Reported Cases of Spotted Fever Rickettsioses Rarely Confirmed
Elevated IgG antibody titer was most common supportive lab evidence for probable cases
MONDAY, March 18, 2019 (HealthDay News) -- Only 1.0 percent of reported cases of spotted fever rickettsioses (SFR) meet the confirmed case definition, according to research published in the March 15 issue of the U.S. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.
Alison M. Binder, from the CDC in Atlanta, and colleagues examined supplementary case report forms to analyze the quality of laboratory data used to support the diagnosis of SFR cases with illness onset during 2010 to 2015.
The researchers found that only 1.0 percent of the 16,807 reported cases met the confirmed case definition and 99.0 percent met the probable case definition. For probable cases, the most common supportive laboratory evidence was elevated immunoglobulin G antibody titer by indirect immunofluorescence assay, which was reported for 88.8 percent of probable cases. Because antibodies to spotted fever group Rickettsia can persist for months or years following infection, a single antibody titer is unreliable for diagnosis of incident disease in the absence of a convalescent specimen.
"This analysis highlights the importance of collecting appropriately timed specimens for serologic confirmation and use of molecular diagnostic tests," the authors write.