History and exam

Key diagnostic factors

common

known recent tick exposure or bite

Present in 50% to 66% of patients.[14][15][16][17]​​​

triad of fever, rash, and history of tick exposure

Present in 45% to 67% of patients.[14]

triad of fever, rash, and headache

Present in 44% to 58% of patients.[14]

fever

Present in >95% of patients.[14] It is important to note that the clinical presentation of cases in Arizona may differ from the usual presentation, and many cases lack history of a fever.​[6]

rash

Present in >95% of children and 80% of adults. Usually not present in the first 3 days of illness in adults, but can appear after 1 to 2 days of illness in children. Usually maculopapular at first, but can begin with petechiae.[14][15] A petechial rash develops in 50% to 60% of patients, usually after 1 to 2 days of maculopapular rash.[14][15]​​​

The presence of a maculopapular or petechial rash markedly increases the likelihood of Rocky Mountain spotted fever; however, the absence of a rash does not exclude the diagnosis. [Figure caption and citation for the preceding image starts]: Child's right hand and wrist displaying the characteristic spotted rash of Rocky Mountain spotted feverCDC Image Library; used with permission [Citation ends].com.bmj.content.model.Caption@2806f6a5[Figure caption and citation for the preceding image starts]: Macular rash of early Rocky Mountain spotted feverFrom the collection of Dr Christopher A. Ohl [Citation ends].com.bmj.content.model.Caption@320ffe86[Figure caption and citation for the preceding image starts]: Maculopapular and petechial rash of Rocky Mountain spotted feverFrom the collection of Dr Christopher A. Ohl [Citation ends].com.bmj.content.model.Caption@f4bce6a

headache

Present in 60% to 90% of patients.[14][15]

nausea/vomiting

Present in 60% to 75% of patients.[14][15]

myalgia

Myalgia and malaise are usually present.

uncommon

altered mental status

Present in approximately 30% of patients.[14][15]

Other diagnostic factors

common

abdominal pain

Present in approximately 50% of patients.[14][15] ​

uncommon

residence in or recent exposure to rural area

Reported in 31% to 34% of children and 44% of adults.[14][15]

diarrhoea

Present in approximately 20% of patients.[14][15]

conjunctivitis

Present in approximately 30% of patients.[14][15]

lymphadenopathy

Present in approximately 30% of patients.[14][15]

peripheral oedema

Present in approximately 20% of patients.[14][15]

meningismus

Present in approximately 18% of patients.[14][15]

splenomegaly

Present in approximately 15% of patients.[14][15]

hepatomegaly

Present in approximately 15% of patients.[14][15]

jaundice

Present in approximately 10% of patients.[14][15]

seizures

Present in approximately 10% of patients.[14][15]

shock

Present in approximately 10% of patients.[14][15]

coma

Present in approximately 10% of patients.[14][15]

Risk factors

strong

illness onset in spring or summer

Ninety percent of US cases present between 1 April and 30 September.[2][14]

returned travellers from an endemic area

Cases may present in travellers returning from outdoor activities in an endemic region.[1][10]

recent (within 2 weeks) outdoor exposure

A detailed history of recent recreational or occupational outdoor activities may reveal potential tick exposures that were unknown to the patient.

In endemic areas, such as northern Mexico or southwestern US, patients may be exposed to ticks in their own gardens. A recent camping or fishing trip suggests tick exposure, but most patients lack such historical clues.[14]

weak

known antecedent tick bite

Because people are usually unaware of tick bites, only about one half of affected patients recall removing an attached tick in the 2 weeks preceding the illness onset.​​[14][15][16][17]​​​

exposure to dogs or pets that spend time outdoors

Dogs and pets that spend time outdoors are at risk of tick bites and getting infected.

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