It's estimated the direct and indirect costs of colds in the United States add up to $60 billion US.

Scientists who've decoded the genetic instruction manual for 99 known strains of the common cold virus say they have discovered a shortcut in the life cycle, but it's unlikely a single drug will help.

Common colds, or rhinoviruses, spread quickly between victims, usually leaving sniffles and coughs in their wake.

"We generally think of colds as a nuisance, but they can be debilitating in the very young and in older individuals, and can trigger asthma attacks at any age," said study author Dr. Stephen Liggett of the University of Maryland medical school,

The study appears in Thursday's online issue of the journal Science.

Subgroups of rhinoviruses have different genetic makeups, Liggett said, adding "that probably is going to mean that we may need three or four drugs."

Cold viruses sicken children on average 10 times a year and adults at least twice a year on average. The researchers estimated the direct and indirect costs of colds in the U.S. add up to about $60 billion US annually in lost wages, health care costs and purchases of over-the-counter cough and cold medications.

New approach for therapies

Rhinoviruses themselves have a single gene that codes for a protein. The protein is activated once it is broken up into 11 smaller pieces by an enzyme called a protease.

Previously, researchers have tried to tackle the large protein, but the virus simply mutated to avoid it. The viruses are promiscuous in swapping genetic material to change and adapt.

Liggett's team found that rhinoviruses take a shortcut in making the protein by skipping a step, which may speed up their knack for making victims feel lousy soon after infection.

"We would not have had any sort of intuition about this had it not been revealed through genome analysis," said co-investigator Claire Fraser-Liggett, director of the Institute for Genome Sciences and professor of medicine and microbiology at the University of Maryland School of Medicine.

"Information that comes from this discovery might present a completely different approach in terms of therapy."

Attacking the protease could be a more fruitful strategy for drug designers.

Costly cure

But if multiple drugs are needed, then people with colds would need to go to a doctor for testing to determine what rhinovirus is behind their symptoms, adding costs to the health care system.

"To add hundreds of dollars to the medical budget for really no benefit is a tough sell, even if we had such a perfect drug available," said Dr. Aaron Glatt, a spokesperson for the Infectious Diseases Society of America who is an infectious disease physician in Long Island, N.Y.

"Until you come up with a very, very simple treatment, you're not going to go anywhere with it .… It's going to always be the poor orphan in terms of research. It's going to be the poor orphan in terms of public health support for it."

The researchers plan to try to match viruses to illnesses in the hopes of determines whether some rhinoviruses are worse than others

They are also working on comparing sequences from across the U.S. today compared to those collected decades earlier, to learn more about how quickly the viruses mutate.

The research was done without external funding.

With files from Canadian Press