Results of tens of thousands of flu tests indicate that the pandemic H1N1 virus is spreading from school-aged children to the rest of the U.S. population, makers of the tests say.
Quest Diagnostics, which makes a commercially available test that can confirm swine flu infection, said the findings suggest many more adults will be infected with the new H1N1 influenza.
Based on tests performed since Quest Diagnostics began offering H1N1testing in May 2009, children between the ages of five to 14 have experienced higher overall rates of H1N1 positivity than any other age group, the company said in its report.
The Quest test is a PCR test -- it magnifies the genetic material of the virus so it can be detected and is similar to the tests used by state health departments to confirm H1N1.
On-the-spot flu tests given in doctor's offices only tell if a person has influenza A or not. They cannot tell which strain, and they often miss the new H1N1 strain completely.
The U.S. Centers for Disease Control and Prevention has given up trying to count how many people have the new H1N1, saying only that is it well over a million. Only select cases are tested.
The CDC reported that data from 27 U.S. states shows 53 percent of people sick enough to be hospitalized with H1N1 flu are under the age of 25, with only 7 percent of hospitalizations among people 65 and older -- a reversal of the trend seen with seasonal flu.
Dr. Jay Lieberman, medical director for Quest Diagnostics and a pediatrician at the University of California, Irvine, says data from Quest's testing, based on 76,500 specimens taken between May 11 and October 11, 2009, can supplement the CDC's findings, which cover fewer than 5,000 patients.
The sharp rise in cases in children came at the end of August and beginning of September, Lieberman told Reuters in a telephone interview.
What is interesting is that we are now seeing delayed by several weeks a rise in other age groups -- in the elderly, in people aged 50 to 64 and in children under 5 years of age, Lieberman said.
Influenza often spreads from school-aged children to siblings, parents and eventually grandparents./
What we have seen in the pandemic so far is that the elderly have been relatively spared. That may start to change in the weeks ahead, Lieberman said.
Many scientists think the elderly are less likely to be infected because they have some immunity to the H1N1 virus.
Lieberman said the findings show it is important to vaccinate children against influenza to slow the spread in the community.
Cases are evenly divided by gender, Quest said, and about half of all samples sent for testing -- by doctor's offices, state and county health departments -- turn out to be H1N1.
H1N1 has been mild to moderate so far. Lieberman said had it been a more pathogenic virus, causing severe disease in more people, officials likely would have closed schools to help slow its spread until more vaccines could have become available.