2009-2010 Influenza Season Week 1 ending January 9, 2010

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

Synopsis:

During week 1 (January 3-9, 2010), influenza activity continued to decrease in the U.S.

• 139 (3.6%) specimens tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories and reported to CDC/Influenza Division were positive for influenza.
• All subtyped influenza A viruses reported to CDC were 2009 influenza A (H1N1) viruses.
• One human infection with a novel influenza A virus was reported.
• The proportion of deaths attributed to pneumonia and influenza (P&I) was below the epidemic threshold.
• Seven influenza-associated pediatric deaths were reported. Six deaths were associated with 2009 influenza A (H1N1) virus infection and one was associated with an influenza A virus for which the subtype was undetermined.
• The proportion of outpatient visits for influenza-like illness (ILI) was 1.9% which is below the national baseline of 2.3%. One of the 10 regions (region 9) reported ILI above their region-specific baseline.
• No states reported widespread influenza activity, nine states reported regional influenza activity, the District of Columbia, Puerto Rico, and 15 states reported local influenza activity, Guam and 24 states reported sporadic influenza activity, and the U.S. Virgin Islands and two states reported no influenza activity.

*Influenza season officially begins each year at week 40. This season data from week 35 will be included to show the trend of influenza activity before the official start of the 2009-10 influenza season.
**HHS regions (Region 1 CT, ME, MA, NH, RI, VT; Region 2: NJ, NY, Puerto Rico, US Virgin Islands; Region 3: DE, DC, MD, PA, VA, WV; Region 4: AL, FL, GA, KY, MS, NC, SC, TN; Region 5: IL, IN, MI, MN, OH, WI; Region 6: AR, LA, NM, OK, TX; Region 7: IA, KS, MO, NE; Region 8: CO, MT, ND, SD, UT, WY; Region 9: AZ, CA, Guam, HI, NV; and Region 10: AK, ID, OR, WA).
† Elevated means the % of visits for ILI is at or above the national or region-specific baseline
‡ National data are for current week; regional data are for the most recent three weeks
§ Includes all 50 states, the District of Columbia, Guam, Puerto Rico, and U.S. Virgin Islands
￥ Subtyping results for the majority of specimens in this category were inconclusive because of low virus titers.

U.S. Virologic Surveillance:

WHO and NREVSS collaborating laboratories located in all 50 states and Washington D.C., report to CDC the number of respiratory specimens tested for influenza and the number positive by influenza type and subtype. The results of tests performed during the current week are summarized in the table below.

	Week 1
No. of specimens tested	3,886
No. of positive specimens (%)	139 (3.6%)
Positive specimens by type/subtype
Influenza A	137 (98.6%)
A (2009 H1N1)	78 (56.9%)
A (subtyping not performed)	58 (42.3%)
A (unable to subtype)*	1 (0.7%)
A (H3)	0 (0.0%)
A (H1)	0 (0.0%)
Influenza B	2 (1.4%)

*Subtyping results for the specimen in this category was inconclusive because of low levels of viral RNA.

During week 1, influenza B viruses co-circulated at low levels with 2009 influenza A (H1N1) viruses. All subtyped influenza A viruses reported to CDC this week were 2009 influenza A (H1N1) viruses.

View WHO-NREVSS Regional Bar Charts | View Chart Data | View Full Screen | View PowerPoint Presentation

Novel Influenza A Virus:

One case of human infection with a novel influenza A virus was reported by the Iowa Department of Public Health. The case patient had onset of symptoms in September 2009, but did not require hospitalization and has fully recovered. The virus was identified as swine influenza A (H3N2) and investigated in November 2009. No clear exposure to swine was identified, but no evidence of sustained human-to-human transmission with this virus was found. Early identification and investigation of novel influenza A cases is critical to evaluate the extent of the outbreak and possible human-to-human transmission. Surveillance for human infections with novel influenza A viruses is conducted year-round.

