Weekly Report: Influenza Summary Update

2007-2008 Influenza Season Week 46, ending November 17, 2007

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

Synopsis

During week 46 (November 11-17, 2007), a low level of influenza activity was reported in the United States.

• Sixty-four (2.8%) 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 Mountain region reported ILI slightly above their region-specific baseline.
• Two states reported local activity; 20 states and the District of Columbia reported sporadic influenza activity; and 28 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	2.8 %	0 of 51	51	14	242	26	0
New England	Normal	Normal	0.7 %	0 of 6	3	0	2	2	0
Mid-Atlantic	Normal	Normal	0.2 %	0 of 3	0	0	3	0	0
East North Central	Normal	Normal	2.6 %	0 of 5	0	0	3	2	0
West North Central	Normal	Normal	0.1 %	0 of 7	2	1	4	1	0
South Atlantic	Normal	Normal	3.9 %	0 of 9	1	4	97	10	0
East South Central	Normal	Normal	0.7 %	0 of 4	1	1	0	0	0
West South Central	Normal	Normal	4.3 %	0 of 4	1	7	104	4	0
Mountain	Elevated	Normal	2.6 %	0 of 8	17	0	5	3	0
Pacific	Normal	Normal	3.2 %	0 of 5	26	1	24	4	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 46, WHO and NREVSS laboratories reported 2,265 specimens tested for influenza viruses, 64 (2.8%) of which were positive, including 10 influenza A (H1) viruses (Mountain, New England, and Pacific regions), one influenza A (H3) virus (West South Central region), and 53 influenza A viruses that were not subtyped (East North Central, Mountain, Pacific, South Atlantic, and West South Central regions). The District of Columbia and 25 states from all nine surveillance regions have reported laboratory-confirmed influenza this season with Florida, Hawaii, and Texas accounting for 257 (77.2%) of the 333 reported influenza viruses.

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Antigenic Characterization

CDC has antigenically characterized one influenza virus collected by U.S. laboratories since September 30, 2007. The influenza B virus was characterized as B/Florida/04/2006, belonging to the B/Yamagata lineage. Influenza B viruses currently circulating can be divided into two antigenically distinct lineages represented by the B/Yamagata/16/88 and B/Victoria/02/87 viruses. 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.

Pneumonia and Influenza (P&I) Mortality Surveillance

During week 46, 5.7% 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 6.2% for week 46.

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Influenza-Associated Pediatric Mortality

No influenza-associated pediatric deaths were reported during week 46. No deaths have been reported for 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 Emerging Infections Program (EIP) and the New Vaccine Surveillance Network (NVSN). No influenza-associated pediatric hospitalizations have been reported from the EIP. NVSN estimated rates of hospitalization for influenza will be reported every two weeks, beginning November 30, 2007.

Outpatient Illness Surveillance

Nationwide during week 46, 1.5% of patient visits reported through the U.S. Influenza Sentinel Provider Surveillance Network were due to influenza-like illness (ILI) and 2.2% 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 0.6% to 3.8% and the percentage of visits for ARI ranged from 1.1% to 2.5%. The Mountain region reported ILI above 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

Influenza activity was reported as local in two states (Florida and Hawaii) and as sporadic in 20 states (California, Colorado, Connecticut, Illinois, Indiana, Iowa, Kentucky, Louisiana, Massachusetts, Minnesota, Nevada, New Jersey, New York, Oklahoma, Oregon, Pennsylvania, South Dakota, Tennessee, Texas, and Utah) and the District of Columbia. Twenty-eight states reported no influenza activity.

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

• Page last updated November 26, 2007
• Content Source: Coordinating Center for Infectious Diseases (CCID)
• National Center for Immunization and Respiratory Diseases (NCIRD)