Links Between Manured Fields and Human Health.

Background: Industrial food animal production produces hundreds of millions of tons of manure each year, most of which is spread untreated on agricultural fields. People living nearby may be exposed to chemical and microbial contaminants, which may have health impacts including methicillin-resistant Staphylococcus aureus (MRSA) infections and negative birth outcomes.

Methods: We used electronic health record data from a health care system in Pennsylvania spanning 2005-2013 to conduct two studies. In the first, we identified 1359 community-associated MRSA cases and 2895 skin and soft tissue infection (SSTI) cases and frequency matched them to 2914 controls. In the second, we performed a retrospective cohort study of 9384 mothers and 10946 neonates using term birth weight, preterm birth, low 5 minute Apgar score, and small for gestational age as outcomes. We created exposure to swine and dairy manured crop fields based on the inverse-distance squared between patient addresses and fields, the amount of manure applied, and the size of the field.

Results: In adjusted analysis, dairy crop field exposure was associated with community-associated MRSA infections and swine crop fields were associated with both community-associated MRSA infections and SSTIs (1.38 [95% CI, 1.13-1.69] and 1.37 [95% CI, 1.18-1.60], respectively). In another analysis, exposure to manure-applied crop fields was associated with preterm birth (2.02 [95% CI, 1.47-2.77]). Crop field exposure was not associated with the other three birth outcomes assessed. Both analyses accounted for patients nested in communities and, in the second study, births nested in mothers.

Conclusion: Residence near manured fields was associated with three health outcomes. Researchers should link direct environmental sampling with health outcomes to help explain biologic mechanisms and highlight areas for intervention.