Are atypical lymphocytes present with viral influenza-like illnesses (ILIs) in hospitalized adults?

The purpose of this investigation was to determine if atypical lymphocytes were of diagnostic value in viral influenza-like illnesses (ILIs) in hospitalized adults during the influenza season. Are atypical lymphocytes present with viral ILIs in hospitalized adults? During the influenza season, hospitals are inundated with influenza and viral ILIs, e.g., human parainfluenza virus-3 (HPIV-3). Without specific testing, clinically, it is difficult to differentiate influenza from ILIs, and surrogate influenza markers have been used for this purpose, e.g., relative lymphopenia. The diagnostic significance of atypical lymphocytes with ILIs is not known. We retrospectively reviewed the charts of 35 adults admitted with pneumonia due to viral ILI. The diagnosis of 14 patients was by respiratory virus polymerase chain reaction (PCR). During the 2015 influenza A season with ILIs, atypical lymphocytes were not present in influenza A (H₃N₂) patients but atypical lymphocytes were present in some ILIs, particularly HPIV-3. With viral ILIs, atypical lymphocytes should suggest a non-influenza viral diagnosis.