Risk Factors for Fatal Outcome From Rocky Mountain Spotted Fever in a Highly Endemic Area—Arizona, 2002–2011

Abstract

Background Rocky Mountain spotted fever (RMSF) is a disease that now causes significant morbidity and mortality on several American Indian reservations in Arizona. Although the disease is treatable, reported RMSF case fatality rates from this region are high (7%) compared to the rest of the nation (<1%), suggesting a need to identify clinical points for intervention. Methods The first 205 cases from this region were reviewed and fatal RMSF cases were compared to nonfatal cases to determine clinical risk factors for fatal outcome. Results Doxycycline was initiated significantly later in fatal cases (median, day 7) than nonfatal cases (median, day 3), although both groups of case patients presented for care early (median, day 2). Multiple factors increased the risk of doxycycline delay and fatal outcome, such as early symptoms of nausea and diarrhea, history of alcoholism or chronic lung disease, and abnormal laboratory results such as elevated liver aminotransferases. Rash, history of tick bite, thrombocytopenia, and hyponatremia were often absent at initial presentation. Conclusions Earlier treatment with doxycycline can decrease morbidity and mortality from RMSF in this region. Recognition of risk factors associated with doxycycline delay and fatal outcome, such as early gastrointestinal symptoms and a history of alcoholism or chronic lung disease, may be useful in guiding early treatment decisions. Healthcare providers should have a low threshold for initiating doxycycline whenever treating febrile or potentially septic patients from tribal lands in Arizona, even if an alternative diagnosis seems more likely and classic findings of RMSF are absent.

Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis — United States

“…On the three most affected reservations, the average annual incidence rate for 2009-2012 was approximately 1,360 cases per million persons (17). The 7%-10% case-fatality rate in these communities, which is the highest of any region in the United States, has been associated predominantly with delayed recognition and treatment (4,18).…”

“…Therefore, absence of a recognized tick bite should never dissuade health care providers from considering tickborne rickettsial disease in the appropriate clinical context. In fact, the absence of classic features, such as a reported tick bite, has been associated with delays in RMSF diagnosis and increased risk for death (9,18,74,75). The location of the tick bite might be obscure, and the bite is typically painless.…”

“…Children aged <15 years more frequently have a rash than older patients and develop the rash earlier in the course of illness (6)(7)(8). Lack of rash or late-onset rash in RMSF has been associated with delays in diagnosis and increased mortality (6,18,74). Unlike some SFG rickettsioses, an inoculation eschar is rarely present with RMSF (100,101 features that have been observed in association with RMSF include abdominal pain that mimics acute appendicitis (102), cholecystitis (103), or gastroenteritis; diarrhea; conjunctival suffusion; periorbital and peripheral edema (more common in children); calf pain; acute transient hearing loss; hepatomegaly; and splenomegaly (6,104).…”

“…Without treatment, RMSF progresses rapidly. Patients treated after the fifth day of illness are more likely to die than those treated earlier in the course of illness (9,18,74,75). The frequency of hospital admission, intensive care unit admission, and death increases with time from symptom onset to initiation of appropriate antibacterial treatment (18) ( Table 2).…”

“…The frequency of hospital admission, intensive care unit admission, and death increases with time from symptom onset to initiation of appropriate antibacterial treatment (18) ( Table 2). Delays in diagnosis and initiation of antirickettsial therapy have been associated with seeking health care early in the course of the illness (7,74), late-onset or absence of rash (6,18), and nonspecific or atypical early manifestations, such as gastrointestinal symptoms (18,98) or absence of headache (75). Epidemiologic factors associated with increased risk for death include disease that occurs early or late in the typical tick season (74) and the lack of a report of a tick bite (9,75,98).…”