Table 5.

Frequency of laboratory methods used in the diagnosis of probable SFG rickettsiosis in the United States, 2008–2012 (CRFs)

Methodology	Number of probable cases	Frequency among probable cases (N = 10,217)
Fourfold IgG by IFA*	265	2.6%
Less than 4-fold rise in IgG among paired samples by IFA	790	7.7%
Single elevated IgG by IFA	7,335	71.8%
IFA IgM	1,590	15.6%
ELISA tests	1,903	18.6%
Agglutination	9	0.1%

CRFs = case report forms; ELISA = enzyme-linked immunosorbent assay; IFA = indirect immunofluorescence assay; IgG = immunoglobulin G; IgM = immunoglobulin M; SFG = spotted fever group.

Cases may meet one or more laboratory criteria and does not include cases where test type was not specified, therefore, representative of minimum values.

^*Does not meet timing criteria for confirmatory laboratory evidence.