Emerging Infectious Disease ISSN: 1080-6059

Rapid Influenza Antigen Test for Diagnosis of Pandemic (H1N1) 2009

Janice K. Louie

, Hugo Guevara, Erica Boston, Melissa Dahlke, Maria Nevarez, Tong Kong, Robert Schechter, Carol A. Glaser, and David P. Schnurr

Author affiliations: California Department of Public Health, Richmond, California, USA

Performance of rapid antigen test compared with PCR in the diagnosis of pandemic (H1N1) 2009*

Parameter	All specimens	Patient age <18 y†	Patient age >18 y†
No. rapid test positive, PCR positive	266	131	130
No. rapid test positive, PCR negative	49	19	28
No. rapid test negative, PCR positive	138	62	74
No. rapid test negative, PCR negative	250	78	166
Total no. tested	703	290	398
Prevalence of PCR positives in sample	0.57	0.67	0.51
Sensitivity	0.66	0.68	0.64
Specificity	0.84	0.80	0.86
Positive predictive value	0.84	0.87	0.82
Negative predictive value	0.64	0.56	0.69
Positive likelihood ratio (95% CI)	4.0 (3.1–5.2)	3.5 (2.3–5.3)	4.4 (3.1–6.3)
Posterior probability of positive test result (95% CI)	0.84 (0.81–0.88)	0.87 (0.82–0.91)	0.82 (0.76–0.87)
Negative likelihood ratio (95% CI)	0.41 (0.35–0.47)	0.40 (0.32–0.50)	0.42 (0.35–0.51)
Posterior probability of negative test result (95% CI)	0.36 (0.32–0.39)	0.44 (0.39–0.50)	0.31 (0.27–0.35)

*CI, confidence interval.
†Does not include results for 15 case-patients where age was not recorded.