Evaluation of single and double-locus real-time PCR assays for methicillin-resistant Staphylococcus aureus (MRSA) surveillance

Table 2 Clinical samples results of single and double-locus detection assays

	Real Time PCR results
Conventional culture identification (n = 338)	Huletsky's[8] single-locus detection^a		Reischl's[5] double-locus detection^b				Combined results^c
	SCC:orfX+ (MRSA)	SCC:orfX- (other)	Sa442+ mec+ (MRSA)	Sa442+ mec- (MSSA)	Sa442- mec+ (non S.A oxaR)	Sa442- mec- (other)	MRSA^d	Not MRSA^e
MRSA (n = 219)	203	16	218	1	---	---	202	17^f
MSSA (n = 90)	13	77	(44+2)^g	35	---	9	1^h	89ⁱ
MR-CoNS (n = 16)	---	16	---	---	16	---		16
MS-CoNS (n = 8)	---	8	---	---	---	8		8
non-Staph. (n = 5)	---	5				5		5

^a sensitivity = 92.7%, specificity = 89.1%, Positive predictive value = 93.4%, Negative predicted value = 86.9%,
^b sensitivity = 99.5%, specificity = 61.3%, Positive predictive value = 82.6%, Negative predicted value = 98.6%
^c sensitivity = 92.2%, specificity = 99.2%, Positive predictive value = 99.5%, Negative predicted value = 87.4%
^d MRSA = SCC:orfX positive, Sa442 positive, mec positive
^e Not MRSA = all other results.
^f 16 SCC:orfX negative, Sa442 positive, mec positive and 1 oxacillin-resistant MSSA (SCC:orfX positive, Sa442 positive mec negative) classified as MRSA by culture methods.
^g 44 were MSSA mixed with MR-CoNS, 2 were oxacillin-susceptible MRSA classified as MSSA by culture methods.
^h 1 SCC:orfX positive, Sa442 positive, mec positive originated from a mixture of SCC:orfX positive, Sa442 positive, mec negative MSSA and mec positive MR-CoNS
ⁱ 9 SCC:orfX negative, Sa442 negative, mec negative; 2 SCC:orfX negative, Sa442 positive, mec positive; 22 SCC:orfX negative, Sa442 positive, mec negative; 13 SCC:orfX positive, Sa442 positive, mec negative MSSA's and 43 SCC:orfX negative, Sa442 positive, mec

ISSN: 1756-0500