Table 4.

Studies that examine the effect of meteorological factors on HAs.

Meteorological risk factors
Location	Author	Sample size	Temperature	Relative humidity	Thunderstorm	Wind speed	Rainfall	Key measures	Results
Europe
Cardiff and Newport, UK	Anderson et al. [14]	2000			YES		YES	Min./max. temperature and total daily rainfall	Average daily asthma hospitalization was lower during the summer (4.1, May–September, p=0.04). More admissions occurred during thunderstorms (p=0.04); however, there was no relationship between rainfall and admissions
North America
Los Angeles, USA	Delamater et al. [16]	250, 000	YES	YES				Max. temperature and relative humidity	HAs increased during winter (0.481 per 100,000 admissions)
New York, USA	Fitzgerald et al. [11]	237, 639	YES			YES		Cold spells lasting three days, where the daily mean temperature was less than the 10th percentile for a given month and region	HAs increased in November (mean = 9.6, 95% CI: 5.5% to 13.9%) and April (mean = 5.0, 95% CI: 1.2% to 9.0%)
Maryland, USA	Soneja et al., 2016	115, 923	YES				YES	Daily max. temperature and total daily precipitation	Extreme heat increased HAs by 3% (OR: 1.03, 95% CI: 1.00 to 1.07)
South Asia
Bangalore, India	Kunikullaya et al., 2017	1768	YES	YES			YES	Max./min./average temp., relative humidity, and total daily rainfall	Average daily asthma admission was 4.84 ± 2.91, had seasonal variation and increased during the cold season (p=0.015)
Middle East
Kuwait	Qasem et al. [20]	4353	YES	YES		YES	YES	Daily temperature, relative humidity, and total daily rainfall	Hospitalization increased during December due to high temperatures (mean = 39.7, p < 0.03)
East Asia
Shanghai, China	Zhang et al. [9]	15, 678	YES	YES		YES	YES	Min./max. and mean temperature, relative humidity, and total daily rainfall	RR: 1.20 (95% CI: 1.01 to 1.41) for lower temperatures
Hong Kong	Lam et al. [19]	56, 112	YES	YES		YES		Daily mean temperature and mean relative humidity	Cumulative risk of hospitalizations during the hot season was 1.19 (95% CI: 1.06 to 1.34)