Background
The authors write that "respiratory tract infection (RTI) is among the most common acute diseases worldwide, leading to considerable morbidity, complications, and days lost from work and school," citing Mourtzoukou and Falagas (2007). And in this regard they report that the diurnal temperature range (DTR = the difference between the daily maximum and minimum temperatures) "has been identified as an independent risk factor for coronary heart disease (Cao et al., 2009; Tam et al., 2009), stroke (Shinkawa et al., 1990; Kyobutungi et al., 2005; Chen et al., 2007), and chronic obstructive pulmonary disease (Song et al., 2008)."

What was done
Numbers of daily emergency-room visits for RTI at one of the largest medical establishments in Shanghai, China (Huashan Hospital) were collected between 1 January 2008 and 30 June 2009, along with DTR data and data pertaining to possible confounding air pollutants (PM10, SO2 and NO2).

What was learned
After appropriate statistical analyses were conducted by Ge et al., it was determined that increasing DTRs were closely associated with daily emergency-room visits for RTIs, such that "an increase of 1°C in the current-day and in the 2-day moving average DTR corresponded to a 0.94% and 2.08% increase in emergency-room visits for RTI, respectively."

What it means
Since it has long been known that the DTR declines significantly as mean global air temperature rises (Easterling et al., 1997), it can be appreciated that the global warming that occurred prior to its leveling-off some 17 years or so ago likely helped to significantly reduce hospital admissions for RTIs in Shanghai, China, and in much of the rest of the world as well.

References
Cao, J., Chang, Y., Zhao, N., Song, W., Jiang, C., Chen., R. and Kan., H. 2009. Diurnal temperature range is a risk factor for coronary heart disease death. Journal of Epidemiology 19: 328-332.

Chen, G., Zhang, Y., Song, G., Jiang, L., Zhao, N., Chen, B. and Kan, H. 2007. Is diurnal temperature range a risk factor for acute stroke death? International Journal of Cardiology 116: 408-409.

Easterling, D.R., Horton, B., Jones, P.D., Peterson, T.C., Karl, T.R., Parker, D.E., Salinger, M.J., Razuvayev, V., Plummer, N., Jamason, P. and Folland, C.K. 1997. Maximum and minimum temperature trends for the globe. Science 277: 364-367.

Kyobutungi, C., Grau, A., Stieglbauer, G. and Becher, H. 2005. Absolute temperature, temperature changes and stroke risk: a case-crossover study. European Journal of Epidemiology 20: 693-698.

Mourtzoukou, E.G. and Falagas, M.E. 2007. Exposure to cold and respiratory tract infections. International Journal of Tuberculosis and Lung Disease 11: 938-943.

Shinkawa, A., Ueda, K., Hasuo, Y., Kiyohara, Y. and Fujishima, M. 1990. Seasonal variation in stroke incidence in Hisayama, Japan. Stroke 21: 1262-1267.

Song, G., Chen, G., Jiang, L., Zhang, Y., Zhao, N., Chen, B. and Kan, H. 2008. Diurnal temperature range as a novel risk factor for COPD death. Respirology 13: 1066-1069.

Tam, W.W., Wong, T.W., Chair, S.Y. and Wong, A.H.S. 2009. Diurnal temperature range and daily cardiovascular mortalities among the elderly in Hong Kong. Archives of Environmental and Occupational Health 64: 202-206.