In February 2026, a highly pathogenic avian influenza (HPAI) A(H5N1) outbreak in a poultry holding in Sigmaringen, Germany, affected poultry and domestic cats, with infection confirmed by RT-qPCR. A One Health investigation identified 17 exposed humans, one of whom developed respiratory symptoms but tested negative for HPAI A(H5N1) (human coronavirus OC43 detected). Serological testing used haemagglutination inhibition assays. This outbreak highlights zoonotic risk, mammalian spillover and the need for coordinated veterinary and public health response and preventive measures.