A University of Iowa study says children living near a pork production site, especially where subtherapeutic antimicrobials are fed, are more likely to have asthma than other children.

Researchers examined 644 children from birth to age 17, living in Keokuk County, Iowa. They considered other asthma risk factors, including premature birth, respiratory infections at a young age, personal history of allergies and family history of allergies.

The study indicates that 55.8 percent of children living on pork operations using subtherapeutic antibiotics had at least one health indicator of asthma. That compares to 26.2 percent of children on farms that don’t have hogs.

"We believe that some of the increase in asthma risk is related to occupational and bystander exposures in animal feeding operations," according to the study's author, James A. Merchant, dean of the College of Public Health and an environmental health professor.

Farms that use subtherapeutic antibiotics tend to be larger, but Merchant says the research team concluded antibiotic exposure might play some role in the development of childhood asthma.

Although Merchant says researchers are certain that the kids who were working in or as bystanders or close to those facilities are getting exposed to antibiotic-laden dust, he contends further study needs to be done to determine what role the antibiotics in feed plays.

In addition, study findings indicate that 42.9 percent of children on farms with less than 500 pigs had signs of asthma while 46 percent on farms with more than 500 pigs had asthma indicators. Researchers also found that 33.6 percent of children not living on a farm and not around hogs had at least one indicator of asthma.

Questioning the study is Iowa state representative and pork producer, Sandra Greiner, who along with her husband and three sons raised hogs in eastern Iowa for decades and developed no health problems.

National Pork Board officials point out that the study contradicts numerous studies showing that “farm kids” have fewer allergies and lower asthma rates than non-farm children. Also there are questions about the terminology used within the study.

Paul Sundberg, DVM, vice president of science and technology for NPB, cautions that this is an epidemiological survey study. This type of research looks for statistical associations and trends, but don’t prove them.

For instance, Sundberg notes that the fourth point NPB provided in response to the study, all of the listed factors can be associated with asthma, but don’t all cause asthma.

Here’s a list of NPB’s points in response to the study:

  1. This study is at odds with numerous studies indicating that farm children often have fewer allergies and lower rates of asthma than non-farm children.
  2. As recognized by the authors, asthma risk is conveyed by a complex interaction of genetic and environmental determinants.
  3. In this study, farm exposure to swine was associated to fewer asthma determinants than: male gender, age, personal history of allergies, and early respiratory infection. 
  4. In the multivariable analysis gender, age, history of allergies, family history of allergies, premature birth, early respiratory infection, high risk birth, and living on a farm that raises swine/added antibiotics to feed were all significantly associated with the four asthma outcomes.
  5. Children currently living on a farm were somewhat less likely to have allergies.
  6. The mean number of hogs on farms that used antibiotics was 750 versus 392 for farms that did not use antibiotics. Neither of these approached the size definition of a CAFO (Confined Animal Feeding Operation) – indeed the 750 is approximately 25 percent of the number of animals.   It is somewhat deceptive of the report to use the term AFO (Animal Feeding Operation) as for persons unfamiliar with the industry it is likely to be confused with the term CAFO. 
  7. This study suggests that antibiotic use might be a marker for farm size. The USDA’s National Animal Health Monitoring System (NAHMS) surveys a statistically valid sample of farms to represent the national swine herd.  In their last swine report there was no difference in the percent of farms reporting using antibiotics in feed between the small farms (10,000 inventory).

Merchant acknowledges that asthma is a complex condition that may be caused by several genetic and environmental factors, but says the study should heighten the awareness of swine farm parents that their children may face an increased risk of asthma.

He also says the study was limited to close exposure by children living on pork operations and doesn’t suggest a higher risk for neighbors living downwind from the farm.

National Pork Board and Environmental Health Perspectives