A Case Cluster Conundrum of Flea-Borne Rickettsiosis: Is Rickettsia felis or Rickettsia typhi to Blame?

Dear Dr. Rothwell, We read with interest the article titled “Rickettsia felis Case Cluster in a Military Family” by Stidham and colleagues published in the November-December issue. The article highlights important considerations for health care professionals and public health authorities in areas endemic for flea-borne typhus, the disease caused by Rickettsia typhi (also known as murine or endemic typhus). In this report, a boy with a history of a hemoglobinopathy presented to an emergency department with a febrile illness, rash, and foot/ankle pain. The boy was empirically treated for a rickettsial infection, and indirect immunofluorescence assay (IFA) for spotted fever group (SFG) and typhus group (TG) rickettsiae were both reactive at IgG titers of 1:256. Interestingly, follow-up testing 12 days after the first failed to show a change in antibody titers. The boy and his family had recently moved into on-post housing with a preexisting flea infestation. Family members also experienced a febrile illness, were empirically treated with doxycycline, and had reactive antibody titers with variable results in isoform reactivity (IgM versus IgG) and antigenic group activity (TG versus SFG). The family’s home underwent insecticide treatment, and fleas were collected for eventual molecular testing. Seven of 17 tested fleas had evidence of harboring Rickettsia felis. Based on these results, the authors conclude R. felis was the likely infectious culprit.