Haibin Han,1 Jie Liu,1 Lu Wang,1 Gen Li,2 Tingting Wang1 

1Department of Psychiatry, Qingdao Mental Health Center, Qingdao, Shandong, People’s Republic of China; 2Department of Spinal Surgery, Qingdao Huangdao Central Hospital, Qingdao, Shandong, People’s Republic of China

Correspondence: Tingting Wang, Department of Psychiatry, Qingdao Mental Health Center, Qingdao, Shandong, People’s Republic of China, Email wtt06309302@163.com

Purpose: This study aimed to quantify the effects of humidex (a composite index of temperature and relative humidity) on schizophrenia admissions.
Methods: The exposure-lag-response relationship between humidex and schizophrenia admissions was explored via a distributed lag nonlinear model (DLNM). The modification effects of sex and age were also investigated. We further calculated the attributable fraction (AF) and number (AN) due to humidex.
Results: During the study period, the median humidex in Qingdao was 15.22, and the low humidex (− 7, 2.5th percentile) and high humidex (40, 97.5th percentile) were − 7 and 40, respectively. The significant adverse effects of low humidex on schizophrenia admissions persisted from lag 2 [Relative risk (RR)=1.060, 95% CI (confidence interval): 1.006– 1.117] to lag 5 (1.063, 1.008– 1.122) and reached its maximum at lag 4 (1.078, 1.008– 1.152). Females and young individuals are susceptible to low humidex. In addition, the AFs and ANs of schizophrenia admissions due to low humidex were 7.2% and 407, respectively.
Conclusion: Schizophrenia admission was associated with only low humidex. Humidex may serve as an early warning indicator of schizophrenia.

Keywords: distributed lag nonlinear mode, relative risk, humidex, attributable fraction