Flu Can Infect Many Without Causing Symptoms: Study | WPN World People News

Think you know who has the flu? Think again: a new study finds that three-quarters of people infected with seasonal flu and swine flu in recent years showed no symptoms.

Researchers analyzed data gathered in England during the winter flu seasons between 2006 and 2011, including the 2009 H1N1 "swine flu" pandemic.

Overall, about 18 percent of unvaccinated people became infected with an influenza virus, but only 23 percent of them went on to develop flu symptoms.

What's more, only about 17 percent of infected people became ill enough to see a doctor, the British study found. And compared with some of the seasonal flu strains, the 2009 swine flu strain actually caused much milder symptoms.

The findings suggest that relying on data about flu-related visits to primary care doctors underestimates the extent of flu infections and illnesses.

Overall, the infection rate for the winter flu seasons as calculated in the study were an average of 22 times higher than the rates recorded by standard methods.

"Reported cases of influenza represent the tip of a large clinical and subclinical iceberg that is mainly invisible to national surveillance systems that only record cases seeking medical attention," expert said.

Most people don't go to the doctor when they have flu. Even when they do consult they are often not recognized as having influenza. Surveillance based on patients who consult greatly underestimates the number of community cases, which in turn can lead to overestimates of the proportion of cases who end up in hospital or die.

Even if only mildly infectious, a large number of these people could play a major role in spreading flu each season.

Source: HealthDay News