The three fatalities observed in a retrospective analysis of six cases of Rocky Mountain spotted fever (RMSF) in children were associated with either a delayed diagnosis pending laboratory findings or delayed antirickettsia treatment.

“The fact that all fatal cases died before the convalescent period emphasizes that diagnosis should be based on clinical findings instead of RMSF serologic and histologic testing,” wrote the authors of a study published online in Pediatric Dermatology ( 2016 Dec 19. doi: 10.1111/pde.13053 ).

Rechelle Tull of the department of dermatology, Wake Forest University, Winston-Salem, N.C., and her colleagues conducted a retrospective review of 3,912 inpatient dermatology consultations over a period of 10 years at a tertiary care center, and identified 6 patients aged 22 months to 2 years (mean, 5.1 years) diagnosed with RMSF. The patients were evaluated in the months of April, May, and June, and three of the six patients infected with the vector-borne obligate intracellular bacterium, Rickettsia rickettsii, had died within 4 days of hospitalization, according to the authors.

Two of the fatal cases involved delayed antirickettsial therapy after the patients were misdiagnosed with group A streptococcus. None of the six children were initially evaluated for R. rickettsii; they averaged three encounters with their clinician before being admitted for acute inpatient care where they received intravenous doxycycline after nearly a week of symptoms.

“All fatal cases were complicated by neurologic manifestations, including seizures, obtundation, and uncal herniation,” a finding that is consistent with the literature, the authors said.

Although the high fatality rate might be the result of the small study size, Ms. Tull and her coinvestigators concluded that the disease should be considered in all differential diagnoses for children who present with a fever and rash during the summer months in endemic areas, particularly since pediatric cases of the disease are associated with poorer outcomes than in adult cases.

Given that RMSF often remains subclinical in its early stages, and typically presents with nonspecific symptoms of fever, rash, headache, and abdominal pain when it does emerge, physicians might be tempted to defer treatment until after serologic and histologic results are in, as is the standard method. Concerns over doxycycline’s tendency to stain teeth and cause enamel hypoplasia are also common. However, empirical administration could mean the difference between life and death, since treatment within the first 5 days following infection is associated with better outcomes – an algorithm complicated by the fact that symptoms caused by R. rickettsii have been known to take as long as 21 days to appear.

In the study, Ms. Tull and her colleagues found that the average time between exposure to the tick and the onset of symptoms was 6.6 days (range, 1-21 days).

Currently, there are no diagnostic tests “that reliably diagnose RMSF during the first 7 days of illness,” and most patients “do not develop detectable antibodies until the second week of illness,” the investigators reported. Even then, sensitivity of indirect fluorescent antibody serum testing after the second week of illness is only between 86% and 94%, they noted. Further, the sensitivity of immunohistochemical (IHC) tissue staining has been reported at 70%, and false-negative IHC results are common in acute disease when antibody response is harder to detect.

Ms. Tull and her colleagues found that five of the six patients in their study had negative IHC testing; two of the six had positive serum antibody titers. For this reason, they concluded that Rocky Mountain spotted fever diagnosis should be based on “clinical history, examination, and laboratory abnormalities” rather than laboratory testing, and urged that “prompt treatment should be instituted empirically.”

The authors did not have any relevant financial disclosures.

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