Rapid immunoperoxidase demonstration of Rickettsia rickettsii in fixed cutaneous specimens from patients with Rocky Mountain spotted fever

Immunofluorescence (IF) of skin biopsies for detection of Rickettsia rickettsii (RR) has proven useful as a rapid test for confirmation of Rocky Mountain spotted fever (RMSF). However, IF lacks sensitivity, requires special equipment and training, and is difficult to interpret. The authors have developed an indirect avidin-biotin immunoperoxidase (IP) technique to detect RR in fixed and frozen tissue sections. The technique was evaluated on fixed cutaneous specimens from patients dying of RMSF and compared to specimens from control patients dying of an acute febrile illness with skin manifestations and vasculitis. IP correctly identified RR in 9 of 12 cases with probable identification in 2 additional cases. Of 11 controls, 10 were negative and one was uninterpretable. RR were easily visualized within cytoplasm and nuclei of endothelial cells in association with perivascular lymphocytic infiltrates and less frequently with vasculitis or non-inflamed vasculature. IP is rapid, amplifies small quantities of antigen, gives excellent histologic detail as compared with IF, and is easily adapted for use in hospitals with immunoperoxidase capabilities.