Comparison of diagnostic test performance in a population of high risk young adults versus a general population presenting with influenza

Background: Upper respiratory tract infection (URI) is a well-documented cause of morbidity, extra expense and lost training time among basic military trainees (BMTs). Objectives: The goal of this study is to better understand how influenza diagnostic tests perform in the BMT population, and how this performance differs from the general population. Study design: Laboratory test data was collected in a prospective study that enrolled Department of Defense beneficiaries presenting to medical facilities in San Antonio, TX with URI symptoms between January 2005 and March 2011. Three laboratory tests for influenza were performed during the study period: polymerase chain reaction (PCR), enzyme immunoassay (EIA), and viral culture. Patients were grouped into BMT and non-BMT populations and the tests from each of these populations were compared for statistical differences. Similar comparisons were made with various sub-groups to include: influenza A versus influenza B, and influenza A subtypes: (H1N1) versus (H3N2) versus (H1N1)pdm09. Results: Among 4448 participants enrolled, 466 (10.5%) tested positive for influenza. Sensitivity of viral culture differed between BMTs and non-BMTs: 63% versus 41% (p< 0.01). There was no difference in the sensitivity of PCR or EIA between the two populations. The sensitivities of viral culture, EIA and PCR were higher in those infected with influenza A than in those infected with influenza B. The sensitivity of viral culture was significantly higher in (H1N1)pdm09 subtype cases. Conclusions: Viral culture performed better in BMTs than in non-BMTs. These differences are likely attributable to the younger age of the BMTs.