The US Influenza Hospitalization Surveillance Network

Abstract

In 2003, surveillance for influenza in hospitalized persons was added to the Centers for Disease Control and Prevention Emerging Infections Program network. This surveillance enabled monitoring of the severity of influenza seasons and provided a platform for addressing priority questions associated with influenza. For enhanced surveillance capacity during the 2009 influenza pandemic, new sites were added to this platform. The combined surveillance platform is called the Influenza Hospitalization Surveillance Network (FluSurv-NET). FluSurv-NET has helped to determine the risk for influenza-associated illness in various segments of the US population, define the severity of influenza seasons and the 2009 pandemic, and guide recommendations for treatment and vaccination programs.

Keywords: EIP; Emerging Infections Program; FluSurv-NET; Influenza; US Influenza Hospitalization Surveillance Network; influenza hospitalizations; population-based surveillance; viruses.

Figure 1

Population-based influenza hospitalization surveillance case ascertainment and review process, Influenza Hospitalization Surveillance Network, United States. Core data transmitted weekly to the Centers for Disease Control and Prevention (CDC) are patient identification number, surveillance site, hospital admission date, patient’s date of birth, type of influenza test, and type of influenza virus. Case finding and chart reviews are done manually.

Figure 2

Screenshot of FluView web-based interaction application showing cumulative laboratory-confirmed influenza-associated hospitalizations per 100,000 population, United States. A) Age-specific rates by age groups; B) rates within specific age group, by influenza season. MMWR week defined at http://wwwn.cdc.gov/nndss/document/MMWR_Week_overview.pdf. Data from http://gis.cdc.gov/GRASP/Fluview/FluHospRates.html.

Figure 3

Screenshot of FluView web-based interaction application showing characteristics of hospitalized patients with laboratory-confirmed influenza in the United States by virus type; selected demographic characteristics, by influenza season; and prevalence of underlying medical conditions in children and adults. Data from http://gis.cdc.gov/grasp/fluview/FluHospChars.html.

Figure 4

Percentages of children and adults hospitalized with laboratory-confirmed influenza virus infection who received influenza antiviral treatment, during 2009–10 (total hospitalized patients = 8,866) and 2010–11 (total hospitalized patients = 6,040), United States. Numbers above bars denote numbers of patients who received influenza antiviral treatment. p<0.01 for all age groups and categories except for the age group >65 years (18). Data from FluSurv-NET.

Figure 5

Prevented fraction of influenza cases as a result of vaccination, by age group and influenza season, United States, 2005–06 through 2010–11 influenza seasons. Prevented fraction was defined as the proportion of averted outcomes out of potential outcomes in the absence of vaccination (15).