A case-control study of sudden unexplained nocturnal death syndrome in the southern Chinese Han population

To study the epidemiological characteristics of sudden unexplained nocturnal death syndrome (SUNDS) in the southern Chinese Han population during 2007 to 2013, we gathered 879 SUNDS victims from Dongguan City and in the Longgang District in Shenzhen City as the case group then selected 879 all-cause death cases, adopting a 1:1 pair method, as the control group I and collected 8142 all-cause death cases from the Bao'an District in Shenzhen City as the control group II, simultaneously. Case information collected was statistically analyzed. The annual incidence of SUNDS is 1.02 and 2.23 per 100,000 person-years for Dongguan City and in the Longgang District, respectively. The number of male and female victims is drastically different, with a ratio of 13.92:1, whereas the incidence between the 2 sexes is significantly different (χ2 = 78.734, P < 0.01), with an odds ratio value of 11.32 (95% confidence interval, 5.75-22.28). The age of death of SUNDS cases ranges from 17 to 55 years with a median age of 35 years; furthermore, the difference of distribution of age of death between the SUNDS victims and the all-cause death population is significant (χ2 = 767.12, P < 0.001). The birthplace of SUNDS victims is distributed throughout 27 provinces of China, but the difference between the SUNDS victims and the all-cause death population is not significant (χ2 = 27.273, P > 0.05). The monthly incidence of SUNDS is relatively higher from March to June, whereas the difference of monthly distribution between SUNDS victims and all-cause death population is significant (χ2 = 9.869, P < 0.05), with an odds ratio value of 1.42 (95% confidence interval, 1.14-1.76). Although the majority of SUNDS occurred during midnight sleep, they were mostly discovered from 7 to 9 am once the inmates or spouses woke in the morning. A total of 97.74% of the SUNDS victims were blue-collar factory workers with a high-intensity labor and poor education background. This investigation confirmed the stability of epidemiological characteristics of SUNDS in South China and implicated that risk factors of this fatal disease still exist. The efficient strategy of early identification such as molecular diagnosis for SUNDS is extremely urgently required.