Clinical Presentation, Risk Factors, and Comparison of Laboratory Diagnostics for Seasonal Influenza Virus among Cambodians from 2007-2020

Abstract Background Despite its global significance, challenges associated with understanding the epidemiology and accurately detecting, measuring, and characterizing the true burden of seasonal influenza remain in many resource-poor settings. Methods A prospective observational study was conducted in Cambodia at 28 health facilities between 2007 and 2020 utilizing passive surveillance data of patients presenting with acute undifferentiated febrile illness (AUFI) to describe the prevalence of Influenza A and B and characterize associated risk factors and symptoms using a questionnaire. A comparison of rapid influenza diagnostic tests (RIDT) and real-time reverse transcription-polymerase chain reaction (rRT-PCR) results was also conducted. Results Of 30,586 total participants, 5,634 (18.4%) tested positive for either Influenza A or B, with 3,557 (11.6%) positive for Influenza A and 2,288 (7.5%) for Influenza B during the study. Influenza A and B were strongly associated with the rainy season (OR=2.30, p<0.001) and among participants from urban areas (OR=1.45, p<0.001). Analysis of individual symptoms identified cough (OR=2.8, p<0.001), chills (OR=1.4 p<0.001), and sore throat (OR=1.4, p<0.001) as having the strongest positive associations with influenza among patients with AUFI. Analysis comparing RIDTs and rRT-PCR calculated an overall sensitivity of rapid tests as 0.492 (95% CI 0.479, 0.505) and a specificity of 0.993 (95% CI 0.992, 0.994) for both Influenza type A and B. Conclusions Findings from this 14-year study include describing the epidemiology of seasonal influenza over a prolonged time-period, identifying key risk factors and clinical symptoms associated with infection, and demonstrated the poor sensitivity of RIDTs in Cambodia.