Flu Season Activity in King County

Learn about Public Health – Seattle & King County’s Influenza Surveillance Program.

Weekly snapshot
Influenza continues to circulate at low levels in the community. Several long-term care facilities reported influenza outbreaks since the beginning of March, with the most recent report occurring in early May. King County pneumonia and influenza mortality exceeded the epidemic threshold several times this season, consistent with national data, which show that P&I mortality has exceeded the epidemic threshold for 18 consecutive weeks.

Sentinel Provider Surveillance through the Public Health Laboratory:

During week 19 (ending 5/10/2008), sentinel providers submitted 8 specimens for testing, 4 of which were positive for influenza, and one of which was positive for parainfluenza.

Since September 30, 2007, the PHSKC lab has received 614 specimens for respiratory virus culture, yielding

87 influenza A (H1)
44 influenza A (H3)
41 influenza A (not typed)
64 influenza B/Yamagata lineage
2 influenza B/Victoria lineage
9 influenza B (not typed)
8 adenovirus
1 parainfluenza type 1
1 parainfluenza type 3
6 respiratory syncytial virus (RSV)

Specimens that test positive for influenza are forwarded to the Centers for Disease Control and Prevention (CDC) laboratories for further antigenic characterization. CDC has characterized: 9 King County influenza A (H1) isolates from November and December 2007 as A/Solomon Islands/03/2006-like (H1N1) (contained in 2007-08 vaccine), 1 influenza A (H1) isolate from December 2007 as A/Solomon Islands/03/2006-like (H1N1) low (reduced coverage by 2007-08 vaccine), and 2 influenza A (H3) isolates from December 2007 as A/Brisbane/10/2007-like (H3N2). A/Brisbane/10/2007 is a recent antigenic variant which evolved from A/Wisconsin/67/2005-like. A/Brisbane/10/2007-like virus is the recommended influenza A (H3) component for the 2008 Southern Hemisphere vaccine. Additionally, 1 influenza A (H3) from January 2008 was characterized as A/Wisconsin/67/2005-like (H3N2) (contained in 2007-08 vaccine), and 1 influenza B/Yamagata lineage from January 2008 was characterized as B/Florida/04/2006-like (recommended component for 2008-09 vaccine).

To compare this year’s influenza season with previous seasons, click to enlarge the images below.

During week 19, 13% of rapid influenza antigen tests at hospital microbiology labs were positive for influenza (click on table to view data by week). The peak in proportion of tests positive for influenza occurred during week 4 at 30% and has declined since then. Overall, rapid antigen test results this season-to-date are comparable to the mean level for the previous four seasons. For information on respiratory virus detections visit University of Washington’s Clinical Virology Lab.

Syndromic Surveillance:
ED visits for febrile illness and ILI peaked during weeks 5 through 9 and have declined since then. Compared to the previous 3 seasons, the proportion of ED visits attributed to ILI was slightly higher among children under the age of five, and is comparable to previous years for other age groups.

P & I (Pneumonia and Influenza) Deaths:
King County P&I deaths have exceeded the national epidemic threshold nine times during the 2007-08 season, most recently during week sixteen. Nationally, P&I deaths have exceeded the national epidemic threshold for eighteen consecutive weeks. No pediatric influenza deaths have been reported in King County during the 2007-08 season.

Long-term Care Facilities:
Fourteen LTCF have reported outbreaks of ILI this season-to-date, eight of which were reported during the month of March. Six facilities reported positive influenza A test results and five reported influenza B. Other facilities had negative influenza testing.

School Absenteeism:
For the 2007-08 school year, King County schools were asked to report weekly absenteeism online, whether or not absenteeism exceeded 10% in a given week. Absenteeism greater than 10% peaked during weeks 5 and 6 and has continued at low levels since then. Overall, the absenteeism reports to date exceed those observed in previous years, but may in part be due to a change in the reporting mechanism.

During week 19 (May 4 – 10, 2008), influenza activity continued to decrease in the United States. The proportion of deaths attributed to pneumonia and influenza has been above the epidemic threshold for 18 consecutive weeks. The proportion of outpatient visits for influenza-like illness (ILI) and the proportion of outpatient visits for acute respiratory illness (ARI) were below national baseline levels. ILI was at the region-specific baseline in one region (New England), while the proportion of outpatient visits reported for ARI was below all region and age-specific baselines. One state reported regional influenza activity; two states reported local influenza activity; 28 states and Puerto Rico reported sporadic influenza activity; and 19 states and the District of Columbia reported no influenza activity.

Since September 30, 2007, 18 counties have reported 901 positive influenza isolates. Forty-Four (4.8%) were influenza A (H3N2), 100 (11%) were A, (H1N1), 436 (48.3%) were A, (Not Typed), and 321 (35.9%) were influenza B. A majority of the influenza B isolates looked at further were influenza B, Yamagata (not in this year’s vaccine). Isolation submission peaked the week ending February 2, 2008 with 12% of all isolates received. Submissions received have been falling steadily for the past four weeks with last weeks isolates received accounting for only 3.8% of all isolates received. Eighteen nursing home/adult living facilities have reported influenza outbreaks this season. Ten have been influenza B outbreaks and 8 have been influenza A. Influenza activity in Washington State is being reported as Local to the Centers for Disease Control (CDC).

Influenza activity continues to decrease across BC. The number of isolates decreased and the percent positive for influenza remains consistent at approximately 30%. For the first time since week 8, more specimens were reported as influenza A than B. Reports of outbreaks remained low.