The number of cases of childhood influenza in the United States has been grossly underestimated, researchers have found. More often than not, doctors fail to correctly diagnose flu in their young patients.

Results of the research, led by Dr. Katherine Poehling, Vanderbilt Children's Hospital in Nashville, Tenn., are detailed in the New England Journal of Medicine.

More Than 70% of Cases Missed

The findings indicate that influenza is much more common among children in the United States than had been thought, and underscore the importance of providing vaccinations to this population.

During the study period of 2000 to 2004, doctors recognized just 28 percent of childhood influenza cases in hospital settings, the researchers found.

The outpatient scenario was bleaker. Children treated as outpatients were correctly diagnosed just 17 percent of the time. Thirty-five percent of infected children saw a health professional within two days of onset of the flu.

"People in hospitals have long suspected that influenza brought in a lot of young children, but what we didn't realize is the number of outpatient visits the virus creates," said Poehling.

"We went to pediatricians' offices and tested children 6 months to 5 years and found that in a moderate flu season, one in six children seen actually had the flu. It was one in 16 during a mild flu season," she added.

Treatment Minimizes Impact

Some doctors diagnosed viral infections other than flu, the study found.

Vaccination decreases the rate of infection and moderates the severity of a case of flu, as well as diminishing the likelihood that the patient will spread it to other family members, caregivers, teachers and schoolmates.

The federal Advisory Committee on Immunization Practices, which received the research findings early this year, has altered its recommendations for inoculations. ACIP formerly advised vaccinating children aged six months to 23 months every year against influenza but now recommends that the upper end of the range be extended to 5 years old.