While photochemical oxidants (Ox = O3+ NO2) are known to increase asthma flare-ups, there is a paucity of studies of the Japanese population, especially for Tokyo residents. We used data on asthma cases (n = 7,455) from ambulance dispatches in Tokyo, 2015-2016. Variables included date and time of incidence, age, sex, occurrence location at the ward (ku) level, and the symptom/cause of dispatch as recorded by paramedics. Ox data were obtained from the nearest air quality monitoring station to the occurrence location, then linked them with the outcomes based on occurrence date. We directly incorporated a distributed lag model into a bi-directional case-crossover study design controlling for ambient temperature and day of week. A 10-ppb increase in Ox for lag days 0-3 was associated with a 5.51% (95% CI: 0.13 to 11.18) increase in ambulance dispatches related to asthma. The association was strongest on lag day 1 (4.67%, 95% CI: 0.51 to 9.00). Exposure to high levels of Ox was associated with increased ambulance dispatches related to asthma exacerbations in Tokyo, Japan.
Keywords: Asthma; Ox; Tokyo; asthma exacerbations; asthma flare-ups; case-crossover study; distributed lag model; japan; o3; ozone; photochemical oxidants.