Pneumonia and Influenza Hospitalization and Death Tracking:

The Aggregate Hospitalization and Death Reporting Activity (AHDRA) system was implemented on August 30, 2009, and replaces the weekly report of laboratory confirmed 2009 H1N1-related hospitalizations and deaths that began in April 2009. Jurisdictions can now report to CDC counts of hospitalizations and deaths resulting from all types or subtypes of influenza, not just those from 2009 H1N1 influenza virus. To allow jurisdictions to implement the new case definition, counts were reset to zero on August 30, 2009. From August 30, 2009 – January 9, 2010, 38,454 laboratory-confirmed influenza-associated hospitalizations and 1,779 laboratory-confirmed influenza-associated deaths were reported to CDC. CDC will continue to use its traditional surveillance systems to track the progress of the 2009-10 influenza season.

View Full Screen | View Chart Data | View PowerPoint Presentation

Antigenic Characterization:

CDC has antigenically characterized one seasonal influenza A (H1N1), seven influenza A (H3N2), six influenza B, and 944 2009 influenza A (H1N1) viruses collected since September 1, 2009.

One seasonal influenza A (H1N1) virus was tested and is related to the influenza A (H1N1) component of the 2009-10 Northern Hemisphere influenza vaccine (A/Brisbane/59/2007).

The seven influenza A (H3N2) viruses tested showed reduced titers with antisera produced against A/Brisbane/10/2007, the 2009-2010 Northern Hemisphere influenza A (H3N2) vaccine component, and were antigenically related to A/Perth/16/2009, the WHO recommended influenza A (H3N2) component of the 2010 Southern Hemisphere vaccine formulation.

Influenza B viruses currently circulating globally can be divided into two distinct lineages represented by the B/Yamagata/16/88 and B/Victoria/02/87 viruses. The influenza B component of the 2009-10 vaccine belongs to the B/Victoria lineage. The six influenza B viruses tested belong to the B/Victoria lineage and are related to the influenza vaccine component for the 2009-10 Northern Hemisphere influenza vaccine (B/Brisbane/60/2008).

Nine hundred forty-two (99.8%) of 944 2009 influenza A (H1N1) viruses tested are related to the A/California/07/2009 (H1N1) reference virus selected by WHO as the 2009 H1N1 vaccine virus. Two viruses (0.3%) tested showed reduced titers with antiserum produced against A/California/07/2009.

Annual influenza vaccination is expected to provide the best protection against those virus strains that are related to the vaccine strains, but limited to no protection may be expected when the vaccine and circulating virus strains are so different as to be from different lineages. Antigenic characterization of 2009 influenza A (H1N1) viruses indicates that these viruses are only distantly related antigenically and genetically to seasonal influenza A (H1N1) viruses, suggesting that little to no protection would be expected from vaccination with seasonal influenza vaccine. It is too early in the influenza season to determine if seasonal influenza viruses will circulate widely or how well the seasonal vaccine and circulating strains will match.

Antiviral Resistance:

Since September 1, 2009, one seasonal influenza A (H1N1), eight influenza A (H3N2), one influenza B, and 830 2009 influenza A (H1N1) virus isolates have been tested for resistance to the neuraminidase inhibitors (oseltamivir and zanamivir), and 2,096 2009 influenza A (H1N1) original clinical samples were tested for a single known mutation in the virus that confers oseltamivir resistance. In addition, one seasonal influenza A (H1N1), 11 influenza A (H3N2), and 837 2009 influenza A (H1N1) virus isolates have been tested for resistance to the adamantanes (amantadine and rimantadine). The results of antiviral resistance testing performed on these viruses are summarized in the table below. Additional laboratories perform antiviral testing and report their results to CDC and positive results from that testing are included in the footnote.

Antiviral Resistance Testing Results on Samples Collected Since September 1, 2009.

	Samples tested (n)	Resistant Viruses, Number (%)	Samples tested (n)	Resistant Viruses, Number (%)	Samples tested (n)	Resistant Viruses, Number (%)
		Oseltamivir		Zanamivir		Adamantanes
Seasonal Influenza A (H1N1)	1	1 (100.0)	0	0 (0)	1	0 (0)
Influenza A (H3N2)	8	0 (0)	0	0 (0)	11	9 (81.8)
Influenza B	1	0 (0)	0	0 (0)	N/A*	N/A*
2009 Influenza A (H1N1)	2,926	39?? (1.3)	830	0 (0)	837	834 (99.6)

*The adamantanes (amantadine and rimantadine) are not effective against influenza B viruses.
†Two screening tools were used to determine oseltamivir resistance: sequence analysis of viral genes or a neuraminidase inhibition assay.
‡Additional laboratories perform antiviral resistance testing and report their results to CDC. Three additional oseltamivir resistant 2009 influenza A (H1N1) virus has been identified by these laboratories since September 1, 2009, bringing the total number to 42.

