5% to 28.5%)	48.3% (43.5% to 53.1%)
PAF (95% CI)		14.4% (8.4% to 21.6%)	25.3% (17.0% to 34.0%)
Prevalence of disease	According to the modelling analysis22	14.4%	6.2%
	According to the BOLD I study14	16.6%	8.3%
Moroccan population21		18 280 000	18 020 000
Number of cases (Prevalence of disease × Moroccan population)	According to the modelling analysis22	2 632 320	1 117 240
	According to the BOLD I study14	3 034 480	1 495 660
HAP-related cases (95% CI) (Number of cases × PAF)	According to the modelling analysis22	379 055 (221 115 to 568 582)	282 662 (189 931 to 379 862)
		661 717* (411 046 to 948 444)
	According to the BOLD I study14	436 966 (254 897 to 655 448)	378 402 (254 263 to 508 525)
		815 368* (509 160 to 1 163 973)

^*Total of HAP-related cases (95% CI).

BOLD, Burden of Obstructive Lung Disease; COPD, chronic obstructive pulmonary disease; HAP, household air pollution; PAF, population attributable fraction; RR, relative risk.

Table 2 presents the attributable morbidity for lung cancer. The PAF was 14.2% (95% CI 7.9% to 21.8%) in men and 25.0% (95% CI 16.1% to 34.2%) in women, corresponding to a total of 1356 (95% CI 775 to 2041) lung cancer cases attributable to HAP in 2019.

Table 2. Attributable morbidity to HAP in Moroccan patients with lung cancer in 2019.

	Morbidity
	Men	Women
RR (95% CI)8	1.69 (1.44 to 1.98)	1.69 (1.44 to 1.98)
Proportion of the Moroccan population exposed to household air pollution (95% CI)	24.0% (19.5% to 28.5%)	48.3% (43.5% to 53.1%)
PAF (95% CI)	14.2% (7.9% to 21.8%)	25.0% (16.1% to 34.2%)
Number of cases23	7884	941
HAP-related cases (95% CI) (Number of cases × PAF)	1 120 (623 to 1719)	236 (152 to 322)
	1356* (775 to 2041)

^*Total of HAP-related cases (95% CI).

HAP, household air pollution; PAF, population attributable fraction; RR, relative risk.

As shown in table 3, the burden attributable to HAP was dominated by YLLs rather than YLDs for both COPD and lung cancer. Total DALYs attributable to HAP were estimated at 62 561.2 (95% CI 37 588.4 to 91 439.2), with a greater contribution from lung cancer in men and from COPD in women.

Table 3. YLLs, YLDs and DALYs attributable to HAP in Morocco in 2019.

	COPD		Lung cancer
	Men	Women	Men	Women
YLLs25	67 200	44 900	193 200	21 200
YLDs25	20 200	22 700	800	100
DALYs25	87 300	67 600	194 100	21 300
PAF (95% CI)	14.4% (8.4% to 21.6%)	25.3% (17.0% to 34.0%)	14.2% (7.9% to 21.8%)	25.0% (16.1% to 34.2%)
YLLs (95% CI) attributable to HAP YLLs × PAF	9676.8 (5644.8 to 14 515.2)	11 359.7 (7633 to 15 266)	27 434.4 (15 262.8 to 42 117.6)	5300 (3413.2 to 7250.4)
YLDs (95% CI) attributable to HAP YLDs × PAF	2908.8 (1696.8 to 4363.2)	5743.1 (3859 to 7718)	113.6 (63.2 to 174.4)	25 (16.1 to 34.2)
DALYs (95% CI) attributable to HAP DALYs × PAF	12 571.2 (7333.2 to 18 856.8)	17 102.8 (11 492 to 22 984)	27 562.2 (15 333.9 to 42 313.8)	5325 (3429.3 to 7284.6)
Total DALYs (95% CI) attributable to HAP	62 561.2 (37 588.4 to 91 439.2)

COPD, chronic obstructive pulmonary disease; DALYs, disability-adjusted life years; HAP, household air pollution; PAF, population attributable fraction; YLDs, years lived with disability; YLLs, years of life lost.

Table 4 shows that the direct medical costs attributable to HAP were substantial, particularly for COPD. The annual cost attributable to HAP-related COPD was estimated at approximately US$645.5 million (95% CI US$403.1 million to US$921.5 million) using the BOLD I-based estimates and US$523.9 million (95% CI US$325.4 million to US$750.9 million) using the modelling-based estimates, compared with US$6.0 million (95% CI US$3.4 million to US$9.1 million) for lung cancer. Overall, the total annual direct medical cost attributable to HAP for COPD and lung cancer combined was estimated at approximately US$651.6 million (95% CI US$406.6 million to US$930.6 million) using the BOLD I-based COPD estimates and US$529.9 million (95% CI US$328.9 million to US$760.0 million) using the modelling-based COPD estimates.

