A novel hypothesis to explain traffic-related nocturnal cough.

摘要

I am writing to comment on the paper entitled "Respiratory health and individual estimated exposure to traffic-related air pollutants in a cohort of young children" (Occup Environ Med 2007;64:8-16). The paper looked at the health effects of various components of air pollution as they depended on distance from major traffic arteries in and around Munich, Germany.The key finding I want to examine is the observed association of ambient nitrogen dioxide (NO2) levels and nocturnal cough in very young children.Morgenstern's Table 4 shows that NO2 concentrations varied from 19.4 to 71.7 礸/m3, with a mean of 35.4. Those concentrations are much lower than those that have been demonstrated to have harmful effects, at least in adults. According to one authoritative review1 there is little evidence that NO2 has any respiratory effect, even on asthmatics, at concentrations less than 200 ppb (376 礸/m3).A review2 of the health effects of outdoor NO2 concluded:. "The overall results suggest that outdoor NO2 was serving as a marker for more causal agents ..." That conclusion obviously suggests that there may be a missing (unknown) pollutant that can, in some circumstances, mimic NO2 in ecological studies.The idea that NO2 may have harmful effects on young children is not new. However, the existing literature could be described as conflicting, with one study of indoor NO2 at concentrations in the range 60-300 pg/m3 finding no effect in children aged 6-9 years. I found several papers that found no such association, including some that looked at infants. These results make it unlikely that NO2 itself was the direct cause of the cough.