Author:
Abbah Achenyo Peace,Xu Shanshan,Johannessen Ane
Abstract
BackgroundFew studies have investigated the association between long-term exposure to outdoor air pollution and the risk of asthma and respiratory symptoms in low-and middle-income countries (LMICs).ObjectiveTo systematically evaluate the epidemiological evidence regarding the associations between long-term exposure to outdoor air pollution and respiratory symptoms in LMICs.MethodsWe searched for literature published between January 1946 and September 2022 in Embase (Ovid), Medline (Ovid), and Web of Science (Core Collection). The air and gaseous pollutants studied included particulate matter (PM2.5 and PM10), nitrogen dioxide (NO2), and black carbon (BC), and exposure was 1-year duration or more. We conducted a systematic review and meta-analysis with a random-effects model to calculate the relative risk (RR) estimates. A rerun of the databases was conducted in November 2023 with no eligible studies found.ResultsOf the 1,346 studies identified, only six met our inclusion criteria, and these six reported PM2.5, PM10, and NO2 with asthma as the main outcome. Three of these included studies were further included in the meta-analysis because they had data on the same exposure and outcome (PM2.5 and asthma). The main result of our study showed a borderline significant association between a 10 µg/m3 increase in exposure to PM2.5 and an increased risk of asthma (RR 1.21, 95% CI 0.93, 1.50). There was evidence of considerable heterogeneity (I2 = 75.87%). The regression-based Egger test for small-study effects showed no significant publication bias among these three studies.ConclusionOur results indicate that long-term exposure to PM2.5 increases the risk of asthma in LMICs, but studies are scarce and there is a large need for more research in LMICs in this field.Systematic Review Registrationhttps://journals.plos.org/plosone/article?id=10.1371/journal.pone.0288667, PROSPERO (CRD42022311326).