All of the subtyped influenza A viruses reported during week 1 were 2009 influenza A (H1N1) viruses, and nearly all of 2009 H1N1 viruses tested since April 2009 have been resistant to the adamantanes (amantadine and rimantadine).

Antiviral treatment with oseltamivir or zanamivir is recommended for all patients with confirmed or suspected influenza virus infection who are hospitalized or who are at higher risk for influenza complications. Additional information on antiviral recommendations for treatment and chemoprophylaxis of influenza virus infection is available at http://www.cy118119.com/h1n1flu/recommendations.htm.

2009 influenza A (H1N1) viruses were tested for oseltamivir resistance by a neuraminidase inhibition assay and/or detection of genetic sequence mutation, depending on the type of specimen tested. Original clinical samples were examined for a single known mutation in the virus that confers oseltamivir resistance in currently circulating seasonal influenza A (H1N1) viruses, while influenza virus isolates were tested using a neuraminidase inhibition assay that determines the presence or absence of neuraminidase inhibitor resistance, followed by neuraminidase gene sequence analysis of resistant viruses.

The majority of 2009 influenza A (H1N1) viruses are susceptible to the neuraminidase inhibitor antiviral medication oseltamivir; however, rare sporadic cases of oseltamivir resistant 2009 influenza A (H1N1) viruses have been detected worldwide. A total of 52 cases of oseltamivir resistant 2009 influenza A (H1N1) viruses have been identified in the United States since April 2009. While the total number of cases has not increased over the previous week, one previously reported case was reclassified and one new case was identified. Forty-two of these specimens were collected after September 1, 2009. The proportion of oseltamivir-resistant 2009 H1N1 viruses does not represent the prevalence of oseltamivir-resistant 2009 H1N1 in the U.S. Most cases were tested because drug resistance was suspected. All tested viruses retain their sensitivity to the neuraminidase inhibitor zanamivir. Of the 52 total cases identified since April 2009, 40 patients had documented exposure to oseltamivir through either treatment or chemoprophylaxis, nine patients are under investigation to determine exposure to oseltamivir, and three patients had no documented oseltamivir exposure. Occasional development of oseltamivir resistance during treatment or prophylaxis is not unexpected. Enhanced surveillance, an increased availability of testing performed at CDC, and an increasing number of public health and other clinical laboratories performing antiviral resistance testing increase the number of cases of oseltamivir resistant 2009 influenza A (H1N1) viruses detected. All cases are investigated to assess the spread of resistant strains in the community.

To prevent the spread of antiviral resistant virus strains, CDC reminds clinicians and the public of the need to continue hand and cough hygiene measures for the duration of any symptoms of influenza, even while taking antiviral medications (http://www.cy118119.com/mmwr/preview/mmwrhtml/mm5832a3.htm).

Pneumonia and Influenza (P&I) Mortality Surveillance

During week 1, 7.3% of all deaths reported through the 122-Cities Mortality Reporting System were due to P&I. This percentage was below the epidemic threshold of 7.6% for week 1.

View Full Screen | View PowerPoint Presentation

Influenza-Associated Pediatric Mortality

Seven influenza-associated pediatric deaths were reported to CDC during week 1 (Illinois, Michigan, New York [2], Oregon, and Texas [2]). Six deaths were associated with 2009 influenza A (H1N1) virus infection and one was associated with an influenza A virus for which the subtype was undetermined.. The deaths reported during week 1 occurred between October 11 and December 19, 2009.

Since August 30, 2009, CDC has received 236 reports of influenza-associated pediatric deaths that occurred during the current influenza season (43 deaths in children less than 2 years old, 26 deaths in children 2-4 years old, 87 deaths in children 5-11 years old, and 80 deaths in children 12-17 years old). One hundred ninety-five (83%) of the 236 deaths were due to 2009 influenza A (H1N1) virus infections, 40 were associated with an influenza A virus for which the subtype is undetermined, and one was associated with an influenza B virus infection. A total of 255 deaths in children associated with 2009 influenza A (H1N1) virus infection have been reported to CDC.

