Beyond the Routine Influenza Surveillance

Choi, Sang-Ho

Influenza surveillance systems have been developed to monitor antigenic changes in influenza viruses, guide the selection of annual influenza vaccine strains, and provide viral samples for vaccine production [1] . Subsequently, the need for epidemiological information has complemented virologic data collection. To adequately understand the burden and impact of influenza, morbidity-and mortality-related data are essential. Such data can be obtained from sentinel healthcare providers at outpatient clinics and emergency departments, influenza hospitalization surveillance networks, and health statistics offices for mortality surveillance [2] . The accumulation of annual surveillance data allows rapid assessment of influenza burden, and it may detect the beginning of a pandemic. These data will provide timely information for public health-related decision-making. For the adequate measurement and comparison of disease burden, standardization of surveillance data is critical. Influenza-like illness (ILI) and severe acute respiratory illness (SARI) are the most commonly used proxy respiratory syndrome indexes of influenza surveillance. ILI is generally intended for use in outpatient settings and the SARI, in hospital settings that provide inpatient treatment. SARI is used with the aim of capturing both cases of pneumonia and aggravation of chronic diseases such as asth-ma, chronic obstructive lung disease, or congestive heart failure. Influenza epidemiology can differ depending on various factors including region, ethnicity, proportions of age groups, and influenza vaccination rate.