Table 1.

Studies showing the association between indoor air pollution and childhood pneumonia

No.	Country	Name/year of study	Setting	Study design	Study period	Primary/secondary data	Age in months	Exposure	Data collected using	Sample size	Outcome parameter	Main result
1	India	Broor et al. (2001)	Peri-urban	Case-control	March 1995–February 1997	Primary	< 60	Solid fuel use	Questionnaire	512	Single disease episode	Cooking with any other type of fuel other than LPG (OR 2.5, 1.51–4.16)
2	India	Sharma et al. (1998)	Peri-urban	Case-control	November 1994–February 1995	Primary	< 12	Fuel used for cooking	Questionnaire	642	Multiple disease episode	Pneumonia was the most common illness in both fuel groups used at home for both wood and kerosene
3	India	Bassani et al. (2010)	Urban/rural	Case-control	February 1998	Secondary	< 48	Solid fuel use	Survey data	616,391	Mortality and single disease episode	Generally, children (0–4 years) with pneumonia had a higher reported solid fuel use compared to children without pneumonia (boys: PR 1.5, 1–2.4; girls: PR 1.9, 1.1–3.3)
4	Nepal	Dhimal et al. (2010)	Peri-urban	Cross-sectional	October 2008–January 2009	Primary and secondary	< 60	Fuel used for cooking	Questionnaire	545,777	Single disease episode	The solid biomass fuel was the primary source of energy for cooking which attributed to about 50% of the burden of pneumonia in children
5	Botswana	Kelly et al. (2015)	Urban/peri-urban	Cohort study	April 2012–April 2014	Primary	< 24	Wood smoke exposure	Questionnaire	284	Single disease episode and mortality	The risk of failure to respond to treatment at 48 h was increased in households that used wood as a cooking fuel (RR 1.44, 95% CI 1.09–1.92, P = 0.01). This effect was observed in undernourished children (P = 0.02)
6	Gambia	Dionisio et al. (2012)	Urban/peri-urban	Case-control	July 2007–January 2011	Primary	< 60	Exposure to CO	CO measurement questionnaire	1181	Single disease episode	There was an increased risk of pneumonia (OR 4.2, 3.1–5.7) in the rainy season compared to the dry season. Households where firewood or charcoal was purchased exposed children 2.0 (1.2–3.2) or 3.8 (2.1–7.1) times more to indoor air pollution compared to households that collected firewood
7	Gambia	Howie et al. (2016)	Urban/peri-urban	Case-control	June 2007-September 2010	Primary	< 60	Exposure to CO	CO measurement questionnaire	1581	Single disease episode	No association was found between CO exposure and childhood pneumonia. However, bed sharing with someone with a cough and severe pneumonia (OR 5.1, 3.2–8.2) and non-severe pneumonia (OR 7.3, 4.1–13.1). Undernutrition was associated with childhood pneumonia (OR 8.7, 4.2–17.8)
8	Indonesia	Shibata et al. (2014)	Urban	Cross-sectional/case-control	June 2011–June 2012	Primary	< 60	Measured PM2.5 and PM10	PM2.5 measurement questionnaire	461	Single disease episode	Hourly sampling showed significant differences in PM2.5 and PM10 concentration between households in which children with pneumonia lived compared with controls
9	Bangladesh	Ram et al. (2014)	Urban	Case-control	March 2009–March 2010	Primary	< 60	Exposure to PM2.5	PM2.5 measurement questionnaire	994	Single disease episode	PM2.5 was not significantly associated with pneumonia. However, crowding, aluminium roofing in living space, households with lower socioeconomic status and being a boy were associated with pneumonia
10	India	Mahalanabis et al. (2002)	Urban/peri-urban	Case-control	December 1997–November 1998	Primary	< 35	Risk factors	Questionnaire	262	Single disease episode	Solid fuel use with OR 3.97, 2–7.88, compared to not using any solid fuel for cooking
11	Nepal	Karki et al. (2014)	Peri-urban and rural	Case-control	June 2012–May 2013	Primary	< 60	Risk factors	Questionnaire	200	Single disease episode	Using solid fuel with location within living area (OR 3.76, 1.20–11.82)
12	Tanzania	PrayGod et al. (2016)	Urban/peri-urban	Case-control	May 2013–March 2014	Primary	< 60	Behaviour	Questionnaire	117	Single disease episode	Cooking indoors increased the risk of developing severe pneumonia (OR 5.5, 1.4–22.1) compared to cooking outdoors
13	Malawi	Mortimer et al. (2017)	Rural	Randomised control trial	December 2013–February 2016	Primary	< 60	Biomass smoke	Questionnaire and exposure measurement	10,543	Mortality and single disease	Cleaner burning biomass-fuelled cookstoves did not reduce the risk of pneumonia in young children under 5 in Malawi
14	Guatemala	Smith et al. (2011)	Rural	Randomised control trial	October 2002–December 2004	Primary	< 18	Household air pollution	Questionnaire and exposure measurement	534	Mortality and single disease episode	Reduction of wood smoke exposure with chimney stoves did not significantly reduce pneumonia in children under 5