The "Timeless" use of Influenza-like Illness Criteria for influenza Detection in the Tropics.

Aung, Aung H; Lye, David C; Cui, Lin; Ooi, Chee K; Chow, Angela Lp

OBJECTIVE We assessed the performance of influenza-like illness (ILI) case definitions by the Centers for Disease Control and Prevention (CDC), European Centers for Disease Control and Prevention (ECDC), and World Health Organization (WHO) in the tropics where the seasonal patterns of respiratory viruses in acute upper respiratory tract infections (AURTIs) are ill defined. METHODS Clinical data and samples for respiratory multiplex PCR test were collected from 717 consecutive patients attending for uncomplicated AURTI at a busy emergency department in Singapore, 2016-2018. RESULTS Influenza (20.6%), rhinoviruses (14.4%), and coronaviruses (3.6%) were the most common viral pathogens. Biannual peaks with year-round activity was identified for Influenza. Although higher rhinoviruses activity was observed in inter-influenza seasonal periods, rhinoviruses and coronaviruses circulated year-round without distinct seasonal patterns. During high influenza activity months, the CDC's and WHO's ILI case definitions had moderate-to-high positive likelihood ratios (LR + s) of 3.8-6.8 and 4.5-10.7 respectively for ruling in influenza. During other months, they had moderately high LR + s of 3.3-3.8 and 3.9-4.6 for clinically diagnosing influenza infection. The ILI case definitions had high specificities (77.2-85.4%) for rhinoviruses and coronaviruses. CONCLUSION The CDC and WHO ILI case definitions can be applied to clinically diagnose influenza in the tropics, regardless of the time of the year.