Results from flu tests show the pandemic of swine flu is definitely on the downswing in the United States, researchers at Quest Diagnostics said on Friday.

The report supports what U.S. health officials have said - the H1N1 is ebbing across much of the United States, having reached a second peak in October.

“Children ages 5 to 14 continue to experience the highest percentage of H1N1 positive test results compared to negative results, with a positivity rate close to 40 percent. By comparison, nearly 80 percent of children in this age group tested positive for the virus in late October,” Quest said in a statement.

The company analyzed 170,000 flu tests taken between May and December to map out two peaks in the U.S. epidemic - one in April and one at the end of October.

“Between this peak week and December 9, testing rates fell by 75 percent. In the most recent week reported, December 9, testing rates were equivalent to volumes experienced in late August, when the second wave began,” the company said.

Flu often passes in waves, with several peaks in a single season. H1N1 emerged in March, just as flu is generally winding down in the northern hemisphere, and circulated globally all summer long.

It has so far completely overshadowed seasonal influenza, which generally begins circulating in the United States in October and peaks in February.

Quest’s Dr. Jay Lieberman said there could be several reasons for the decline in positive H1N1 tests.

“These include previous infection of tens of millions of Americans with this influenza virus as well as H1N1 vaccinations, which have reduced the number of susceptible patients, and changes in physician test ordering practices,” the statement reads.

STRIKING DECLINE

“The most striking decline in positive test results occurred in the region comprised by Pennsylvania, Maryland, Delaware, the District of Columbia, and Virginia and West Virginia where testing rates fell 87 percent during the two weeks ending December 9 compared to the prior two-week period.”

The results show that people are getting sick from a range of infections besides flu. Doctors usually only order flu tests for patients who are seriously ill or at risk of becoming seriously ill and thus would benefit from antiviral drugs such as Roche AG’s Tamiflu or GlaxoSmithkline’s Relenza.

But just 44 percent of suspected flu cases tested positive for H1N1 in November, and just 21 percent of specimens sent in December were positive for H1N1, Quest said.

U.S. health officials said this week that 100 million doses of H1N1 vaccine were now available or had been delivered and urged everyone to get vaccinated. H1N1 could still peak again and could also mutate into a more dangerous form.

The U.S. Centers for Disease Control and Prevention estimates that 47 million Americans have been infected with H1N1, nearly 10,000 have been killed by it and more than 200,000 hospitalized.

While the severity appears somewhat milder than seasonal flu, which kills an estimated 36,000 people a year, most patients who die or have severe disease from swine flu are children or non-elderly adults.

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* Flu peaked in late October, tests show

* Children still hardest-hit

* Nearly 80 percent of people tested had something else

By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters)