Rapid influenza tests unreliable for influenza A H1N1

A study published in Morbidity and Mortality Weekly Report reaffirms recommendations against using rapid test results alone to make infection control decisions during the current pandemic.

Staff members from Greenwich Hospital and the Connecticut Department of Public Health collected data on symptoms for 63 students from two schools in Greenwich, Conn. last May, after several students became ill.

Patients submitted nasopharyngeal washings for testing using a rapid influenza diagnostic test for influenza A and B and real-time reverse transcription-polymerase chain reaction (rRT-PCR) assay.

Forty-nine patients had infections with pandemic influenza A H1N1 confirmed by rRT-PCR. Compared with rRT-PCR, the sensitivity of the rapid test for detecting infection in patients with 2009 pandemic influenza A H1N1 was 47%, and the specificity was 86%. Researchers said results did not vary substantially by the presence or absence of CDC-defined influenza-like illness or by time from symptom onset to specimen acquisition. Negative tests did not accurately predict absence of infection, the researchers said. The negative predictive value was 32%.

The findings affirm CDC recommendations that rapid test results alone not be used to make infection control decisions, according to the researchers.

CDC. MMWR. 2009. 58;1029-1032.