Abstract
This population-based study examines the incidence of gastroschisis in California over time and by county.
The incidence of gastroschisis is increasing worldwide, but the causes and risk factors of this increase are not well elucidated.1 This study examines the incidence of gastroschisis in California over time and by county.
Methods
This was a population analysis using data from the Linked Birth Database from the California Office of Statewide Health Planning and Development from 1995 to 2012, which includes information on all births in California. Patients with gastroschisis were identified by an International Classification of Diseases-Ninth Edition (ICD-9) procedure code for gastroschisis repair (54.71), ICD-9 diagnosis code for gastroschisis (756.73, available since 2009), or birth certificate designation for gastroschisis (available since 2006). We performed the study from July to December 2017. This study was approved by the UC Davis Institutional Review Board and the California Committee for the Protection of Human Subjects, which waived informed patient consent for deidentified data.
Counties were identified as rural, partially rural, and metropolitan, according to 2010 census data.2 Agricultural counties were identified based on gross value of agricultural production (nontimber and timber) by county in 2012.3
Annual incidence rates of gastroschisis by county of residence were calculated. Logistic regression analyses were used to assess the association between county, year, rural setting, and agricultural production and the risk of gastroschisis. Primary analysis was logistic regression. Statistical analysis was performed using Stata/SE, version 14.2 (StataCorp).
Results
The rate of gastroschisis increased from 1.7 cases per 10 000 births in 1995 to 5.3 cases per 10 000 births in 2012 (overall, 2.7 cases/10 000 births) (Figure 1). Overall incidence was highest in Modoc, followed by Mariposa, Siskiyou, Lake, Shasta, Mendocino, Nevada, Amador, Humboldt, Glenn, and El Dorado counties (5.1-20.9 cases/10 000 births) (Figure 2). Incidence was lowest in Inyo, Ventura, San Luis Obispo, Los Angeles, Santa Cruz, Tulare, San Mateo, San Diego, Fresno, Santa Clara, Sonoma, San Benito, Kings, Del Norte, Contra Costa, Orange, San Francisco, Solano, Yuba, Madera, Alameda, and Marin counties (0.9-2.7 cases/10 000 births). No cases were reported in Alpine, Lassen, Sierra, or Trinity counties.
Figure 1. Incidence of Gastroschisis per 10 000 Births Over Time in California.
The incidence increased between 1995 and 2012.
Figure 2. Incidence of Gastroschisis in California by County.
Overall incidence (A) and change in incidence over time (B) from 1995 to 2012.
Incidence decreased in Plumas, Solano, Yuba, Nevada, Glenn, Humboldt, and San Benito counties (Figure 2). Incidence increased by more than 1 case per 10 000 births per year in Mono, Mariposa, Colusa, Siskiyou, and Modoc counties.
Univariate logistic regression demonstrated an increased odds ratio (OR) of gastroschisis in rural (OR, 3.04; 95% CI, 2.37-3.89; P < .001) and partially rural counties (OR, 1.60; 95% CI, 1.42-1.81; P < .001) compared with metropolitan counties. These findings were consistent when adjusting for race/ethnicity, year, insurance status, maternal age, and fetal drug exposure on multivariable analysis (compared with metropolitan counties, rural counties: OR, 1.75; 95% CI, 1.35-2.28; P < .001; partially rural counties: OR, 1.24; 95% CI, 1.09-1.40, P = .001).
On univariate analysis, when ranking counties by gross agricultural value, middle- (OR, 1.31; 95% CI, 1.17-1.48; P < .001) and high-ranking counties (OR, 1.37; 95% CI, 1.22-1.55; P < .001) had higher odds of gastroschisis compared with low-ranking counties. The risk of gastroschisis was also higher among the top 5 counties with the highest timber gross values compared with all other counties (OR, 2.45; 95% CI, 1.89-3.17; P < .001).
Discussion
The incidence of gastroschisis is increasing in California and the risk is higher in rural counties. When categorizing county by agricultural value, risk was greater in counties with higher gross agricultural value, but risk was greatest in areas of high timber value.
Although previous studies have hypothesized increased risk in agricultural areas because of atrazine exposure,4,5 one of the most common herbicides used in the United States, this herbicide is rarely used in forested areas and is more commonly used for corn in the Midwest. A previous study in the San Joaquin Valley in California from 1997 to 2006 also did not find evidence of this association.6 The primary limitation of this study is that it was retrospective and observational, using an administrative database, and thus relied on accurate coding.
The rising risk of gastroschisis in rural counties in California is not clearly owing to agricultural exposures. Future studies should consider other risk factors that may be more common in these areas.
References
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