Improved stove interventions to reduce household air pollution in low and middle income countries: a descriptive systematic review

We examined the effect of stove interventions as reported by study authors. The majority of authors reported a positive reduction of HAP after the installation of an improved stove. Primarily, the main pollutants measured were carbon monoxide (CO) and particular matter (PM). The time frames of measuring pollutant concentration differed greatly across each study from hourly to seven-day measurements. A meta-analysis of the results was not possible due the disparity between pollutant types, methods, and timing of measurement. While pollutant reductions were reported, frequently, these reductions were not enough to meet WHO air quality recommendations. The study by Hanna et. al. (2012) which has the longest follow-up (4 years) showed no improvement post one year. Beltramo et al’s. [15] solar oven intervention group was higher than the control group (8.09 ppm/h compared to 6.50 ppm/h respectively). The authors reported this unexpected increase in CO exposure was largely due to smaller household size in the intervention group.

A wide range of health outcomes were reported across the studies. Self-report measures within studies reported a reduction of respiratory (e.g. cough, phlegm, wheeze, chest tightness) [16, 17], non-respiratory (e.g. eye discomfort, headache, backache) [18, 19] and sleep symptoms (e.g. snoring, nasal congestion) [17, 20] in intervention groups. However, objective measures of pulmonary function were less conclusive. The RESPIRE study did not significantly improve women’s lung function or reduce physician-diagnosed pneumonia for children younger than 18 months after 12–18 months of improved stove use [16, 21]. Authors of the RESPIRE study suggest that stove or fuel interventions with lower average emissions than the plancha chimney stove may be required for communities with such high exposure to air pollution [21]. Similarly, Clark et. al. [22] found no evidence of association between stove type and lung function. The RESPIRE study did report a non-statistically significant reduction in low birth weight in the intervention groups [23], evidence of a reduction in blood pressure [24] and reduced occurrence of non-specific ST-segment depression [25] suggesting improved stove interventions may potentially affect cardiovascular health.

The TIDieR checklist was completed for each included study. Extracted information included: brief name of the intervention (Item 1); the rationale and goal (Item 2), the stove type and educational material provided (Item 3); who provided the intervention (Item 4), the mode of delivery (Item 6); where the intervention occurred (Item 7); the intervention schedule (Item 8); whether the intervention was tailored (Item 9) or modified during the course of the study (Item 10); and whether intervention adherence and fidelity was assessed (Item 11 and 12).

A brief description of each study can be seen in Tables 1, 2 and 3. Nine studies (6 RCTs, 3 non-RCTs) were affiliated with the Randomized Exposure Study of Pollution Indoors and Respiratory Effects (RESPIRE) study [16, 18, 19, 21, 23‐27]. This was the first RCT to investigate the health effects from solid fuel use [19]. The study occurred in Guatemala and aimed to assess the impact of improved stoves (planchas) on exposure and health outcomes in a rural population reliant on wood fuel. An additional five RCTs were identified, all of which investigated the impact of improved stoves on either exposure outcomes (n = 2) or both exposure and health outcomes (n = 3). The majority of identified non-RCTs were pre-post studies investigating the impact on exposure-related health outcomes or exposure reduction of various stove types. Some studies also assessed traditional cooking practices and the acceptability of stoves to the local community members.

Across the studies more than 15 different stove types were used. The most commonly reported stove was the plancha (largely due to the RESPIRE study), which is an improved chimney woodstove typically built into the home. Other stoves were portable and delivered to the home (e.g. the Eco-Stove [28]) or provided in multiple pieces and built by the household with provided instructions (e.g. the Juntos National Program [29]). In Hanna et al. [8], households were responsible for providing mud for the stove base, labour and payment of about US$0.75 to pay the mason who assisted in building and maintaining the stove. One study investigated the use of a solar oven stove (the HotPot) [15].

