A Case–Crossover Study of Wintertime Ambient Air Pollution and Infant Bronchiolitis

Abstract

We examined the association of infant bronchiolitis with acute exposure to ambient air pollutants.DesignWe employed a time-stratified case–crossover method and based the exposure windows on a priori, biologically based hypotheses.ParticipantsWe evaluated effects in 19,901 infants in the South Coast Air Basin of California in 1995–2000 with a hospital discharge record for bronchiolitis in the first year of life (International Classification of Diseases, 9th Revision, CM466.1).Evaluations/MeasurementsStudy subjects’ ZIP code was linked to ambient air pollution monitors to derive exposures. We estimated the risk of bronchiolitis hospitalization associated with increases in wintertime ambient air pollutants using conditional logistic regression.ResultsWe observed no increased risk after acute exposure to particulate matter ≤ 2.5 μm in aerodynamic diameter (PM2.5), carbon monoxide, or nitrogen dioxide. PM2.5 exposure models suggested a 26–41% increased risk in the most premature infants born at gestational ages between 25 and 29 weeks; however, these findings were based on very small numbers.ConclusionsWe found little support for a link between acute increases in ambient air pollution and infant bronchiolitis except modestly increased risk for PM2.5 exposure among infants born very prematurely. In these infants, the periods of viral acquisition and incubation concurred with the time of increased risk.Relevance to Professional PracticeWe present novel data for the infant period and the key respiratory disease of infancy, bronchiolitis. Incompletely explained trends in rising bronchiolitis hospitalization rates and increasing number of infants born prematurely underscore the importance of evaluating the impact of ambient air pollution in this age group in other populations and studies.

Associations of mobile source air pollution during the first year of life with childhood pneumonia, bronchiolitis, and otitis media

“…This is a strength of our study; much of the prior literature has relied either on parental self-report 6, 24, 32, 33, 34, 35 or on emergency department visits and hospitalizations 11,15, 20, 23, 36, 37 which do not capture the less-severe morbidities that are treated in pediatric care offices. Even with these clinical records, however, it is very likely that some children had one or more of the outcomes but were never seen by a doctor particularly due to the similar symptoms that these conditions can have to cold or flu.…”

Tracking Associations Between Ambient Ozone and Asthma-Related Emergency Department Visits Using Case-Crossover Analysis

“…The case-crossover design has been applied in numerous studies to investigate the acute effects of air pollution, including mortality, 13 cardiovascular events, 14-33 and respiratory outcomes. 24,[34][35][36][37][38][39][40] We constructed time-stratified, 41 casecrossover datasets, using 28-day strata. Within a stratum, each case event (an ED visit) was matched to exactly three referent times matched on the same day of the week: that is, at ±7, ±14, and ±21 days.…”

“…The median, average ozone concentrations for cases and referents within categories was 27 (<31 reference), 35 (31)(32)(33)(34)(35)(36)(37)(38)(39), 44 (40-49), 54 (50)(51)(52)(53)(54)(55)(56)(57)(58)(59), and 67 (≥60) ppb. Figure 2 shows a concentrationresponse plot, with 95 percent CIs.…”

Infant exposure to fine particulate matter and traffic and risk of hospitalization for RSV bronchiolitis in a region with lower ambient air pollution

“…Many studies have linked increased exposure to ambient air pollution with increased risk of pediatric respiratory conditions including respiratory infections; however, few epidemiologic data on the infant period and bronchiolitis are available (Karr et al, 2006, 2007). Nonetheless, there is consistent epidemiological evidence of increased infant post-neonatal mortality due to respiratory causes associated with increased exposure to ambient air pollution (Ritz et al, 2006; Woodruff et al, 1997; Bobak and Leon, 1999).…”