A validation study comparing the sensitivity and specificity of the new Dr. KSU H1N1 RT-PCR kit with real-time RT-PCR for diagnosing influenza A (H1N1).

BACKGROUND AND OBJECTIVES: A new test (Dr. KSU H1N1 RT-PCR kit) was recently developed to provide a less expensive alternative to real-time reverse transcriptase-polymerase chain reaction (RT-PCR). We report the findings of a validation study designed to assess the diagnostic accuracy, including sensitivity and specificity, of the new kit, as compared to real-time RT-PCR.

DESIGN AND SETTING: Cross-sectional validation study conducted from 18-22 November 2009 at a primary care clinic for H1N1 at a tertiary care teaching hospital in Riyadh.

PATIENTS AND METHODS: Nasopharyngeal swab samples and data on socio-demographic characteristics and symptoms were collected from 186 patients. Swab samples were sent to the laboratory for testing with both real-time RT-PCR and the new Dr. KSU H1N1 RT-PCR kit. We measured the sensitivity and specificity of the new test across the entire sample size and investigated how these values were affected by patient socio-demographic characteristics and symptoms.

RESULTS: The outcomes of the two tests were highly correlated (kappa=0.85; P<.0001). The sensitivity and specificity of the new test were 99.11% and 83.78%, respectively. The sensitivity of the new test was affected only minimally (96%-100%) by patient characteristics and number of symptoms. On the other hand, the specificity of the new test varied depending on how soon patients were tested after onset of symptoms (100% specificity when swabs were taken on the first day of the symptoms, decreasing to 75% when swabs were taken on or after the third day). The specificity of the new test also increased with increasing body temperature.

CONCLUSION: The new test seems to provide a cost-effective alternative to real-time RT-PCR for diagnosing H1N1 influenza. However, further testing may be needed to verify the efficacy of the test in different settings and communities.