Different diagnostic methods for detection of influenza epidemics

Area of Science:

• * Epidemiology
• * Virology
• * Public Health Surveillance

Background:

• * Community-based surveillance of influenza-like illness (ILI) combined with virological sampling is crucial for early detection of influenza activity.
• * The Portuguese national surveillance network has collected ILI data for seven years, providing a robust dataset for evaluation.

Purpose of the Study:

• * To evaluate the contribution of different diagnostic techniques for influenza detection in a community-based setting.
• * To compare the effectiveness of virus isolation, multiplex RT-PCR, enzyme-linked immunoassay (EIA), and complement fixation tests (CFTs).

Main Methods:

• * Analysis of clinical morbidity data and virological samples from 1685 ILI cases over a 7-year period.
• * Comparison of detection rates and timing for influenza virus using virus isolation, RT-PCR, EIA, and CFTs.

Main Results:

• * RT-PCR detected influenza in 43.6% of samples, EIA in 17.5%, and virus isolation in 5%.
• * RT-PCR demonstrated earlier detection of influenza and better correlation with ILI epidemic patterns compared to other methods.
• * Good correlation was observed between increased morbidity, sample collection, and influenza detection across all methods, though less pronounced for virus isolation and EIA.

Conclusions:

• * RT-PCR is a rapid, sensitive, and specific method for detecting influenza viruses in community-based surveillance.
• * RT-PCR is particularly valuable in systems where traditional virus culture methods are sub-optimal for timely influenza detection.