The Naval Health Research Center serves as the Navy hub for the Department of Defense´s Global Emerging Infections Surveillance and Response System (GEIS), in which it monitors influenza-like illness among recruit trainees of all military services, military dependents, and crew members of large Navy ships (population, >1000). The center works in collaboration with the Border Infectious Disease Surveillance Project of the Centers for Disease Control and Prevention (CDC), which monitors populations located on the border between California and Mexico. The first two human cases of novel swine-origin influenza A (H1N1) virus (S-OIV), known as swine flu, in the United States were detected through these programs.¹ In the first case, an untypable influenza A strain was identified at a surveillance site of the Naval Health Research Center by a new diagnostic device. The test results were forwarded per protocol to the study reference laboratory for polymerase-chain-reaction (PCR) confirmation and were subsequently forwarded to the CDC for identification by sequencing. In the second case, a sample that was obtained at a border surveillance site was found to contain an untypable influenza A strain on PCR testing at the center. Further characterization by PCR assay and electrospray ionization mass spectrometry indicated a swine-origin virus, and sequence data that were sent to the CDC revealed that the viruses in the two samples were identical. In response, surveillance activities of all programs were enhanced to include increased sampling rates, more clinical sites, decreased turnaround time in the laboratory, and rapid influenza testing with the use of QuickVue Influenza A+B (Quidel).

From April 20 through May 30, 2009, the center processed 3066 specimens with the use of a real-time reverse-transcriptase–PCR (RT-PCR) assay,² which revealed 273 confirmed cases of S-OIV (8.9%), 18 cases of H1N1 seasonal influenza (0.6%), and 31 cases of H3N2 influenza (1.0%) (Figure 1). All suspected cases of S-OIV were confirmed with the use of the CDC´s S-OIV assay.² All specimens were collected from patients with influenza-like illness who met the CDC´s guidelines for screening. Rapid-test results for 767 patients during this influenza season were available for comparison and were positive for 20 of 39 patients who had positive results for S-OIV on RT-PCR assay (sensitivity, 51%; 95% confidence interval [CI], 35 to 67), for 12 of 19 patients who had positive results for H1N1 seasonal influenza on RT-PCR (sensitivity, 63%; 95% CI, 39 to 82), and for 6 of 19 of patients who had positive results for H3N2 influenza on RT-PCR (sensitivity, 31%; 95% CI, 14 to 57). The specificity of the test, as compared with that of RT-PCR, was 99% in all cases.