Dermatitis outbreak associated with <i>Pyemotes herfsi</i> mites among animal shelter workers and volunteers in Wisconsin, a case study from September 2023

During September 2023, five animal shelter workers reported developing dermatitis after contact with dry pet food bags donated by a pet store. We investigated to determine outbreak source and mitigate further spread. A case was defined as the onset of pruritus within 12 hours of contact with pet food bags or surfaces contaminated by them, occurring between September 1 and 8, 2023, in any setting. We interviewed persons presenting pruritis and requested photographs of their lesions, which a dermatologist reviewed. In total, seven cases were identified, including five among shelter workers and two among drivers who handled the pet food donation. Six (86%) persons reported contact with the exterior of donated pet food bags; all six persons who touched the unopened pet food bags experienced dermatitis. The dermatologist determined lesions were consistent with arthropod exposure. To assess arthropod contamination on the pet food bags, we adhered masking tape to their exterior and collected ≥20 samples; an entomologist examined these samples. Itch mites, <i>Pyemotes herfsi,</i> were present on all pet food bag samples. Although <i>Pyemotes</i>-associated outbreaks are rare in public health literature, practitioners can consider raising awareness of this dermatitis source.