Effectiveness of interventions to reduce household air pollution from solid biomass fuels and improve maternal and child health outcomes in low- and middle-income countries: a systematic review protocol

Household cooking, heating and lighting with solid biomass fuel (e.g. wood, dung, charcoal, crop residues) [1] is common in low- and middle-income countries (LMICs) [2] worldwide, producing hazardous levels of household air pollution (HAP) (e.g. carbon monoxide (CO) and particulate mMatter (PM)) [3], and exposure to results in significant morbidity and mortality. The greatest burden of HAP exposure is recognised to be among women of child-bearing age [4] and children under 5 years, due to a disproportionate amount of time spent in the house, with women performing or assisting with household duties [5]. Intrauterine, infancy and early childhood are critical periods of organ development when individuals are particularly vulnerable to the harms of HAP exposure [6]. Adverse health events associated with HAP exposure can occur throughout the life course from conception to old age, but specifically during pregnancy, with evidence for increased risk of low birth weight, preterm birth, stillbirth, gestational hypertension, intrauterine growth retardation (IUGR) and perinatal mortality [7]. Early life health events among infants and children under 5 years include increased risks of acute lower respiratory infection (ALRI), asthma, otitis media, impaired neurodevelopment and all-cause mortality [8, 9]. In context, 31.75 per 100,000 acute respiratory infection (ARI) deaths and 11.68 per 100,00 preterm birth deaths were attributable to HAP globally in 2019 [10].

Ultimately, economic development is associated with clean fuel transitions (e.g. to ethanol, liquid petroleum gas (LPG), electricity), which are fuels that have been recognised to reduce HAP levels to below World Health Organization indoor air quality (WHO-IAQ) guideline levels (CO 7 mg/m³ 24-h average, PM_2.5 25 mg/m³ annual average) [11]; however, socio-cultural factors can contribute to fuel/stove stacking and mixing (where traditional fuels/stoves are used alongside the intervention) which may reduce the efficacy of clean fuel policy implementation [12]. Interim interventions, prior to sustained cleaner fuel availability, to mitigate HAP exposure levels within the household setting are broad ranging, including improved cookstoves (ICS) (e.g. rocket stoves, plancha) [13], solar stoves [14], improved biomass fuels (e.g. briquettes, biomass pellets) [13] and behavioural changes (e.g. removal of the child from the cooking area, outdoor cooking, opening windows) [12]. LPG, for example, has the potential to reduce HAP levels below the WHO-IAQ guideline levels; however, not all interventions achieve this [15‐17] or interim targets (PM_2.5 35 mg/m³ annual average) [18] and are therefore typically harm mitigation measures, with some interventions not reducing exposure at all. In addition, there are often multiple barriers [19] to implementation, uptake and sustained use of interventions, such as fuel affordability and accessibility, cultural and social preferences or lack of relevant infrastructure [20]. Previous systematic reviews have detailed the change in HAP levels [13] and health outcomes (low birth weight, preterm birth, perinatal mortality, paediatric ALRI and chronic obstructive pulmonary disease (COPD)) attributed to ICS interventions [21], in addition to systematic reviews investigating a wider range of HAP interventions for specified symptoms (e.g. blood pressure) [22] and general respiratory and non-respiratory health outcomes [17]. However, to the best of our knowledge, there is a paucity of evidence synthesis concerning the overall benefits to maternal and child health outcomes arising as a consequence of household solid biomass fuel interventions.

The objective of the systematic review protocol outlined here is to assess, among pregnant women, infants and children (under 5 years) in LMIC settings, the effectiveness of interventions which aim to reduce household air pollutant emissions due to household solid biomass fuel combustion, compared to usual cooking practices, in terms of health outcomes associated with HAP exposure. In addition, any information regarding measures of sustained uptake of the intervention within the selected studies will be extracted and discussed. The findings will inform future intervention studies and policy changes, by generating knowledge of effectiveness for achieving improved pregnancy, perinatal, infant and under 5 years child health outcomes in resource-poor settings worldwide.

Established systematic review methods will be used. This protocol has been registered on the International Prospective Register of Systematic Reviews (PROSPERO) (ID: CRD42020164998) [23] and is presented in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocol (PRISMA-P) guidelines [24].

Alternatives to standard practices of household biomass fuel use for cooking, heating and lighting are required within LMICs to combat the morbidity and mortality presented by HAP, with implications for maternal and child health and sustainable economic development. National and local policymakers increasingly recognise the need for effective policy changes to mitigate the health burden associated with HAP exposure; however, there is a lack of evidence regarding affordable, effective and culturally acceptable interventions. This may restrict the progress of such changes, notably in countries which lack widespread access to mains electricity or gas for household cooking, heating and lighting, in addition to limits in transferability of effectiveness of interventions from one context to another. Harm mitigation approaches would bridge the gap before there is widespread affordable access to electricity or gas, but the efficacy of such an intervention requires evaluation. Therefore, this proposed review aims to report the contemporary scientific evidence concerning the effectiveness of HAP mitigation interventions to improve maternal and child health, thus identifying existing research gaps and informing future research and impact activities.