Predictors of prognosis and risk of acute renal failure in patients with Rocky Mountain spotted fever.

Background: Acute renal failure has long been associated with severe Rocky Mountain spotted fever (RMSF). Despite many descriptions of the protean manifestations of this disease, relatively little is known concerning the risk factors for acute renal failure. Only a few studies have examined the outcome of patients infected with Rickettsia rickettsii who develop renal insufficiency, and these studies had methodological problems.

Objective: To study the incidence, risk factors, and outcomes of acute renal failure in a large group of hospitalized patients with definite or probable RMSF.

Methods: The clinical records of 114 patients with definite or probable RMSF were retrospectively reviewed to identify clinical and biochemical abnormalities at the time of admission that were associated with the development of acute renal failure and subsequent mortality. Renal failure was defined as a serum creatinine (Cr) above 2 mg/dL. Logistic regression was used to study the association between these variables and the outcomes during hospitalization: death and the development of acute renal failure.

Results: The mortality rate in this series was 14%; 19% of the patients developed acute renal failure. The development of acute renal failure increased the odds ratio (OR) of dying by a factor of 17 (P = 0.001). Factors at the time of hospitalization that were associated at a univariate level with subsequent mortality included elevated serum Cr, increased age, increased level of AST, increased level of bilirubin, decreased serum sodium and platelet count, the presence of neurological involvement, and being male. Both the presence of neurological involvement and an elevated serum Cr at presentation were independently associated with increased mortality by multivariate analysis. Three patients developed acute renal failure that required hemodialysis, and only 1 of these 3 patients survived; he was ultimately discharged with a normal serum Cr. Factors at presentation that were associated with the development of acute renal failure included increased bilirubin, increasing age, thrombocytopenia, and the presence of neurological involvement. Both age and decreased platelet count at presentation were independently associated with the development of acute renal failure by multivariate analysis.

Conclusion: Acute renal failure was a frequent complication of RMSF in this series of patients from a tertiary referral medical center. The presence of acute renal failure was strongly associated with death. Clinical and biochemical variables are useful in predicting which patients will develop acute renal failure.