PROVE IT
Down with a cold? It could be two
November 28, 2009
THE CLAIM
A person can contract two colds at one time.
THE FACTS
The rhinovirus that causes most cases of the common cold comes in at least 99 strains. As a result, it has long been theorized that a person could be sickened with more than one cold strain at the same time.
But recent studies of the common cold and its behaviour in the human body have revealed some surprises.
In a study published in the journal Science this year, a team of researchers showed that when two strains of the virus infected a person, they could link up and swap genetic material in a process called recombination, which was once thought to be impossible in the rhinovirus.
The study demonstrated that in a typical cold season, when many strains are circulating, recombination could cause new strains to emerge rapidly.
But it is not clear how often this happens. In another study published this year in PLoS One, an online open-access journal, scientists in China followed 64 children with colds and found evidence of recombination events and what they called "triple infections" – children carrying both a cold strain and other respiratory viruses, such as influenza or adenovirus. But ultimately only a small fraction carried multiple strains of rhinovirus.
On a practical level, there is no evidence that carrying two cold strains necessarily results in longer or more severe symptoms. And in fact, studies show that in up to a quarter of cases in adults, a cold infection may result in no symptoms at all.
THE BOTTOM LINE
A single person can carry multiple cold strains at one time.
The New York Times
Toronto Star
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