Sunday, January 31, 2010

H1N1 and Where Did It Go?

The CDC data on H1N1 shows a dramatic decline in incidence. They report:

During week 3 (January 17-23, 2010), influenza activity remained at approximately the same levels this week in the U.S.

  • 164 (4.6%) 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.
  • The proportion of deaths attributed to pneumonia and influenza (P&I) was above the epidemic threshold.
  • Five influenza-associated pediatric deaths were reported. Four 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 1.7% which is below the national baseline of 2.3%. Two of the 10 regions (Regions 4 and 9) reported ILI equal to their region-specific baseline.
  • No states reported widespread influenza activity, five states reported regional influenza activity, Puerto Rico and nine states reported local influenza activity, the District of Columbia, Guam, and 33 states reported sporadic influenza activity, and the U.S. Virgin Islands and three states reported no influenza activity.
It is interesting to consider and possibly determine why it has not had as high an impact as was originally anticipated. Was there a basic misunderstanding, did prevention work, are people more educated. It was clear that at MIT and at Brigham and Women's there was an aggressive approach to hand sanitizing and it clearly worked even in environments open to ready transmission.

This will be an interesting study some time when it is done.