Infectious Disease Epidemiology
Arizona Influenza Activity 2004-2005Summary of 2004-2005 influenza season
Influenza-like illness sentinel surveillance
The 2004-2005 influenza season was mild throughout the state and country. Arizona's first confirmed case of the season was identified in late October, with the peak of Arizona's flu season occurring in January and February, which is typical for the state. This season was the first in which flu was lab-reportable in Arizona, effective 10/02/2004, which helped ADHS to track and monitor the level of flu in Arizona. Positive flu labs were reported from 14 of Arizona's 15 counties this season. There were no reported influenza-associated deaths among Arizona children this season.
Nationally, the season started with predominantly influenza A circulating, but towards the end of the season the percentage of influenza B steadily increased. In addition, the A/Fujian-like H3N2 component of the influenza vaccine will be replaced by the new A/Californian strain in the 2005-2006 vaccine, based on national and international surveillance and antigenic characterization.
Beginning in the 2004-2005 season, laboratories were required to report positive influenza tests to ADHS. A total of 1,494 lab-confirmed cases of influenza were reported this season. Of these,730 were influenza A (292 confirmed by culture or PCR), 496 were influenza B (288 confirmed by culture or PCR) and the others 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 292 culture- or PCR-confirmed influenza A, 81 were H3N2, 105 were H3 with no N subtyping available, and the others were not subtyped. Ninety-three of the 288 influenza B isolates or PCRs were characterized as B/Shanghai/361/2002-like and 13 were characterized as B/Hong Kong.
Influenza-like illness (ILI) surveillance measures the proportion of patient visits to sentinel providers for ILI out of the total visits each week. Due to the mild influenza season, there was no distinct peak in the ILI numbers this season.
ILI data for the week ending April 9 includes reports from <50% of providers.