Table 2.

Proportion of influenza A virus-positive samples detected, sensitivity, negative predictive value, and kappa statistic for single swabs or two swabs considered together

Swab type or result	No. of influenza A virus-positive swabs/no. of swabs (%)	No. of influenza A virus-positive samples not detected by:		Sensitivityc (95% confidence interval)		Negative predictive valued (95% confidence interval)		Kappa statistic (standard error)
		Single swab (n = 53)a	Two swabsb (n = 53)	Single swab	Two swabs	Single swab	Two swabs
Any swab	53/290 (18)
Consistent across all swabs	33/53 (62)
Not consistent across all swabs	20/53 (38)
Results for one swab typee
NP only	46/290 (16)	7 (13)		0.87 (0.75–0.95)		0.97 (0.94–0.99)
NS only	40/290 (14)	13 (25)		0.75 (0.62–0.86)		0.95 (0.91–0.97)
OP only	46/290 (16)	7 (13)		0.87 (0.75–0.95)		0.97 (0.94–0.99)
Results for two swab typesf
NP or NS	50/290 (17)		3 (6)		0.94 (0.84–0.99)		0.99 (0.96–1.00)	0.81 (0.71–0.91)
NP or OP	51/290 (18)		2 (4)		0.96 (0.87–1.00)		0.99 (0.97–1.00)	0.87 (0.79–0.95)
OP or NS	51/290 (18)		2 (4)		0.96 (0.87–1.00)		0.99 (0.97–1.00)	0.78 (0.68–0.88)

^an is the number of influenza A virus-positive swabs by any swab result.

^bConsidering the results for two swabs together.

^cSensitivity is the number of swabs identified as influenza A virus positive by single swab or swab combination/number of influenza A virus-positive swabs by any swab result.

^dNegative predictive value is the number of consistently negative swab results/number of influenza A virus-negative results identified by single swab or swab combination.

^eResults for one swab type only considered. NP, nasopharyngeal; NS, nasal; OP, oropharyngeal.

^fResults from both swabs tested separately considered.