The World Health Organization issued new guidelines Friday for the treatment of swine flu. (Sang Tan/Associated Press)

Otherwise healthy people with uncomplicated illness from swine flu do not need to be treated with antiviral drugs, the World Health Organization said in new guidelines issued on Friday.

For patients with severe illness or whose condition begins to deteriorate, WHO recommends treatment with oseltamivir, sold as Tamiflu, as soon as possible.

The recommendation applies to groups at increased risk for more severe illness, such as pregnant women, children younger than five years old, and those with underlying medical conditions.

"At the same time, the presence of underlying medical conditions will not reliably predict all or even most cases of severe illness," the UN health agency said.

"Worldwide, around 40 per cent of severe cases are now occurring in previously healthy children and adults, usually under the age of 50 years.

"Some of these patients experience a sudden and very rapid deterioration in their clinical condition, usually on day five or six following the onset of symptoms."

Worldwide, most people infected with the pandemic virus continue to experience typical flu symptoms and fully recover within a week, even without medical treatment.

People should seek medical attention when these danger signs appear in someone with suspected or confirmed H1N1 infection:

• Shortness of breath, either during physical activity or while resting.
• Difficulty in breathing.
• Turning blue.
• Bloody or coloured sputum.
• Chest pain.
• Altered mental status.
• High fever that persists beyond three days.
• Low blood pressure.

In children, danger signs include fast or difficult breathing, lack of alertness, difficulty in waking up and little or no desire to play.

The agency said it was emphasizing use of the antivirals to prevent severe illness and death, reduce the need for hospitalization and reduce the length of hospital stays.

Fatalities described

When Tamiflu is not available or cannot be given, then zanamivir, sold under the brand name Relenza, may be given, WHO advised.

Also on Friday, health officials in the U.S. told reporters that swine flu is still spreading widely across the country, with 75 per cent of serious cases and 60 per cent of deaths among people under the age of 49.

A review of fatal cases worldwide associated with the H1N1 pandemic strain concluded at least 49 per cent had underlying disease.

"Two risk factors seem of particular importance: pregnancy and metabolic condition (including obesity, which has not been considered as risk factor in previous pandemics or seasonal influenza)," researchers from France's Institute for Public Health Surveillance concluded in Thursday's issue of the journal Eurosurveillance.

The data presented were from official sources, but the team said they need to be interpreted cautiously given differences in factors such as the quality of data, small numbers, and incomplete reporting.

Turkeys infected

On Friday, health officials in Chile reported swine flu has jumped to birds.

Chile's health ministry ordered two turkey farms outside the port city of Valparaiso to be quarantined after genetic tests confirmed sick birds showed a match with the subtype A H1N1 2009 strain.

"My understanding is that with the ones that were sick, it was a very mild disease," said Dr. Juan Lubroth, head of infectious diseases for the UN's Food and Agriculture Organization in Rome.

"It's significant in that we don't need to recommend any drastic measures, as far as culling the population of turkeys. Let them go through their illness and recover — seven to 10 days — and if they are sound and healthy, they could enter the food chain."

Andrea Campos, a veterinarian for the farms' owner, Sopraval SA, said the outbreak was limited to egg-laying birds, not those fattened to produce meat.

With files from The Associated Press