BACKGROUND: In August 2012, a health care provider notified the Washington State Department of Health (DOH) of several cases of anencephaly, a neural tube birth defect (NTD), in rural Benton, Franklin, and Yakima counties. DOH verified an increased rate of 8.1 per 10,000 live births from January 2010-January 2013, nearly four times the estimated national rate of 2.1 per 10,000 live births in 2010 and began an investigation to explore possible causes for the increase.
METHODS: DOH conducted surveillance of NTD cases in the area identifying potential cases from hospital medical records, physician report, and vital statistics data. All potential cases were confirmed by ultrasound, pathology report, or physician examination. To examine possible causes, we compiled descriptive epidemiology, conducted a medical records based case-control study, explored the potential for high nitrates in drinking water and residential proximity to agricultural lands, and interviewed case mothers using a modified version of the National Birth Defects Prevention Study questionnaire.
RESULTS: From January 2010 - November 2016, DOH confirmed 73 NTD cases in the three-county area, including 45 anencephalic infants (62%). From 2010-2015 the three-county area experienced an anencephaly rate of 8.2 per 10,000 live births, and an overall NTD rate of 12.7 per 10,000. Cases did not appear to be concentrated in time, seasonally across years, or geographically within the three county area. Both Hispanic and Non-Hispanic whites had elevated rates of anencephaly. Almost 80% of case and control mothers received public residential water supplies. Public residential nitrate concentrations were lower than the EPA-defined Maximum Contaminant Level (MCL) of 10mg/L. Case and control mothers lived similar distances from agricultural lands. Fifty-five percent of mothers of anencephalic infants who were approached agreed to be interviewed. Interviews did not reveal any unique exposures, but the low proportion of Washington mothers interviewed may not have represented all case mothers. Fifty-one percent of anencephaly cases ended at less than 20 weeks gestation, higher than reports of NBDPS anencephaly cases from California and Texas.
CONCLUSIONS: Neither the descriptive epidemiology, the medical records case-control study, investigation of drinking water nitrates, proximity to agricultural land or interviews of case mothers identified a preventable cause. It is likely that case ascertainment was more complete than elsewhere, resulting in some exaggeration of the magnitude of the increase. DOH is continuing to partner with local health and others to promote preconception folic acid use and access to care as prevention strategies.