Background
The authors write that "childhood asthma is a major global health issue, affecting more than 300 million people worldwide (Baena-Cagnani and Badellino, 2011)," while further noting that it "is regarded as a national health priority in several countries," citing Asher et al. (1995, 2006). And in light of the disease's growing notoriety, they decided to study the relationship between diurnal temperature range (DTR) and the incidence of childhood asthma in Brisbane, Australia.

What was done
In the words of Xu et al., "a Poisson generalized linear model combined with a distributed lag non-linear model was used to examine the relationship between DTR and emergency department admissions for childhood asthma in Brisbane from January 1st 2003 to December 31st 2009," while daily maximum and minimum temperatures in Brisbane for the same time period were retrieved from the Australian Bureau of Meteorology, after which each day's DTR was calculated as the difference between its maximum and minimum temperatures.

What was learned
The six scientists report discovering that "childhood asthma increased above a DTR of 10°C," and "was the greatest for lag 0-9 days, with a 31% increase in [hospital] emergency department admissions per 5°C increment of DTR," while further noting that "male children and children aged 5-9 years appeared to be more vulnerable to the DTR effect than others."

What it means
Since daily minimum temperatures have nearly always risen faster than have daily maximum temperatures in most locations around the globe whenever various regions have warmed, it can be appreciated that during a period of global warming, the DTR typically decreases, which thus leads to a decline in the number of cases of childhood asthma, as has also been shown to be the case for a number of other human maladies. See, for example, the many items archived under the general heading of Health Effects (Temperature) in our Subject Index.

References
Asher, M., Keil, U., Anderson, H., Beasley, R., Crane, J., Martinez, F., Mitchell, E., Pearce, N., Sibbald, B. and Stewart, A. 1995. International study of asthma and allergies in childhood (ISAAC): rationale and methods. European Respiration Journal 8: 483-491.

Asher, M.I., Montefort, S., Bjorksten, B., Lai, C.K.W., Strachan, D.P., Weiland, S.K. and Williams, H. 2006. Worldwide time trends in the prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and eczema in childhood: ISAAC Phases One and Three repeat multi-country cross-sectional surveys. Lancet 368: 733-743.

Baena-Cagnani, C. and Badellino, H. 2011. Diagnosis of allergy and asthma in childhood. Current Allergy and Asthma Reports 11: 71-77.