Outdoor air pollution and near-fatal/fatal asthma attacks in children: A systematic review

Globally, observational studies have demonstrated an association between high levels of air pollution and asthma attacks in children. It remains unclear whether and to what extent exposure may be associated with increased near-fatal/fatal attacks.

To systematically review the evidence for an association between ambient outdoor air pollution and fatal and/or near-fatal asthma (NFA).

Following Cochrane methodology, we searched MEDLINE, EMBASE, Web of Science, Scopus, and Open Grey electronic databases for studies reporting the association of fatal/NFA and air pollution (particulate matter [PM], sulfur dioxide, nitrogen dioxide, black carbon and ozone [O₃]) in children. NFA was defined as requiring intensive care unit (ICU) management.

Two reviewers independently screened 1358 papers. A total of 276 studies identified asthma attacks related to air pollution, 272 did not meet inclusion criteria after full-text review. Four observational studies described fatal/NFA, of which three addressed NFA. PM2.5 (per 12.5 µg/m³ increase) and O₃ (per 22 ppb increase) were associated with NFA in one study (PM2.5, relative risk: 1.26, confidence interval [CI] [1.10-1.44]), O₃ (1.19 [1.01-1.40]). PM10 was associated with ICU admission in the context of thunderstorm asthma. Elemental carbon was associated equally with NFA that did not require an ICU admission (p = 0.67). Studies of fatal asthma including children did not demarcate age within the analysis.

Ozone and PM2.5 have been associated with NFA in children but synthesis is limited by the paucity of studies and methodological heterogeneity. Poor reporting of severities of asthma attacks hinders the assessment of whether outdoor air pollution is associated with an increased number of NFA/fatal attacks in children.