Laboratory test performance in young adults during influenza outbreaks at World Youth Day 2008

Background: The performance of influenza laboratory diagnostics in young adults and in the setting of outbreaks during mass gatherings has not been well studied. Objectives: We compare the performance of point-of-care tests (POCTs) and immunofluorescence assays (IFAs) with nucleic acid tests (NATs) and viral culture in pilgrims attending influenza clinics established during a large influenza outbreak (World Youth Day, Sydney, Australia, 2008) to assess their performance under the real-life pressures of a mass influenza outbreak. Study design: Patients with an influenza-like illness (ILI) underwent respiratory specimen sampling. Combined deep nares and throat swabs were collected for POCT by trained or untrained clinic staff; type-specific IFA; NAT and viral culture. Laboratory-confirmed influenza occurred if viral culture and/or NAT were positive; the performance of laboratory tests was calculated against this 'gold standard'. Results: A total of 230 samples were collected from 227 patients (median age, 20 years; interquartile range, 18-28 years), with 95 samples (41.3%) having laboratory-confirmed influenza infection (influenza A, 57; influenza B, 38). IFA and POCT sensitivities were 74.5% and 55%, respectively. Four of 51 (8%) culture-positive specimens were negative by NAT, and several errors in influenza virus typing occurred with IFA, POCT and NAT. A non-significant trend towards better POCT performance with increased operator training was demonstrated. Conclusion: Different environments, patient populations, operator experience, laboratory access and practicalities associated with performing tests during mass influenza outbreaks may affect performance of influenza-specific laboratory tests.