Table 4. Annual direct medical cost of COPD and lung cancer attributable to HAP in Morocco in 2019.

	COPD		Lung cancer
	According to the BOLD I study	According to the modelling analysis
HAP-related cases (95% CI)	815 368 (509 160 to 1 163 973)	661 717 (411 046 to 948 444)	1356 (775 to 2041)
Direct medical cost per person per year (US$)	791.7 27		4455.3 26
Annual direct medical cost attributable to HAP (US$) HAP-related cases(95% CI) × direct medical cost per person per year	645 526 845.6 (403 101 972.0 to 921 517 424.1)	523 881 348.9 (325 425 118.2 to 750 883 114.8)	6 041 386.8 (3 452 857.5 to 9 093 267.3)
Total annual direct medical cost attributable to HAP ($) HAP attributable cost of COPD (95% CI) + HAP attributable cost of lung cancer (95% CI)	According to the BOLD I study	651 568 232.4 (406 554 829.5 to 930 610 691.4)
	According to the modelling analysis	529 922 735.7 (328 877 975.7 to 759 976 382.1)

BOLD, Burden of Obstructive Lung Disease; COPD, chronic obstructive pulmonary disease; HAP, household air pollution; PAF, population attributable fraction.

Discussion

To our knowledge, this is the first study to estimate the PAF of HAP in relation to the risk of COPD and lung cancer in Morocco, using Moroccan exposure data derived from a population-based survey conducted in Fez and RRs derived from a large multinational meta-analysis.

HAP is linked to harmful pollutants emitted from commonly used fuels, particularly fine PM2.5, which can deeply penetrate the lungs and enter the bloodstream. These fine particles pose a significant public health threat, affecting not only indoor air quality but also contributing to ambient outdoor air pollution. Indeed, one study estimated that PM2.5 emissions from domestic fuel combustion account for up to 12% of overall PM2.5 exposure in ambient air.³²

In poorly ventilated homes, indoor smoke can contain concentrations of fine particles up to 100 times higher than acceptable levels.³³ These fine particles are particularly hazardous to lung tissue. The mechanisms of lung damage caused by these particles include their direct cytotoxicity, the increase in the number of inflammatory cells in the airways and the elevation of inflammatory markers.^{34 35} Furthermore, oxidative stress, induced by the presence of metals in the particles, appears to play a central role in the lung damage they cause.³⁶

COPD and lung cancer are among the diseases most strongly associated with HAP exposure. Our findings confirm this observation in the Moroccan context, showing that HAP appears to be a substantial contributor to the burden of both conditions. Nearly 14% of men and one-quarter of women cases of these respiratory diseases were attributable to HAP. The higher PAF observed in women is mainly explained by greater exposure to HAP, which results from the use of solid fuels for cooking during household chores. Indeed, women are often more exposed because they generally spend more time indoors and are primarily responsible for these tasks whether in Morocco⁷ and globally.^{9 33}

In India, the PAF of HAP in the occurrence of COPD was estimated at 27.5% (95% CI 17.6% to 37.9%).⁸ This value is very close to the PAF of 25.3% (95% CI 17.0% to 34.0%) observed among Moroccan women. Since both estimates were calculated using the same RR, this similarity is likely due to the comparable prevalence of exposure to HAP; 48.3% among Moroccan women and 55% in India.⁸

The results of this study estimate that 62 561.2 DALYs (95% CI 37 588.4 to 91 439.2) were attributable to HAP in Morocco. In comparison, the WHO estimates that DALYs due to all HAP-related diseases in the country amount to 65 801 (95% CI 0 to 251 232).³⁷ However, this comparison should be interpreted cautiously, because the HAP exposure prevalence used in our analysis was derived from a population-based survey conducted in Fez rather than from a nationally representative exposure survey. Although the WHO estimate encompasses all pathologies linked to HAP, while our study focuses specifically on chronic respiratory diseases, the two estimates remain remarkably close. This proximity may be explained by the fact that HAP more frequently affects the respiratory system than other organ systems. Therefore, even though the WHO estimate includes a broader range of HAP-related diseases, it is likely dominated by the burden of respiratory conditions, particularly COPD and lung cancer. Moreover, the similarity between the two estimates can be partially attributed to the wide CI of the WHO estimate, which not only encompasses the CI of our estimate but also reflects a higher degree of uncertainty, making it less precise.

Our findings suggest that respiratory diseases represent a substantial component of the HAP-related burden in Morocco. This interpretation is consistent with the results of a large meta-analysis,⁸ which estimated that HAP accounts for 60.9 million DALYs globally (95% CI 34.6 million to 93.3 million), of which 45.7 million (75%) were due to respiratory diseases. Among these, chronic respiratory diseases (including asthma and COPD) accounted for 18.4 million DALYs, while lung cancer contributed 5.5 million DALYs.

