Exposure to Pig Manure May Increase Your Risk for MRSA


If you live near a pig farm or a farm where pig manure is being used for fertilizer, scientists say it may increase your risk for contracting MRSA.

MRSA is an acronym for methicillin-resistant Staphylococcus aureus, a type of bacteria which has become resistant to several different types of antibiotics, including methicillin.  It is of great public health concern because people with weakened immune systems cannot fight it off without help from antibiotics.

Because previous research had found that people working with livestock were at a greater risk for contracting MRSA, the research team decided to study the medical records of people in Pennsylvania who had been treated for infections between 2005-10 in the Geisinger Health System.  Pennsylvania was selected as the site for the study due to state regulations requiring manure from pig farms to be used on agricultural land for fertilizer.

When the researchers analyzed the data for two types of MRSA bacteria called community-associated MRSA (CA-MRSA) and  health-care-associated MRSA (HA-MRSA), they found that the people with the greatest exposure to pig manure had a 38 percent increase in their risk for being infected with CA-MRSA.  They were also 30 percent more likely to contract HA-MRSA.

When the team analyzed skin, blood and sputum collected from 200 of the patients, they did not find any signs of a MRSA strain which had previously been associated with farm animals and agricultural workers called clonal complex 398 (CC398).  However, this strain is not always present in livestock, and it is unknown what strains are most common to the U.S, so this finding does not mean that livestock were not the source of the patients’ infections.

According to one of the authors of the study, Joan Casey, many researchers believe that the ubiquitous use of antibiotics in farm animals is at least partially to blame for the rise in drug-resistant bacteria like MRSA.  And, Casey believes that manure is one medium that is helping these antibiotic-resistant bacteria to spread.

In the past, medical personnel have sought to contain MRSA by using better infection control in hospitals to prevent spreading the bacteria between patients, reducing the number of unnecessary antibiotic prescriptions and encouraging patients to finish their complete course of treatment in order to completely wipe out their infection.  Identifying other ways to combat this problem is very important, however, since antibiotics are a very significant tool that doctors use to fight bacterial infections.  If enough strains of bacteria become resistant to them it could seriously hinder doctors’ ability to take care of their patients and save lives.

More work remains to be done, says Robert Daum, the principal scientist at the MRSA Research Center at the University of Chicago.  He notes that he would like to see the work done by Casey and her team expanded to other geographic areas and studies carried out examining whether the strains found in the infected patients were indeed the same as those carried by the pigs.

The study linking pig manure to increased risk for MRSA was published online on September 16, 2013 in the journal JAMA Internal Medicine.

Written by:  Nancy Schimelpfening

JAMA Internal Medicine

Pig-Manure Fertilizer Linked to Human MRSA Infections

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