(Dec. 25, 2003) -- The Centers for Disease Control (CDC) says flu and pneumonia deaths in the U.S. reached the epidemic threshold and flu continued to increase nationally during the period Dec. 14 - 20, 2003.

"The proportion of deaths attributed to pneumonia and influenza was 7.8%, which equals the epidemic threshold for the week," CDC said.

The agency listed CA as among the 45 states in which flu activity was described as "widespread."

CDC said the proportion of patient visits to sentinel providers for influenza-like illness (ILI) overall was 7.7%, which is above the national baseline of 2.5%, and although ILI activity continues to increase overall, it declined in Texas and Colorado in recent weeks.

"Influenza activity in [Texas and Colorado] continues to be widespread, but in Texas, outpatient visits for ILI have declined from a peak of 14.4% during week 47 (the week ending November 22) to 7.4% during week 51. In Colorado, the percentage of patient visits for ILI peaked at 4.3% during week 48 (the week ending November 29) and has declined to 1.1% during week 51."

The agency added that during the past week, "there were insufficient data from WHO and NREVSS collaborating laboratories to report laboratory results."

CDC says that since Oct. 1 it has antigenically characterized 330 influenza viruses collected by U.S. laboratories and found two influenza A (H1) viruses, 326 influenza A (H3N2) viruses, and 2 influenza B viruses.

Of the 326 influenza A (H3N2) isolates characterized, 80 (25%) were similar antigenically to the vaccine strain A/Panama/2007/99 (H3N2)...but 246 (75%) were similar to the drift variant, A/Fujian/411/2002 (H3N2) [i.e., not in the vaccine.]

Both influenza B viruses characterized were similar antigenically to B/Sichuan/379/99, which is in the 2003-04 vaccine, CDC said.

For further information:

CDC flu update, week ending Dec. 20.

CDC flu page.

CDC Recommendations for Influenza Prevention