Flu project reveals “large invisible iceberg” of disease

Preliminary findings from a multi-million dollar, five-year international flu study reveal the extent to which people are infected by influenza viruses.

The new data, generated from the Southern Hemisphere Influenza and Vaccine Effectiveness Research and Surveillance (SHIVERS) study shows that about one in five people were infected with influenza, with even higher numbers for young people under 19 (one in three). Over 70% of those infected with influenza did not have flu symptoms, and of those with symptoms, 80% did not visit a GP.

From the New Zealand Herald (read in full here):

“For participants who had a cough and fever, a nose or throat swab was taken and tested for viruses that cause the flu or other respiratory infections.

“The study indicated that of an estimated 840,000 people infected with flu, 220,000 became sick with flu symptoms and 28,000 made a GP visit.

“Nearly 1700 people would have been hospitalised with flu, including 63 admissions to hospital intensive care units, and 22 deaths.

“Huang said while it was known that in influenza and many other viruses people could be infected without feeling ill, the sheer proportion of those who were asymptomatic caught her and her colleagues by surprise.

“It showed us that if we are only looking at those who get hospitalised or go to the doctor, we are only picking up the tip of the iceberg: there’s a big part of it that has never been seen before, and through this survey, we’ve shown it’s a fairly large proportion.”