Clinical features of RMSF:
(1) patient with a febrile illness residing or traveling to an endemic area
(2) history of potential tick exposure, typically a dog or wood tick, from the spring to fall
(3) in addition to fever, patients may present with headache, myalgias and gastrointestinal disturbances (diarrhea, jaundice)
(4) a rash appears a few days after disease onset, usually starting on the ankles or wrists, later becoming petchecial or purpuric in nature.
(5) if generalized spread occurs, there is a vasculitis with endothelial cell injury, leading to edema, hypovolemia, hypotension, and a disseminated intravascular coagulopathy. Patients with severe disease may have encephalitis, adult respiratory distress syndrome, renal failure, cardiac arrhythmias or tissue necrosis.
Risk factors for fatal outcome in RMSF (after Table 2, Thorner et al, 1998):
(1) male gender
(2) non-Caucasian
(3) age > 40 years
(4) no history of tick attachment
(5) absence of headache
(6) gastrointestinal tract symptoms
(7) delay in diagnosis (absence of rash, atypical symptoms, off season presentation)
(8) no treatment by the fifth day of illness
(9) glucose-6-phosphatase dehydrogenase (G6PD) deficiency (associated with a fulminant hemolytic syndrome)
In the review by Childs and Paddock:
(1) Some of the risk factors (no history of tick attachment, delay in diagnosis, delay in treatment) relate to failure to start adequate therapy early in the course of the disease.
(2) The increased risk for male gender is inconsistent and may have been related to increased occupational exposure rather than increased susceptibility.
(3) The increased risk for non-Caucasians is inconsistent and may be related to other factors such as reduced medical access, difficulty in detecting a rash, and a higher incidence of G6PD deficiency.
(4) The increased risk associated with age continues to increase as the person ages beyond 40 years.
(5) Failure to give effective antibiotics is also a risk factor.
