Morris J K, Alberman E, Mutton D
Department of Environmental and Preventive Medicine, Wolfson Institute of Preventive Medicine, St Bartholomew's and the Royal London School of Medicine and Dentistry, UK.
Int J Epidemiol. 1998 Jun;27(3):495-8. doi: 10.1093/ije/27.3.495.
Associations between environmental hazards and the occurrence of congenital anomalies may be detectable by seeking evidence of non-random occurrence of cases (clusters). There have been a number of anecdotal reports of occurrences of clusters of Down syndrome (DS).
Data from a national register of cytogenetic diagnoses of Down syndrome births and legal terminations occurring between 1989 and 1995 were used to examine the possibility of clustering. Space-time clustering at Regional Health Authority (RHA) level was examined by comparing the expected monthly number of DS pregnancies given the maternal age distribution, with the observed numbers. Knox's method was used to determine if any clustering of RHA of unexpectedly high prevalence had occurred. Seasonality was also investigated by comparing monthly expected and observed numbers of DS pregnancies. Time clustering was examined by using the scan statistic to determine whether a statistically significant excess of pregnancies in any 3-month period occurred in any individual or adjacent groups of District Health Authority (DHA).
The numbers of DS pregnancies were no higher than expected (P < 0.05) in the same RHA over consecutive months. There was no evidence of any seasonality of DS pregnancies (P > 0.5). Only two individual DHA and three pairs of adjacent DHA had significantly high scan statistics (P < 0.03), but as over 400 statistical tests had been completed 12 clusters would be expected to have occurred due to chance alone.
There was no evidence of any space-time clustering in DS at DHA level.
通过寻找病例非随机发生（聚集）的证据，可能会发现环境危害与先天性异常发生之间的关联。已有多篇关于唐氏综合征（DS）聚集病例发生的传闻报道。
利用1989年至1995年间全国唐氏综合征出生及合法终止妊娠的细胞遗传学诊断登记数据，研究聚集的可能性。通过比较给定孕产妇年龄分布情况下DS妊娠的预期月数与观察到的月数，来检验地区卫生管理局（RHA）层面的时空聚集情况。采用诺克斯方法确定是否存在患病率意外高的RHA聚集情况。还通过比较DS妊娠的预期月数和观察到的月数来研究季节性。利用扫描统计量检验时间聚集情况，以确定在任何单个或相邻的地区卫生管理局（DHA）中，在任何3个月期间是否出现统计学上显著过量的妊娠情况。
在同一RHA中，连续几个月的DS妊娠数不高于预期（P < 0.05）。没有证据表明DS妊娠存在任何季节性（P > 0.5）。只有两个单独的DHA和三对相邻的DHA扫描统计量显著偏高（P < 0.03），但由于已完成400多次统计检验，仅因偶然因素预计就会出现12个聚集情况。
没有证据表明在DHA层面DS存在任何时空聚集情况。