Studies were largely led by University and NGO collaborations. The most wide-spread dissemination of stoves (n = 40,000) was led by the Joint UNDP/ World Bank Energy Sector Management Assistance Program [30]. This program involved training of metalsmith workers, establishment of commercial networks and sensitisation campaigns. Multiple studies recruited bilingual community members or community health workers as field staff. Local brick masons or metalsmiths were frequently used to assist in the building of stoves. Some studies identified community members who used and maintained stoves correctly and employed them as stove inspectors or promoters within communities [8].

Table 4 provides a summary of key components of interventions. The majority of studies focused on stove provision only (including education and training on stove use). Very few studies have combined stove provision with additional interventions to reduce HAP such as improving the living environment (e.g., improved kitchen design and ventilation) or modifying user behaviour (e.g., using pot lids, removing children from cooking area).

Figure 2 shows the distribution of study countries identified in the review. In-keeping with the inclusion criteria, only studies from LMIC were included. Fifteen different study countries were identified across Central and South America, Africa and Asia. Figure 2 groups study countries according to the Global Burden of Disease Regions. The countries are colour-coded to highlight areas of high burden of disease attributable to HAP from solid fuels as per Lim et.al. ^5]. Studies have occurred across a range of settings and locations. Importantly, a range of studies have occurred in South Asia and Sub-Saharan Africa where HAP from solid fuels has the highest disease burden.

Most commonly, studies performed baseline assessments and then provided (or installed) the stove with instructions on stove use. Limited interaction between stove installation and post-intervention follow-up was reported. If stoves were damaged or malfunctioning, participant were often responsible for contacting an appropriate person. Uniquely, the RESPIRE study provided weekly maintenance checks.

Post-intervention follow-up ranged from seven days [31] to four years [8]. In Hanna et. al.’s [8] study no meaningful reduction of HAP was seen beyond the first year. No other studies provided follow-up periods beyond two years.

The majority of large-scale and RCT studies included preliminary questionnaires and needs assessments to determine baseline information and cooking practices. Impressions and observed reactions about the improved stoves were reported to impact upon design and dissemination of some interventions [26, 30]. However, once the intervention was designed, limited tailoring took place across studies. In-built stoves were designed around the house requirements and occasionally adjustments were individualised to each study house [32]. Mostly, however, stove provision was standardised across households and limited adaption took place. In one study, abnormally sized or shaped kitchens were excluded [33].

Many studies reported difficulties with adherence and adoption of stoves. ‘Stacking’, the use of traditional stoves in conjunction with improved stoves, was a frequently reported issue. However, while commonly reported as a potential issue, few studies (6/36) actively measured and reported adherence or fidelity data. One study objectively measured stove use with the Stove Use Monitoring System (SUMS) [34] which is fixed to the stove and records the temperature profile over time. Random spot checks by Rosa et. al. [35] and Romieu et. al. [36] reported 64.1 % and 50 % of checked households to be exclusively using the improved stoves. Romieu et. al. [36] conducted a predictive model with longitudinal data to assess factors influencing adoption. The authors reported no clear effect of socio-economic status or education level on stove adoption. Importantly, previous use of a similar stove type was a predictor of improved stove adoption and as such, the authors concluded that greater reinforcement and training of stove use is required in future studies [36]. Much higher adoption rates were reported by the Joint UNDP/ World Bank Energy Sector Management Assistance Program in Niger [30]. This program reported that 96 % of consumers in inspected homes were using the stoves properly, 76 % maintaining it correctly and 93 % had decided to replace it when necessary [30]. This large scale program utilised a sensitisation campaign and publicity to inform both women and men about the existence and advantages of the stove as well as create a market demand. Training on stove use was also provided. Additionally, the design of both the campaign and stove were piloted and modified based on contextual needs.

To date, the RESPIRE studies (Fig. 3) have the highest study quality as per the Cochrane Collaboration Risk of Bias Tool. Great variation exists between the additional RCTs (Fig. 4) with no study achieving all of the study criteria.