Pediatrics Maintenance of Certification

This patient has symptoms consistent with human monocytic ehrlichiosis, a tick-borne infection spread by Amblyomma americanum, or lone star ticks. The most commonly responsible organism, Ehrlichia chaffeensis, is a gram-negative, small, obligate intracellular bacterium. States with the highest incidence of human monocytic ehrlichiosis in recent years include New Hampshire, Vermont, Rhode Island, Delaware, Virginia, Kentucky, Tennessee, Missouri, Arkansas, Kansas, and Oklahoma. Most cases are seen predominantly in May through September, largely because there are higher numbers of lone star ticks during this time. Symptoms typically present between 2 and 21 days after the tick bite, although approximately one-fourth of patients have no history of a known tick bite. Fever, headache, and myalgias are the most frequently reported symptoms. The majority of children develop a rash, and about one-half develop organomegaly and lymphadenopathy. Altered mental status may also be present, and other symptoms may include nausea, vomiting, or abdominal pain. Laboratory evaluation often reveals leukopenia, thrombocytopenia, hyponatremia, and elevated transaminases, as this patient has. During the acute phase of illness, PCR amplification of Ehrlichia chaffeensis is the most sensitive diagnostic method, as antibody titers are often negative. However, a comparison of acute and convalescent IgG antibody titers by indirect immunofluorescence assay may be diagnostic if there is a fourfold rise.