Among the 236 deaths in children, 121 children had specimens collected for bacterial culture from normally sterile sites and 39 (32.2%) of the 121 were positive; Streptococcus pneumoniae was identified in 10 (25.6%) of the 39 children and Staphylococcus aureus was identified in 11 (28.2%) of the 39 children. Two S. aureus isolates were sensitive to methicillin, eight were methicillin resistant, and one did not have sensitivity testing performed. Twenty-six (66.7%) of the 39 children with bacterial coinfections were five years of age or older, and 14 (35.9%) of the 39 children were 12 years of age or older.

Laboratory-Confirmed Influenza-Associated Pediatric Deaths by Date and Type/Subtype of Influenza.

Date	2009 H1N1 Influenza	Influenza A-Subtype Unknown	Seasonal Influenza	Total
Number of Deaths REPORTED for Current Week – Week 1 (Week ending January 9, 2010)	6	1	0	7
Number of Deaths OCCURRED since August 30, 2009	195	40	1	236
Number of Deaths OCCURRED since April 26, 2009	255	43	2	300

View Full Screen | View PowerPoint Presentation

Influenza-Associated Hospitalizations

Laboratory-confirmed influenza-associated hospitalizations are monitored using a population-based surveillance network that includes the 10 Emerging Infections Program (EIP) sites (CA, CO, CT, GA, MD, MN, NM, NY, OR and TN) and 6 new sites (IA, ID, MI, ND, OK and SD).

During September 1, 2009 – January 9, 2010, the following preliminary laboratory-confirmed overall influenza associated hospitalization rates were reported by EIP and the new sites (rates include influenza A, influenza B, and 2009 influenza A (H1N1)):

Rates [EIP (new sites)] for children aged 0-4 years and 5-17 years were 5.9 (9.7) and 2.5 (3.6) per 10,000, respectively. Rates [EIP (new sites)] for adults aged 18-49 years, 50-64 years, and ≥ 65 years were 2.2 (1.7), 2.9 (1.8) and 2.4 (1.7) per 10,000, respectively.

*The 2008-09 EIP rate ended as of April 14, 2009 due to the onset of the 2009 H1N1 season.

View Full Screen | View PowerPoint Presentation

Outpatient Illness Surveillance:

Nationwide during week 01, 1.9% of patient visits reported through the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) were due to influenza-like illness (ILI). This percentage is above the national baseline of 2.3%.

The increase in the percentage of outpatient visits for ILI during weeks 51 and 52 is likely influenced by a reduction in routine health care visits during the holiday season, as has occurred during previous seasons.

View ILINet Regional Charts | View Chart Data | View Full Screen | View PowerPoint Presentation

On a regional level, the percentage of outpatient visits for ILI ranged from 0.6% to 3.8% during week 1. One of the 10 regions (Region 9) reported a proportion of outpatient visits for ILI above its region-specific baseline levels. Regions 1, 2, 3, 4, 5, 6, 7, 8, and 10 reported ILI below their region-specific baselines. (Note: Use of the national baseline for regional ILI data or regional baselines for state-level data is not appropriate.)

Geographic Spread of Influenza as Assessed by State and Territorial Epidemiologists:

The influenza activity reported by state and territorial epidemiologists indicates geographic spread of both seasonal influenza and 2009 influenza A (H1N1) viruses and does not measure the severity of influenza activity.

• During week 1, the following influenza activity was reported:
  • No states reported widespread influenza activity.
  • Regional influenza activity was reported by nine states (Alabama, Georgia, Hawaii, Maine, Nevada, New Jersey, New Mexico, New York, and Virginia).
  • Local influenza activity was reported by the District of Columbia, Puerto Rico, and 15 states (Alaska, Arizona, California, Connecticut, Louisiana, Massachusetts, Mississippi, New Hampshire, North Carolina, Oklahoma, Oregon, South Carolina, Tennessee, Texas, and Washington).
  • Sporadic influenza activity was reported by Guam and 24 states (Arkansas, Colorado, Delaware, Florida, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Maryland, Michigan, Minnesota, Missouri, Montana, North Dakota, Ohio, Pennsylvania, Rhode Island, South Dakota, Utah, Vermont, West Virginia, and Wisconsin).
  • The U.S. Virgin Islands and two states (Nebraska and Wyoming) reported no influenza activity.