Infectious Disease Epidemiology
Arizona Influenza Activity 2005-2006Summary of 2005-2006 influenza season
Influenza-like illness sentinel surveillance
activity peaked early in the 2005-2006 season, with the highest number of cases
seen during the last week of December. All
15 counties reported positive flu labs and there were two influenza-associated
deaths among Arizona children this season.
Labs have been required to report positive influenza tests to ADHS since 2004. A total of 5,197 lab-confirmed cases of influenza were reported during the 2005-2006 season. Of these, 4,018 cases were influenza A (769 confirmed by culture or PCR), 340 cases were influenza B (91 confirmed by culture or PCR), and 839 cases were non-specific rapid tests.
Viral isolation, or culture, is currently the "gold standard" for diagnosis of influenza virus infections. Subsequent laboratory testing of influenza culture-positive specimens can be used to identify the influenza A subtype. This subtyping analysis is performed on a subset of lab-confirmed cases. Polymerase chain reaction (PCR) can also be used to identify influenza B and the hemagglutinin (H) component of influenza A. Of the 769 culture- or PCR-confirmed influenza A, 68 were H3N2, 307 were H3 with no N subtyping available, and the others were not subtyped.
More cases were reported from the 1-19 year age group (32%) than any other, but the incidence rate of reported cases was highest among infants less than 1 year of age.
Influenza-like illness (ILI) surveillance measures the proportion of patient visits to sentinel providers for ILI out of the total visits each week. A distinct peak in ILI was observed in the latter half of December, mirroring the peak in laboratory-confirmed influenza.
ILI data for May are based on reports from <50% of providers.
National information about the 2005-2006 influenza season can be found at the CDC influenza website.