Health officials trying to make best use of antiviral drugs to fight the new H1N1 flu need to do a better job of tracking and treating cases quickly, Italian researchers said on Monday.

Having stockpiles of drugs does little good if people do not get them within the 24 to 48 hour window when they work best, Stefano Merler of the Bruno Kessler Foundation in Trento, Italy and colleagues reported.

Our study also highlights the importance of the early detection of cases, they wrote in the BioMed Central journal BMC Infectious Diseases.

In fact, great effort should be made in order to establish a surveillance system able to detect and treat cases as soon as possible since a delay of more than 24 hours could make both antiviral treatment and prophylaxis very inefficient.

But H1N1 swine flu has spread so fast that the World Health Organization has stopped counting cases, which in turn may encourage national health authorities to cut back on testing.

Merler's team found that if governments can track cases, quick use of drugs could help a great deal.

They said their mathematical models showed giving antiviral drugs to the elderly to protect them from infection would not save many lives, but treating younger people would.

Only three quick tests are licensed in the United States for diagnosing H1N1 flu -- one commercial test from Quest Diagnostics and two government tests.

The WHO has advised countries to stockpile enough antivirals to treat 25 percent of their populations.

These include zanamivir, made by GlaxoSmithKline under license from Biota Inc. and sold under the brand name Relenza, and oseltamivir, made by Roche AG under license from Gilead Sciences and sold under the brand name Tamiflu.

Both drugs can reduce the risk of death among people at serious risk of flu complications -- the very old, the very young, people with asthma and other chronic diseases and pregnant women. But they must be given within the first day or two -- which makes it important to diagnose people promptly.

Both can also be used to prevent infection. Most health experts say it is important to do this only for people who are both at high risk of complications and who have been in close contact with someone confirmed to be infected.

Some policies call for using these drugs as prophylactic agents in nursing homes, for example, where viruses can sweep through and kill many frail residents.

In a pandemic, with the drugs in high demand, this strategy may not save enough lives, the researchers said.

Our work demonstrates that even in countries where the antiviral stockpile is not sufficient to treat 25 percent of the population, the minimum level suggested by the WHO, it is possible to reduce morbidity and excess mortality by prioritizing the use of antivirals by age, Merler said in a statement.He said Italy, for example, only had enough drugs to treat 12 percent of its population.

Their model included data from the last three flu pandemics, in 1918, 1957 and 1968. In 1918, the virus affected more young adults and older children than usual -- just as has been seen with the H1N1 pandemic.

The only way to save lives with a small stockpile of drugs, they said, was to treat everyone who was infected, and give the drugs prophylactically to younger people.