Colds more common than thought

The virus that causes the common cold may be more prevalent than previously thought because many young adults with the virus do not have any symptoms, a new study has found.

Students with the cold virus who have no symptoms outnumber those with symptoms by four to one, Canadian researchers say. The study authors warned that infected students who do not have symptoms could spread the virus, known as the rhinovirus, which can also cause bronchitis and trigger asthma attacks, to other people.

"A high occurrence of [symptomless] infections indicates that university students can spread infections to classmates, or individuals in the community, without knowing they are infected," one of the researchers, Andrea Granados of McMaster University in Hamilton, Ontario, said in a news release from the American Society for Microbiology.

"The virus particles can be spread by aerosols [for example, sneezing] or direct contact with [a symptom-free] individual. There is no treatment for the common cold; therefore, frequent hand-washing is important to prevent the spread of the common cold, particularly in early fall," Granados added.

How the study was done

In conducting the study, researchers from McMaster University and St. Joseph's Healthcare in Hamilton, Ontario followed 545 college students in September and October of 2010 and 2011. The prevalence of colds typically peaks in these months, the study authors noted.

The students were asked to perform a nasal swab once a week regardless of whether or not they had any cold-like symptoms. If the students experienced symptoms, they were asked to perform a nasal swab every day for one week.

Over the two years, the students reported 167 cold-like illnesses. Of these illnesses, the researchers diagnosed rhinovirus in 54%.

In order to figure out how many students had the virus but didn't know it, the investigators selected a 10% sampling of all the nasal swabs they collected from students who had no flu-like symptoms. After randomly selecting 25 swabs each week over the course of the study, the researchers had a total of 400 swabs. Of those, 33, or 8.25%, had the rhinovirus.

Based on their findings, the study authors projected that up to 61% of students with no symptoms of the common cold are infected with rhinovirus over the course of an eight-week period.

The investigators also found that the students with symptoms had a much higher viral load than those who didn't have symptoms. The researchers noted that larger studies are needed to confirm if having decreased amounts of the virus explains why some students do not have any symptoms of their infection.

The data and conclusions of research presented at medical meetings should be viewed as preliminary until published in a peer-reviewed journal.

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