TABLE 3.

Performance of multiplex quantitative PCR for detection of acute rickettsial infections in patients with acute febrile illness

Bacterium	Gene target	No. true positives	No. test positives	Sensitivitya	True negatives	Test negatives	Specificitya	PPVb	NPVb
Anaplasma phagocytophilum	msp2 (p44)	14	14	0.93	184	182	0.99	0.88	0.99
Ehrlichia chaffeensis	vlpt	45	38	0.84	154	151	0.98	0.93	0.96
Orientia tsutsugamushi	tsa56 (56-kDa surface antigen)	30	8	0.27	169	169	1.0	1.0	0.88
Spotted fever Rickettsia	ompA	20	5	0.25	176	173	0.98	0.63	0.92
Typhus group Rickettsia	17-kDa surface antigena	30	6	0.2	167	165	0.99	0.75	0.87

^aSensitivity is the proportion of true positives with a positive test result (test positive/all with disease = test positives plus false negatives); specificity is the proportion of true negatives (nondiseased) with a negative test result (test negative/all without disease = test negatives plus false positives).

^bPPV, positive predictive value; NPV, negative predictive value.