Weekly Report: Influenza Summary Update

2007-2008 Influenza Season Week 50, ending December 15, 2007

(All data are preliminary and may change as more reports are received.)

Synopsis

During week 50 (December 9-15, 2007), a low level of influenza activity was reported in the United States.

• Eighty-six (3.9%) specimens tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories were positive for influenza.
• The proportion of deaths attributed to pneumonia and influenza was below the epidemic threshold.
• The proportion of outpatient visits for influenza-like illness (ILI) and acute respiratory illness (ARI) was below national baseline levels. The Pacific region reported ILI equal to their region-specific baseline.
• One state reported regional influenza activity; five states reported local influenza activity; 36 states, the District of Columbia, and Puerto Rico reported sporadic influenza activity; and eight states reported no influenza activity.

National and Regional Summary of Select Surveillance Components

Region	Data for current week				Data cumulative for the season
	Sentinel Provider ILI*	DoD and VA ARI*	% pos. for flu†	# jurisdictions reporting regional or widespread activity‡	A (H1)	A (H3)	A Unsub-typed	B	Pediatric Deaths
Nation	Normal	Normal	3.9 %	1 of 51	179	43	537	72	1
New England	Normal	Normal	1.3 %	0 of 6	7	0	7	4	0
Mid-Atlantic	Normal	Normal	0.6 %	0 of 3	2	0	9	5	0
East North Central	Normal	Normal	3.7 %	0 of 5	4	5	5	4	0
West North Central	Normal	Normal	1.4 %	0 of 7	3	2	19	5	0
South Atlantic	Normal	Normal	3.8 %	0 of 9	3	8	149	22	0
East South Central	Normal	Normal	0.3 %	0 of 4	2	1	0	0	0
West South Central	Normal	Normal	6.2 %	0 of 4	8	23	260	8	1
Mountain	Normal	Normal	9.4 %	1 of 8	95	0	41	16	0
Pacific	Elevated	Normal	3.2 %	0 of 5	55	4	47	8	0

* Elevated means the % of visits for ILI or ARI is at or above the national or region-specific baseline
?National data is for current week; regional data is for the most recent 3 weeks.
?Includes all 50 states and the District of Columbia

Laboratory Surveillance

During week 50, WHO and NREVSS laboratories reported 2,207 specimens tested for influenza viruses, 86 (3.9%) of which were positive, including 22 influenza A (H1) viruses, five influenza A (H3) viruses, 49 influenza A viruses that were not subtyped, and 10 influenza B viruses. The District of Columbia and 37 states from all nine surveillance regions have reported laboratory-confirmed influenza this season.

Since September 30, 2007, WHO and NREVSS laboratories have tested a total of 33,163 specimens for influenza viruses and 831 (2.5%) were positive. Among the 831 influenza viruses, 759 (91.3%) were influenza A viruses and 72 (8.7%) were influenza B viruses. Two hundred twenty-two (29.2%) of the 759 influenza A viruses have been subtyped: 179 (80.6%) were influenza A (H1) viruses and 43 (19.4%) were influenza A (H3) viruses.

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Antigenic Characterization:

CDC has antigenically characterized 58 influenza viruses [32 influenza A (H1), 11 influenza A (H3), and 15 influenza B viruses] collected by U.S. laboratories since September 30, 2007.

Influenza A (H1) [32]

• All 32 viruses were characterized as A/Solomon Islands/3/2006, the influenza A (H1) component of the 2007-08 influenza vaccine for the Northern Hemisphere and the 2008 influenza A (H1) component for the Southern Hemisphere.

Influenza A (H3) [11]

• Four viruses were characterized as A/Wisconsin/67/2005-like, the influenza A (H3) component of the 2007-08 influenza vaccine for the Northern Hemisphere.
• Seven viruses were characterized as A/Brisbane/10/2007-like. 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.

Influenza B (B/Victoria/02/87 and B/Yamagata/16/88 lineages) [15]

Victoria lineage [0]
• The recommended influenza B component for the 2007-08 influenza vaccine is a B/Malaysia/2506/2004-like virus, belonging to the B/Victoria lineage.

Yamagata lineage [15]

• All 15 viruses were identified as belonging to the B/Yamagata lineage.

It is too early in the influenza season to determine which influenza viruses will predominate or how well the vaccine and circulating strains will match.

Pneumonia and Influenza (P&I) Mortality Surveillance

During week 50, 6.3% of all deaths reported through the 122-Cities Mortality Reporting System were reported as due to P&I. This percentage is below the epidemic threshold of 6.6% for week 50.

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Influenza-Associated Pediatric Mortality

No influenza-associated pediatric deaths were reported during week 50. One influenza-associated pediatric death has been reported during the 2007-08 season.

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Influenza-Associated Pediatric Hospitalizations

Laboratory-confirmed influenza-associated pediatric hospitalizations are monitored in two population-based surveillance networks: the New Vaccine Surveillance Network (NVSN) and the Emerging Infections Program (EIP).

No influenza-associated pediatric hospitalizations have been reported from the NVSN.

During September 30-December 8, 2007, the preliminary laboratory-confirmed influenza-associated hospitalization rate reported by the EIP for children 0?7 years old was 0.02 per 10,000. For children aged 0-4 years and 5-17 years, the rate was 0.03 per 10,000 and 0.005 per 10,000, respectively.

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Outpatient Illness Surveillance

Nationwide during week 50, 1.7% of patient visits reported through the U.S. Influenza Sentinel Provider Surveillance Network were due to influenza-like illness (ILI) and 2.5% of patient visits to Department of Veteran’s Affairs (VA) and Department of Defense (DoD) outpatient treatment facilities were for acute respiratory illness (ARI). These percentages are less than the national baselines of 2.2% and 3.2%, respectively. On a regional level, the percentage of visits for ILI ranged from 0.5% to 3.4% and the percentage of visits for ARI ranged from 1.2% to 3.0%. The Pacific region reported ILI equal to their region-specific baseline. All nine regions reported percentages of visits for ARI below their respective region-specific baselines. All five age groups reported percentages of visits for ARI below their respective age-specific baselines.

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Geographic Spread of Influenza as Assessed by State and Territorial Epidemiologists

During week 50 the following influenza activity was reported:

• Regional activity was reported by one state (Colorado).
• Local activity was reported by five states (Arizona, Hawaii, Massachusetts, Texas, and Virginia).
• Sporadic activity was reported by the District of Columbia, Puerto Rico, and 36 states (Alabama, Alaska, California, Connecticut, Delaware, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Michigan, Minnesota, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Dakota, Tennessee, Utah, Washington, Wisconsin, and Wyoming).
• No activity was reported by eight states (Arkansas, Idaho, Mississippi, Missouri, Ohio, South Carolina, Vermont, and West Virginia).

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A description of surveillance methods is available at: http://www.cy118119.com/flu/weekly/fluactivity.htm

• Page last updated December 21, 2007
• Content Source: Coordinating Center for Infectious Diseases (CCID)
• National Center for Immunization and Respiratory Diseases (NCIRD)