Table 1

BFP results as a proportion of reactive syphilis serological tests by HCV serostatus

	HCV antibody +	HCV antibody −	OR (95% CI)
All	1256	2410
RPR reactive	180 (14%)	174 (7%)	2.15 (1.7 to 2.7)
BFP	55	32
Of all reactive RPR	(31%)	(19%)	1.9 (1.1 to 3.1)
Of all syphilis tests	(4%)	(1%)	3.3 (2.1 to 5.1)
No history of IDU	378	2365
RPR reactive	58 (15%)	163 (7%)	2.5 (1.8 to 3.4)
BFP	14	31
Of all reactive RPR	(24%)	(19%)	NS
Of all syphilis tests	(4%)	(1%)	3.1 (1.6 to 5.9)
HIV seronegative	185	748
RPR reactive	21 (11%)	37 (5%)	2.5 (1.4 to 4.3)
BFP	10	7
Of all reactive RPR	(48%)	(19%)	3.9 (1.0 to 15.2)
Of all syphilis tests	(5%)	(1%)	6.0 (2.1 to 15.0)
HIV seronegative/no history of IDU	48	692
RPR reactive	9 (19%)	35 (5%)	4.3 (2.0 to 9.7)
BFP	3	6
Of all reactive RPR	(33%)	(17%)	NS
Of all syphilis tests	(6%)	(1%)	7.6 (1.9 to 12.5)

BFP, biological false positive; HCV, hepatitis C virus; IDU, intravenous drug use; NTST, non-treponemal serological test; OR, odds ratio; RPR, rapid plasma reagin.