This study also assessed the economic impact of HAP. The findings showed that although the direct medical cost per patient was 5.6 times higher for lung cancer than for COPD, the total cost attributable to HAP in 2019 was nearly 100 times higher for COPD. This striking difference is primarily due to the large disparity in the number of attributable cases; over 600 000 for COPD versus only 1356 for lung cancer.

Our results showed that, in 2019, the total direct medical cost attributable to HAP for COPD and lung cancer was estimated at US$651 568 232.4 (95% CI US$406 554 829.5 to US$930 610 691.4) based on the BOLD I study and US$529 922 735.7 (95% CI US$328 877 975.7 to US$759 976 382.1) according to the modelling analysis. Considering that Morocco’s gross domestic product (GDP) in 2019 was estimated at 1137.3 billion dirhams³⁸ (equivalent to US$119.609 billion), using an exchange rate of 9.5640 dirhams per US dollar,³⁹ the direct medical costs attributable to HAP represented a substantial share of the national economy. Specifically, these costs accounted for 0.54% (95% CI 0.34% to 0.78%) of GDP according to the BOLD I study and 0.44% (95% CI 0.27% to 0.64%) according to the modelling analysis.

This study presents several important strengths in understanding the impact of HAP in Morocco. First, it is pioneering in estimating the burden attributable to HAP in relation to COPD and lung cancer in Morocco, using Moroccan exposure data and population attributable fractions. Second, the prevalence of exposure used in this study dates back to 2010–2011, which is sufficiently distant to be considered a potential cause of the health effects observed in 2019. Third, two approaches were used to estimate the prevalence of COPD in this study. The first was based on the Moroccan BOLD I study conducted in the Fez region, which included apparently healthy adults who underwent spirometric measurements to diagnose COPD.¹⁴ However, this approach raises an important question regarding the relationship between exposure and COPD prevalence: the effects of exposure generally take several years to manifest as COPD, while data on exposure and disease were collected simultaneously. For this reason, we also incorporated a more recent estimate of COPD prevalence in Morocco, derived from a modelling study that compiled data from 162 articles on population surveys conducted at 260 sites across 65 countries.²² Fourth, the RRs used in our estimates were derived from a large international meta-analysis, were adjusted for key confounding factors and showed generally consistent directions of association across sensitivity analyses. Additionally, we calculated CIs for the PAF estimates, helping to account for statistical uncertainty and providing a more robust estimate of the impact of HAP. Fifth, the study highlights the economic cost attributable to HAP, quantifying its impact on Moroccan GDP, which allows us to better target and strengthen preventive interventions. Sixth, this study also calculated the DALYs attributable to HAP in Morocco, a measure that accounts for both premature mortality and morbidity, offering a more comprehensive assessment than simple mortality measures, which are limited to the number of deaths.

However, the study has some limitations. One limitation is its focus primarily on the respiratory consequences of HAP, without exploring other health impacts, which likely underestimates the overall effect of this exposure on public health. Another limitation is that the exposure prevalence used in the analysis was derived from a population-based survey conducted in Fez rather than from a nationally representative exposure survey, and therefore the national interpretation of the attributable-burden estimates should be made cautiously. In addition, information on household ventilation during the relevant period of biomass exposure was not available, preventing us from accounting for this factor in the present analysis. Moreover, although the study accounts for the direct medical costs of HAP, it does not consider indirect costs, such as lost productivity and absenteeism. The omission of indirect costs is mainly due to the lack of available data, which limits the scope of the overall economic analysis of the impact of HAP. Another limitation concerns the estimation of the cost attributable to HAP for patients with COPD. We chose to use the cost estimate for stages A and B, which may underestimate this cost, as the costs for stages C and D are much higher. This choice was motivated by the absence of detailed national data on COPD stage distribution and by the very low prevalence of stages C and D. It was intended as a conservative approach to avoid overestimating the total cost. A further limitation is that, although alternative methodological approaches such as longitudinal cohort designs and additional sensitivity or modelling analyses would be informative, they remain constrained by data availability. A cohort approach would require prospective Moroccan data with sufficient follow-up to capture the latency between HAP exposure and the development of COPD or lung cancer, while additional sensitivity or modelling analyses would require alternative national estimates for key input parameters. This was only partly possible for COPD, for which we used both measured Moroccan prevalence data and a more recent 2019 modelling estimate.

Conclusion

This study highlights the significant impact of HAP on COPD and lung cancer in Morocco, underscoring the urgent need for public health interventions. The promotion of clean cooking solutions, broader access to non-polluting fuels and improved household ventilation should be prioritised, supported by appropriate building standards. Awareness campaigns, particularly targeting women, the most exposed group, as well as the integration of HAP into national strategies for respiratory disease prevention, are also essential. Finally, establishing a system to monitor indoor air quality and conducting prospective and interventional studies will help guide policy decisions based on robust scientific evidence.

Data availability statement

All data relevant to the study are included in the article or uploaded as supplementary information.