Background
The authors write that "no previous study exists in China examining the impact of extreme temperature on morbidity outcomes," so they decided to investigate the impact of heat waves and cold spells on hospital admissions in Shanghai, China.

What was done
Working with weather data they obtained from the Shanghai Meteorological Bureau, Ma et al. first defined heat wave as a period of at least seven consecutive days with daily maximum temperature above 35.0°C and daily average temperatures above the 97th percentile during the study period, while they defined cold spell as a period of at least seven consecutive days with daily maximum temperature and daily average temperatures below the 3rd percentile during the study period. Then, for one heat wave (24 July to 2 August, 2007) and one cold spell (28 January to 3 February, 2008), they obtained daily hospital admission data for these periods from the Shanghai Health Insurance Bureau.

What was learned
The four researchers report that the number of excess (above normal) hospital admissions during the eight-day heat wave was 352 - driven by a 2% increase in all-cause admissions, an 8% increase in admissions due to cardiovascular problems, and a 6% increase in admissions related to respiratory problems - while during the ten-day cold spell there were 3725 excess admissions, driven by 38%, 33% and 32% increases in admissions due to all-cause, cardiovascular and respiratory problems, respectively.

What it means
In a rather low-key discussion of their findings, Ma et al. say "the cold spell seemed to have a larger impact on hospital admission than the heat wave in Shanghai," which also appears to be the case in most other locations around the world where similar analyses have been performed, as may be seen by perusing the items we have archived under the heading of Health Effects (Temperature - Hot vs. Cold Weather) in our Subject Index.