Update on influenza diagnostics: lessons from the novel H1N1 influenza A pandemic

The menu of diagnostic tools that can be utilized to establish a diagnosis of influenza is extensive and includes classic virology techniques as well as new and emerging methods. This review of how the various existing diagnostic methods have been utilized, first in the context of a rapidly evolving outbreak of novel influenza virus and then during the different subsequent phases and waves of the pandemic, demonstrates the unique roles, advantages, and limitations of each of these methods. Rapid antigen tests were used extensively throughout the pandemic. Recognition of the low negative predictive values of these tests is important. Private laboratories with preexisting expertise, infrastructure, and resources for rapid development, validation, and implementation of laboratory-developed assays played an unprecedented role in helping to meet the diagnostic demands during the pandemic. FDA-cleared assays remain an important element of the diagnostic armamentarium during a pandemic, and a process must be developed with the FDA to allow manufacturers to modify these assays for detection of novel strains in a timely fashion. The need and role for subtyping of influenza viruses and antiviral susceptibility testing will likely depend on qualitative (circulating subtypes and their resistance patterns) and quantitative (relative prevalence) characterization of influenza viruses circulating during future epidemics and pandemics.