Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file

Weekly Report: Influenza Summary Update

Week ending January 29, 2005-Week 4

Error processing SSI file

The following information may be quoted:

Synopsis:

During week 4 (January 23-29, 2005)*, influenza activity continued to increase in the United States. Four hundred seventy-four (15.9%) specimens tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories were positive for influenza viruses. The proportion of patient visits to sentinel providers for influenza-like illness (ILI) is above the national baseline and the proportion of deaths attributed to pneumonia and influenza is below the epidemic threshold. There have been four influenza-associated pediatric deaths reported to CDC this season. Sixteen states reported widespread influenza activity, 19 states and New York City reported regional influenza activity, and 9 states and the District of Columbia reported local activity. Five states and Puerto Rico reported sporadic influenza activity.

Laboratory Surveillance*:

During week 4, WHO and NREVSS laboratories in the United States reported testing 2,986 specimens for influenza viruses, of which 474 (15.9%) were positive. Of these, 92 were influenza A (H3N2) viruses, 297 were influenza A viruses that were not subtyped, and 85 were influenza B viruses.

Since October 3, WHO and NREVSS laboratories in the United States have tested a total of 58,314 specimens for influenza viruses and 5,138 (8.8%) were positive. Among the 5,138 influenza viruses, 4,406 (85.8%) were influenza A viruses and 732 (14.2%) were influenza B viruses. One thousand two hundred eighty-five (29.2%) of the 4,406 influenza A viruses have been subtyped; 1,280 (99.6%) were influenza A (H3N2) and 5 (0.4%) were influenza A (H1N1) viruses. The largest numbers of specimens testing positive for influenza virus have been reported from the New England (1,061) and Mid-Atlantic (1,147) regions**. The percentage of total isolates that are influenza type A virus is the highest in these same regions: 97% in both the New England and Mid-Atlantic regions. Influenza A viruses represent a smaller proportion of positive results in the other seven regions, ranging from 89% in the West North Central region to 61% in the Mountain region.

INFLUENZA Virus Isolated


View Chart Data

Antigenic Characterization:

CDC has antigenically characterized 239 influenza viruses collected by U.S. laboratories since October 1, 2004: 2 influenza A (H1) viruses, 157 influenza A (H3N2) viruses, and 80 influenza B viruses. The hemagglutinin proteins of the influenza A (H1) viruses were similar antigenically to the hemagglutinin of the vaccine strain A/New Caledonia/20/99. One hundred twenty-five (95%) of 157 influenza A(H3N2) isolates were characterized as antigenically similar to A/Wyoming/3/2003, which is the A/Fujian/411/2002-like (H3N2) component of the 2004-05 influenza vaccine. Thirty-two (20%) influenza A(H3N2) isolates had reduced titers to A/Wyoming/3/2003 and are most closely related to a recent reference strain, A/California/7/2004 (H3N2). Sixty-four of the influenza B viruses isolated this season belong to the B/Yamagata lineage and were characterized as B/Shanghai/361/2002-like, which is the influenza B component recommended for the 2004-05 influenza vaccine, and 4 showed somewhat reduced titers to ferret antisera produced against B/Shanghai/361/2002. Sixteen influenza B viruses belong to the B/Victoria lineage.

Influenza B viruses currently circulating can be divided into two antigenically and genetically distinct lineages represented by B/Yamagata/16/88 and B/Victoria/2/87 viruses. B/Yamagata lineage viruses circulated widely between 1990 and 2001, during which time B/Victoria-like viruses were not identified outside of Asia. However, between March 2001 and October 2003, B/Victoria-like viruses predominated in many countries, including the United States, and the vaccine strains were changed accordingly. While both Victoria lineage and Yamagata lineage viruses have been reported worldwide during the past year, Yamagata lineage viruses have once again become predominant.

Pneumonia and Influenza (P&I) Mortality Surveillance*:

During week 4, 8.0% of all deaths reported by the vital statistics offices of 122 U.S. cities were attributed to pneumonia or influenza. This percentage is below the epidemic threshold of 8.1% for week 4.

Pneumonia And Influenza Mortality

View Full Screen

Influenza-Associated Pediatric Mortality*:

Four pediatric deaths have been reported to CDC: one from Maine in week 1, one from Massachusetts in week 2, one from California in week 3, and one from Ohio in week 4.

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). During October 3, 2004–January 22, 2005, the preliminary influenza-associated hospitalization rate for children 0–4 years old reported by the NVSN and EIP was 1.8 per 10,000 and 0.42 per 10,000, respectively. The EIP also monitors hospitalizations in children 5-17 years and the preliminary influenza-associated hospitalization rate for this age group was 0.07 per 10,000. The overall hospitalization rate reported by the EIP for children aged 0-17 years was 0.22 per 10,000. In years 2000–2003, the end-of-season hospitalization rate for the NVSN ranged from 3.7 to 12 per 10,000 children. The 2003-04 end of season hospitalization rate for the EIP was 7.8 per 10,000 children 0-4 years and 0.8 per 10,000 for children 5-17 years. The difference in rates between the NVSN and EIP could be due to different case finding methods and the different populations monitored. For a summary of the methods used in each system please refer to the surveillance methods in the Flu Activity section of the CDC Influenza website.

NVSN laboratory-confirmed influenza-associated hospitalizations for children 0-4 years old
View Full Screen

EIP Influenza Laboratory-Confirmed Cumulative Hospitalization Rates for Children 0-4 years and 5-17 years, 2004-05 and 2003-04
View Full Screen

Influenza-like Illness Surveillance*:

During week 4, 3.7%†† of patient visits to U.S. sentinel providers were due to ILI. This percentage is above the national baseline of 2.5%. The percentage of visits for ILI ranged from 1.8% in the New England region to 5.5% in the Mid-Atlantic region. Due to wide variability in regional level data, it is not appropriate to apply the national baseline to regional level data.

Bar Chart for Influenza-like Illness
View Chart Data | View Full Screen

Influenza Activity as Assessed by State and Territorial Epidemiologists*:

During week 4, 16 states (Colorado, Connecticut, Delaware, Iowa, Kansas, Kentucky, Maryland, Minnesota, New Jersey, New York, North Dakota, Pennsylvania, Texas, Vermont, Washington, and Wisconsin) reported widespread activity. Nineteen states (Arizona, Georgia, Idaho, Illinois, Louisiana, Maine, Massachusetts, Michigan, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, Oregon, South Dakota, Tennessee, Utah, and Virginia) and New York City reported regional influenza activity. Nine states (Alaska, Arkansas, Florida, Hawaii, Indiana, North Carolina, New Mexico, Ohio, and Wyoming) and the District of Columbia reported local activity. Five states (Alabama, California, Oklahoma, South Carolina, and West Virginia) and Puerto Rico reported sporadic influenza activity. Rhode Island did not report.

U. S. map for Weekly Influenza Activity
View Full Screen

--------------------------------------------------------------------------------

Footnotes

Report prepared: February 3, 2005

Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file