Could be blood born, and found a spot inside your body where there was recent disruption. We have bacteria all over the place, inside and out, all the time just looking for a convenient spot to set up shop where the immune system may be challenged. Anywhere the tissue has been disrupted is more susceptible to those bacteria settling in.
Wash your hands EVERY time you are outside for any reason, or even inside at those important times, but especially after being with the chickens. It will take weeks before your tissues recovery, no matter if you are cleared to go back to work or not.