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PA Boards 102: Rocky Mountain Spotted Fever

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Rocky mountain spotted fever occurs from rickettsia rickettsii and is transmitted by the American Dog Tick. The incubation period is 2 to 14 days after being bitten by an infected tick (5-7 days on average). Signs and symptoms early in the course of the disease are non-specific and the characteristic rash doesn’t appear for 3-5 days into the illness. The rash is characteristic in most: starts at the ankles and wrists and moves centrally – includes the palms and soles. Up to 10% of patients NEVER develop a rash.

Initial symptoms include fever, nausea, headache, malaise, myalgias, and arthralgias. Severe disease can lead to death within 3-5 days.

This is a clinical diagnosis and treatment should not be made based on laboratory testing. Some abnormalities which may be noted include thrombocytopenia, hyponatremia, prolonged PT/PTT, and elevated LFTs. As the disease progresses the patient will have positive indirect fluorescent antibodies.

Do not wait for the rash to be present before initiating treatment – very common mistake. Treatment should be initiated within 5 days of disease to prevent progression and to reduce mortality.

All patients should be treated with doxycycline. This is first line for adults, children, and for pregnant women who are in their third trimester. Chloramphenicol can be used in the first two trimesters for mild disease only. Chloramphenicol is associated with gray syndrome in the newborn if used in the third trimester. If chloramphenicol is not available then doxycycline should be used.

Adults are treated with doxycycline 100mg BID (orally or intravenously). A loading dose of 200mg can be given to those with more severe disease. Children under 45 kg are treated with 2.2mg/kg/dose twice daily with a maximum dose of 200mg daily. Children over 45 kg are treated like adults.

Treatment is continued for 3 days after the patients fever subsides. Improvement in symptoms are typically seen after 48 hours.

The CDC states clinicians often avoid prescribing doxycycline to young children because of a warning that tooth staining may occur when used in children less than 8 years old. This is not the case. The CDC states that short courses of the antibiotic doxycycline can be used in children without causing tooth staining or weakening of tooth enamel. This is more true with the older tetracycline antibiotics – not so much for doxycycline.

Also, the child’s life is more important than the slight risk of tooth staining. This is the only antibiotic with proven efficacy in treating patients for all rickettsial diseases. Delaying treatment until after the 5th day increases the mortality rate to 23% (.3% when given before the 5th day).

There are different strains with varying degrees of virulence. Mortality ranges from 20% – 80% depending on the location.

Bottom line: start doxycycline as soon as you suspect the diagnosis of rocky mountain spotted fever – do not choose an alternative antibiotic because of age.