Rocky Mountain spotted fever - Chem-Bio-Rad Suspicion
Rickettsia rickettsii, a gram-negative bacterium, is the causative agent of Rocky Mountain spotted fever (RMSF). The disease is spread by the bite of ixodid (hard) ticks. It is the most severe rickettsial illness of humans and is difficult to diagnose due to early nonspecific findings. Without treatment, the case fatality rate is 20%-30% with a median time to death of 8 days. Otherwise healthy adults and children have been known to die from the disease.
The disease is spread by ticks (the American dog and Rocky Mountain ticks) via a tick bite or by the crushing of a tick and transmittal of its fecal matter via a mucosal surface (eg, rubbing the eyes). RMSF is a misnomer; it is most commonly seen in the southeastern US, Texas, and Oklahoma, not in the Rocky Mountains. Over 90% of cases occur during April-September. The disease is more frequent in males; age-specific incidence is highest in children. Overall, the incidence of RMSF has been increasing from approximately 500 to 2,000 cases per year, but the case fatality rates (at least in the US) have been decreasing (attributed to enhanced recognition and early treatment).
Early clinical manifestations of RMSF include high fever, severe headache, myalgia, and nausea and vomiting. Later manifestations include rash, photophobia, confusion, ataxia, seizures, cough, dyspnea, arrhythmias, jaundice, and severe abdominal pain. Thrombocytopenia or hyponatremia may also be seen. A serious complication of RMSF is rhabdomyolysis. Long-term sequelae include CNS deficits and amputations.
RMSF can be prevented through the use of protective clothing and insect repellants and avoidance of tick areas and by conducting skin inspections after periods of outdoor activity.
RMSF is infectious as an aerosol, and if weaponized, that would be the most likely method of dispersal.
Classic triad of RMSF:
3) History of tick exposure in last 12 days
A77.0 – Spotted fever due to Rickettsia rickettsii
186772009 – Rocky Mountain spotted fever
- Meningococcemia typically occurs in the late winter to early spring with fever and rash appearing within 24 hours of infection. There is also marked lymphadenopathy.
- Measles typically occurs in the winter to spring and has associated symptoms of cough, coryza, conjunctivitis, and Koplik spots.
- Enteroviral infections typically occur in the summer to fall. The fever and rash often appear together. Sick contacts are common.
- Dengue fever, also known as "breakbone fever," has severe arthralgias.
- Vasculitis is marked by palpable purpura rather than petechiae.
- Drug eruptions will have a history of exposure.
- Secondary syphilis can also present with a palm and sole rash; occasionally, the rash imparts a rust-colored hue.
- Gonococcemia may present with asymmetric monoarticular arthritis and a pustular or petechial rash.
- Viral or bacterial enterocolitis presents with nausea and vomiting.
- Acute surgical abdomen has severe abdominal pain.
- Hepatitis presents with jaundice.
- Meningitis has prominent neurological signs.
- Idiopathic thrombocytopenic purpura (ITP) presents with a petechial rash.
- Thrombotic thrombocytopenic purpura (TTP) is characterized by fever, anemia, thrombocytopenia, renal impairment, and neurological deficits.