Diagnosis of West Nile virus infections: Evaluation of different laboratory methods

Table 1 Characteristics of patients with West Nile virus infection included in the study

Characteristic	Subcategory	n (%)1
Sex	Male	35 (56.4)
	Female	27 (43.6)
Age in median years (IQR)		68 (58-76)
Clinical diagnosis	Febrile headache	2 (3.2)
	Meningitis	36 (58.1)
	Meningoencephalitis	20 (32.3)
	Meningoencephalomyelitis	2 (3.2)
	Polyradiculoneuritis	2 (3.2)

¹Unless otherwise indicated. IQR: Interquartile range.

Table 2 Laboratory tests used for the diagnosis of West Nile virus infection

Method	Manufacturer/Protocol	Reference values
RT-PCR	FP: AAG TTG AGT AGA CGG TGC TG; RP: AGA CGG TTC TGA GGG CTT AC; Probe: FAM-CAA CCC CAG GAG GAC TGG-TAMRA
IgM ELISA	Euroimmun, Lübeck, Germany	Ratio < 0.8 negative; 0.8-1.1 borderline; > 0.1 positive
IgG ELISA	Euroimmun, Lübeck, Germany	RU/mL < 16 negative, 16-22 borderline; > 22 positive
IgG avidity	Euroimmun, Lübeck, Germany	AI < 40% low; 40%-60% borderline; > 60% high
VNT	In house	Titer ≥ 10 positive

AI: Avidity index; ELISA: enzyme immunoassay; IgG: Immunoglobulin G; IgM: Immunoglobulin M; RT-PCR: Reverse transcription-polymerase chain reaction; RU: Relative units; VNT: Virus neutralization test.

Table 3 Reverse transcription-polymerase chain reaction positive detection rates in cerebrospinal fluid and urine samples, n (%)

Days after symptoms onset	WNV RT-PCR CSF		WNV RT-PCR Urine
	Tested	Positive	Tested	Positive
≤ 7	22 (35.5)	8 (36.4)	17 (30.9)	5 (29.4)
8–14	32 (51.6)	10 (31.2)	30 (54.6)	20 (66.6)
≥ 15	8 (12.9)	2 (25.0)	8 (14.5)	5 (62.5)
Total	62 (100)	20 (32.2)	55 (100)	30 (54.4)

Data are n (%). CSF: Cerebrospinal fluid; WNV: West Nile virus; RT-PCR: Reverse transcription-polymerase chain reaction.

Table 4 Positive detection rate of West Nile virus antibodies in serum samples according to sampling time, n (%)

Days after symptoms onset	Tested	WNV IgM antibodies		WNV IgG antibodies
		Positive	Borderline	Positive	Borderline
≤ 7	32 (33.7)	27 (84.3)	0 (0)	3 (9.3)	2 (6.2)
8 – 14	38 (40.0)	38 (100)	0 (0)	27 (71.1)	5 (13.1)
≥ 15	25 (26.3)	25 (100)	0 (0)	25 (100)	0 (0)
Total	95 (100)	90 (94.7)	0 (0)	55 (57.8)	7 (7.3)

Data are n (%). IgG: Immunoglobulin G; IgM: Immunoglobulin M; WNV: West Nile virus.

Table 5 Positive detection rate of West Nile virus antibodies in cerebrospinal fluid samples according to sampling time, n (%)

		WNV IgM antibodies		WNV IgG antibodies
Days after symptoms onset	Tested	Positive	Borderline	Positive	Borderline
≤ 7	32 (51.6)	20 (62.5)	1 (3.1)	9 (28.1)	2 (6.2)
8–14	23 (37.1)	17 (73.9)	0 (0)	6 (26.1)	1 (4.3)
≥ 15	7 (11.3)	7 (100)	0 (0)	4 (57.1)	0 (0)
Total	62 (100)	44 (70.9)	1 (1.6)	19 (30.6)	3 (4.8)

Data are n (%). IgG: Immunoglobulin G; IgM: Immunoglobulin M; WNV: West Nile virus.

Table 6 Immunoglobulin G avidity in asymptomatic West Nile virus seropositive individuals

Serology result	IgG avidity index
	Low	Borderline	High
IgM/IgG positive, n = 10	1 (10.0)	1 (10.0)	8 (80.0)
IgM negative/IgG positive, n = 12	1 (8.3)	0 (0)	11 (91.7)
Total, n = 22	2 (9.1)	1 (4.5)	19 (84.6)

Data are n (%). IgG: Immunoglobulin G; IgM: Immunoglobulin M.