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Canada take notice: Antibiotics should be considered early for Rocky Mountain Spotted Fever (RMSF) in endemic areas even if classic findings are absent

Clin Infect Dis. 2015 Jun 1;60(11):1659-66. doi: 10.1093/cid/civ116. Epub 2015 Feb 19.

Risk factors for fatal outcome from rocky mountain spotted Fever in a highly endemic area-Arizona, 2002-2011.

Author information

  • 1Rickettsial Zoonoses Branch, Division of Vector-Borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases (NCEZID), Centers for Disease Control and Prevention (CDC), Atlanta, Georgia.
  • 2Indian Health Service Hospital, Arizona.
  • 3Poxvirus and Rabies Branch, Division of High-Consequence Pathogens and Pathogenicity, NCEZID.
  • 4Epidemic Intelligence Service, Division of Applied Public Health Training, Epidemiology Program Office, CDC, Atlanta, Georgia.
  • 5Bacterial Diseases Branch, Division of Vector-Borne Diseases, NCEZID, CDC, Fort Collins, Colorado.
  • 6Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh.
  • 7Department of Health and Human Services, Community B.
  • 8Division of Health Programs, Community A.
  • 9Bureau of Epidemiology and Disease Control, Division of Public Health Services, Arizona Department of Health Services, Phoenix.



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.


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.


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.


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.
Published by Oxford University Press on behalf of the Infectious Diseases Society of America 2015. This work is written by (a) US Government employee(s) and is in the public domain in the US.


American Indians; Rhipicephalus sanguineus; Rocky Mountain spotted fever; fatalities; tick-borne
[PubMed – in process]

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One Comment

  1. I have been encouraging people in southern Ontario to be tested for RMSF, due to symptoms prevelence. Being a Nurse and trained in the U.S. where RMSF was actively treated; and having had it myself, I am aware of symptomology.
    Every person that has been able to convince their doctors to run this test has come back with a IgG positive result; however, most doctors are interpreting as negative,( except for one doctor – so far).
    As doctors are not aware of the high mortality rate, nor very quick progession of this illness; many are presenting with early onset dementia and mobility issues. and not being treated.
    This is a problem which I have already extended to my MPP, who is currently working on it with the Minister of Health.
    RMSF is not only Dangerousit can be Lethal – but I feel that the first obstacle is making doctors aware of the fact that it ‘Does Exist” here in Ontario. This is a major problem – as many cannot obtain the test from their GP’s; and if they do – GP’s have no knowledge of this illness.
    I have recently had a GP tell me that a lab result of IgG 1:128 is negative; and this GP also stated that this information was given to her by Public Health. If that is the case, I believe that Public Health needs to be addressed with accurate information as well.

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