In the case of a fever of unknown origin (FUO) or culture-negative sepsis, one might consider the presence of a “doxycycline-deficient state.”
Though you won’t find “doxy deficiency” in your Robbins textbook, the basic concept may be a useful reminder of a list of largely zoonotic infections to consider in the face of diagnostic uncertainty. There is not much in the literature about this concept, so the list below may be incomplete. Let me know if there are others we should add to the list!
“Doxycycline Deficient States”
Q Fever (Coxiella burnetii)
Rocky Mountain Spotted Fever
Jenkins I, Vinetz J. The devil is in the details. J Hosp Med. 2009;4(6):382-386.