TABLE 2.

Sensitivity and specificity of the KCDC IgM/IgG IFA^a

Cutoff	IFA	Sensitivity, % (95% CI)	Specificity, % (95% CI)	+LR (95% CI)	−LR (95% CI)
≥0	IgM	100.00 (96.3–100.0)	0.00 (0.0–2.0)	1.00 (1.0–1.0)
	IgG	100.00 (96.3–100.0)	0.00 (0.0–2.0)	1.00 (1.0–1.0)
16	IgM	55.67 (45.2–64.8)	94.76 (90.6–97.5)	10.63 (5.7–19.9)	0.48 (0.4–0.6)
	IgG	51.55 (41.2–61.8)	85.86 (80.1–90.5)	3.65 (2.6–5.9)	0.56 (0.5–0.7)
32	IgM	52.58 (42.2–62.8)	97.38 (94.0–99.1)	20.08 (8.1–47.8)	0.49 (0.4–0.6)
	IgG	48.45 (38.2–58.8)	88.48 (83.1–92.6)	4.21 (2.8–7.3)	0.58 (0.5–0.7)
64	IgM	48.45 (38.2–58.8)	98.43 (95.5–99.7)	30.85 (9.6–94.6)	0.52 (0.4–0.7)
	IgG	47.42 (37.2–57.8)	90.58 (85.5–94.3)	5.03 (3.2–8.7)	0.58 (0.5–0.7)
128	IgM	47.42 (37.2–57.8)	100.00 (98.1–100.0)		0.53 (0.5–0.7)
	IgG	44.33 (34.2–54.8)	94.24 (89.9–97.1)	7.70 (4.4–16.0)	0.59 (0.5–0.7)
256	IgM	32.99 (23.8–43.3)	100.00 (98.1–100.0)		0.67 (0.6–0.8)
	IgG	42.27 (32.3–52.7)	96.34 (92.6–98.5)	11.53 (5.9–30.4)	0.60 (0.5–0.7)
512	IgM	24.74 (16.5–34.5)	100.00 (98.1–100.0)		0.75 (0.7–0.8)
	IgG	38.14 (28.5–48.6)	97.38 (94.0–99.1)	14.57 (5.9–35.7)	0.64 (0.5–0.7)
1,024	IgM	17.53 (10.6–26.6)	100.00 (98.1–100.0)		0.82 (0.8–0.9)
	IgG	31.96 (22.9–42.2)	98.95 (96.3–99.9)	30.52 (7.4–124.2)	0.69 (0.6–0.8)
2,048	IgM	7.22 (3.0–14.3)	100.00 (98.1–100.0)		0.90 (0.9–1.0)
	IgG	26.80 (18.3–36.8)	99.48 (97.1–100.0)	51.20 (7.4–369.7)	0.74 (0.6–0.8)
4,096	IgM	3.1 (0.6–8.8)	100.00 (98.1–100.0)		0.97 (0.9–1.0)
	IgG	16.49 (13.9–29.4)	99.46 (97.0–100.0)	38.82 (5.3–283.1)	0.80 (0.7–0.9)
>4,096	IgM	1.03 (0.0–5.6)	100.00 (98.1–100.0)		1.00 (1.0–1.0)
	IgG	0.00 (0.0–3.7)	100.00 (98.1–100.0)		1.00

^aIFA, indirect immunofluorescence assay; KCDC, Korea Centers for Disease Control and Prevention; 95% CI, 95% confidence interval; +LR, positive likelihood ratio; −LR, negative likelihood ratio. Values in boldface indicate the results were obtained at cutoff values of ≥1:16 for IgM and ≥1:256 for IgG, which are the reference cutoff values for positivity.