INFLUENZA

There has been considerable concern of an impending influenza pandemic. I have reproduced below some reports from CDC and WHO of the current influenza status in USA and worldwide. For more information on Influenza please go to http://www.vadscorner.com/influenza.html .

From CDC :

Synopsis: During week 2 (January 9 through January 15), 21% of specimens tested by WHO and NREVSS laboratories for influenza were positive. State and territorial epidemiologists from 30 states reported widespread influenza activity, and 12 from other states reported regional influenza activity. The proportion of patient visits to sentinel physicians for influenza-like illness was 4% overall in the United States, exceeding baseline levels of 0% to 3%, and were above the baseline in 6 of 9 surveillance regions. The proportion of deaths attributed to pneumonia and influenza was 10.5%. This percentage is above the epidemic threshold for week 2 and is unusually high.

During the current season, the overall national percentage of respiratory specimens positive for influenza appears to have peaked at 33% during week 51. During the past 3 years, the peak percentages of respiratory specimens testing positive for influenza viruses have ranged from 28% to 34%. For this season, the percentage of patient visits for influenza-like illness appears to have peaked at 6% during week 52. During the past 3 years, the peak percentages for such visits have ranged between 5% and 7%. So far, the proportion of deaths attributed to pneumonia and influenza (P&I) has not clearly peaked. During the previous 3 years, P&I mortality levels have peaked between 8.8% and 9.1%. The current season's P&I figures must be interpreted with caution because important changes have taken place in this year's case definition that may be contributing to higher estimates of P&I mortality than in previous years.

U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) Collaborating Laboratory Reports*: During week 2, WHO and NREVSS laboratories tested 2,089 specimens for influenza viruses and 449 (21%) were positive. One hundred twenty-two were influenza A(H3N2) viruses, 318 were unsubtyped influenza A viruses and 9 were influenza type B. In 3 regions (New England, West North Central, and West South Central), more than 30% of specimens tested over the past 3 weeks (weeks 52 through 2) were positive for influenza (range 31% to 37%). In the remaining 5 regions, the percentage of specimens testing positive for influenza ranged from 15% to 29% during the past 3 weeks.

Since October 3, WHO and NREVSS laboratories have tested a total of 41,034 respiratory specimens for influenza viruses, and 7,361 (18%) were positive. Of the positive results, 7,338 (99.7%) were influenza type A and 23 (0.3%) were influenza type B. Of the 7,338 influenza A viruses, 1,665 (23%) have been subtyped and 1,659 (99.6%) were A(H3N2) and 6 (0.4%) were A(H1N1).

Antigenic Characterization of Viral Isolates: CDC has antigenically characterized 179 influenza viruses received from U.S. laboratories since October 1. Of the 172 influenza A(H3N2) viruses tested, 158 (92%) were similar to the vaccine strain A/Sydney/05/97 and 14 (8%) showed somewhat reduced titers to ferret antisera produced against A/Sydney/05/97. All 4 of the influenza B viruses antigenically characterized were similar to B/Beijing/184/93, which is represented in the current vaccine by B/Yamanashi/166/98. Of the 3 influenza A(H1N1) viruses antigenically characterized, 2 were similar to A/Beijing/262/95, the H1N1 component of the current vaccine, while 1 was more closely related to the antigenic variant A/New Caledonia/20/99.

Pneumonia and Influenza Mortality*: During week 2, the proportion of deaths due to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 10.5%. This percentage is above the epidemic threshold of 7.4% for week 2 and is unusually high. The percentage of pneumonia and influenza deaths has exceeded threshold values for this time of year for 16 of the past 17 weeks. Whether this increase in the percentage of pneumonia and influenza deaths is due to influenza activity, respiratory illness due to some other pathogen, or reporting changes under way in the 122 Cities Mortality Reporting System is unknown. However, because these changes include a revision of the reporting case definition, the current increase in pneumonia and influenza mortality should be interpreted with caution.

From WHO:

Current situation can be viewed at FluNet . The recommended vaccine for the current epidemic by WHO can be viewed at

  • for 2005 "southern hemisphere"
  • for 2005-2006 "northern hemisphere"
  • This has also been highlighted by Prof.Lam Sai Kit's article in this issue.(Influenza in the World)

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