The number of specimens that tested positive for 2009 H1N1 influenza has declined in all age groups since late October. Children ages five to 14 continue to experience the highest percentage of H1N1 positive test results compared to negative results, with a positivity rate of close to 40 percent. "Our findings suggest that children continue to be most vulnerable to the H1N1 virus," said Dr. Lieberman.Nearly every region experienced declines of 60 percent or more in positive test results during the two weeks ending December 9 compared to the two weeks ending November 25. The most striking decline in positive test results occurred in the region comprised by Pennsylvania, Maryland, Delaware, Virginia and West Virginia, and the District of Columbia (87 percent decline).The 2009 H1N1 influenza virus remains the predominant cause of influenza in the U.S., as more than 98 percent of positive influenza A specimens are positive for 2009 H1N1 influenza. "Our data provide no evidence that seasonal influenza viruses have begun to circulate," added Dr. Lieberman.

The Quest Diagnostics investigators believe the decline in testing demand is due to several factors, primarily lower rates of infection due to millions of Americans having already been infected with this influenza virus and the impact of H1N1 vaccines, both of which have reduced the number of people susceptible to infection, and changes in physician test-ordering practices.