Table 1.

Non-treponemal and treponemal reactivities by the immuno-chromatographic test TDR DPP^® Syphilis Screen & Confirm Assay (Chembio Diagnostics Systems Inc., Medford, NY, USA)

	Cameroonian black	French black	French caucasian	Pc
n	103	104	51
Nontreponemal reactivity (n; %)
Reference serology, RPR a	0 (0.0)	0 (0.0)	0 (0.0)
Dual rapid test, nontreponemal line	24 (23.3)	13 (12.5)	1 (1.9)
Cameroonian Black versus French Black				<0.05
Cameroonian Black versus French Caucasian				<0.0004
French Black versus French Caucasian				<0.04
Treponemal reactivity (n; %)
Reference serology, IgG+IgM ELISAb	0 (0.0)	0 (0.0)	0 (0.0)
Dual rapid test, treponemal line	10 (9.7)	2 (1.9)	0 (0.0)
Cameroonian Black versus French Black				<0.02
Cameroonian Black versus French Caucasian				<0.04
French Black versus French Caucasian				NS
Indeterminate syphilis reactivities (n; %)d	34 (33.0)	15 (14.4)	1 (1.9)
Cameroonian Black versus French Black				<0.002
Cameroonian Black versus French Caucasian				<0.05
French Black versus French Caucasian				<0.04
Active syphilis false positivity (n; %)e	9 (8.7)	2 (1.9)	0 (0.0)
Cameroonian Black versus French Black				<0.04
Cameroonian Black versus French Caucasian				<0.04
French Black versus French Caucasian				NS

^aThe reference serology for non-treponemal line was the Rapid Plasma Reagin test (Arlington Scientific Inc., Spingville, Utah, USA); sera whose RPR titers were ≥ 1:2 were considered as positive;

^bThe reference serology for the treponemal line was the indirect ELISA for Treponema pallidum-specific IgG and IgM antibodies directed to 15-, 17-, and 47-kDa recombinant proteins as antigens (DiaSorin, Vercelli, Italy);

^cStatistical analyses were accrued out using Fisher exact test using GraphPad Prims software (version 5, La Jolla, CA, USA);

^dIndeterminate syphilis reactivities was defined as one or two bands by the immune-chromatographic dual test TDR DPP^® Syphilis Screen & Confirm Assay ;

^eActive syphilis false positivity was defined as two positive bands by the immune-chromatographic dual test TDR DPP^® Syphilis Screen & Confirm Assay.

n: Number; NS: Not significant