TABLE 1.

Summary of patient sera used in this study^a

Panel (n)b	Diagnosisc	No. of samples
		Virus infectedd	Serology		All negativeg
			IgMe	HIf
1 (80)h	Confirmed DEN	30	42	43	8
2 (82)	Confirmed DEN	18	60	54	0
3 (39)h	Confirmed non-DEN	0	0	0	39

^aBoth acute-phase (early symptomatic phase) as well as convalescent-phase (1 to 2 weeks later) samples were collected; the data shown are for the acute-phase sera. (For details, see the supplemental material.)

^bEighty patients for whom paired acute- and convalescent-phase sera could be collected were placed in panel 1. Eighty-two DEN virus infection-confirmed patients for whom single acute-phase sera were available were assigned to panel 2. Panel 3 consisted of 39 acute-phase febrile patients confirmed to be non-DEN cases. Of these, paired sera were available from 8 patients, while single acute-phase samples were collected from the remaining 31.

^cBased on the presence of DEN virus RNA and/or a positive IgM and/or HI test in conjunction with clinical presentation.

^dDEN virus RNA in sera was detected by RT-PCR; infectious virus could be isolated successfully from several RT-PCR-positive sera.

^eAnti-DEN virus IgM antibodies were detected using a commercial MAC-ELISA kit (Focus Diagnostics).

^fLaboratory confirmation of DEN infection was defined by positive detection of a ≥4-fold rise in anti-DEN virus IgG antibody titers in paired sera; HI titers of <20 were identified as non-DEN cases.

^gSera that tested negative by RT-PCR, virus isolation, MAC-ELISA, and HI assay.

^hConvalescent-phase sera were obtained (1 to 2 weeks after collection of acute-phase sera) from all 80 patients in panel 1 and from 8 patients in panel 3. All panel 1 convalescent-phase sera were IgM⁺ HI⁺, while all 8 convalescent-phase panel 3 sera were IgM⁻ HI⁻.