Methicillin-resistant Staphylococcus aureus (MRSA) is often found, both airborne and in settled dust, on pig farms, and is considered an occupational health problem. At NFA, we have studied the average particle sizes of airborne S. aureus and MRSA and their rate of decay in air and dust samples, respectively, from six pig farms.
On average, the particle size fractions potentially depositing in the upper airways constituted 70%, in the primary and secondary bronchi 22%, and in the terminal bronchi and alveoli 8% of the inhalable MRSA and S. aureus concentration. The concentration of airborne MRSA and S. aureus, as well as the fraction potentially depositing in the different parts of the airways, depended on the specific work task being performed and the specific location on the farm.
The rate of decay of S. aureus and MRSA was measured in 196 dust samples. Storage time significantly reduced the bacterial loads, and the half-life for both S. aureus and MRSA was five days. The 99.9% die-off rate was 66 days for MRSA.
Thus, S. aureus and MRSA on pig farms pose a double risk:
- People inside the farm are at risk of inhaling the bacteria all the way into the lowest parts of the airways, and
- dust containing living bacteria transported, e.g. on clothing, outside the farm can be found as living bacteria for more than 30 days after leaving the stable, and thus in the period pose a risk for susceptible individuals.