Purpose

Active surveillance for hospitalized laboratory-confirmed influenza cases among New Haven County, Connecticut residents is being conducted for the sixth consecutive influenza season. Laboratory-confirmed influenza is reportable to the Connecticut Department of Public Health (CTDPH). Using these reports and hospital records, 1889 laboratory-confirmed influenza infections and 431 influenza-related hospitalizations were identified during the 2007-08 influenza season. Thus far, during the 2008-09 influenza season (October 1, 2008-April 30, 2009), 1316 laboratory-confirmed influenza infections among New Haven County residents have been reported to CTDPH, of which, 182 (14%) were hospitalized. Of those hospitalized, 133 (73%) were adult cases and 49 (27%) were pediatric cases.

Goals & Objectives

• Determine the age-specific rates of laboratory confirmed influenza-associated hospitalization.
• Determine the rate of serious influenza-associated complications, such as secondary bacterial infections, and need for ICU admission/ mechanical ventilation.
• Describe clinical and epidemiologic characteristics of cases to identify factors associated with severe illness or influenza-associated complications.
• Evaluate the hospitalization rates obtained from various methods of identifying cases.
• Evaluate adherence to influenza vaccination recommendations.

Activities

Active surveillance for laboratory-confirmed influenza hospitalizations is conducted among New Haven County residents. A case is defined as a resident of the catchment area having a hospital admission with a laboratory-confirmed influenza assay within the typical influenza season. All positive laboratory tests for influenza A or influenza B are required by law to be reported to CTDPH. Those having a positive laboratory-confirmed influenza test reported to CTDPH are followed up to identify those requiring hospitalization. Demographic, primary care provider contact, diagnostic, and vaccination information are collected from the medical chart of cases and recorded on a standardized case report form. If insufficient information on vaccine history is recorded in the medical record, then vaccine information is collected through the use of a questionnaire.

This is a multi-site project conducted by eight other Emerging Infections Programs in the United States. Aggregate results will be shared with relevant Centers for Disease Control and Prevention programs, including the Advisory Committee on Immunization Practices. In Connecticut, surveillance among New Haven County residents < 18 years of age began during the 2003–2004 influenza season. Laboratory-confirmed influenza related hospitalization rates for the 2003-2004, 2004-05, 2005-06, 2006-07, and 2007-08 influenza seasons were 108, 47, 29, 21, and 26 per 100,000 population, respectively. Surveillance among New Haven County residents 18 years old and older began in the 2005-06 influenza season. During the 2005-06, 2006-07, and 2007-08 influenza seasons, the adult laboratory-confirmed hospitalization rates were 72, 42, and 66 per 100,000 population. Comprehensive and aggregate data analyses for this project are ongoing.

Related Links

Laboratory-confirmed Influenza Infections and Hospitalizations by MMWR Week, for New Haven County, Connecticut

CT DPH Flu Statistics


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Project Contact Person

Emerging Infections Program
Yale School of Public Health
1 Church Street, 7th Floor
New Haven, CT 06510
Phone: (203) 764-4360
Fax: (203) 764-4357