Health workers wear face masks to guard against swine flu at a hospital in El Salvador's capital, San Salvador. More than 700 people have died of swine flu worldwide, five of them in El Salvador. (Luis Galdamez/Reuters)

The World Health Organization said Tuesday that the number of deaths globally from the H1N1 virus has doubled in the past three weeks, rising to over 700 from about 330 at the start of July.

The UN health agency gave no breakdown of the deaths. Last Friday, it said maintaining an accurate count of those who have been infected has become impossible because of the speed at which the virus is spreading.

The organization recently recommended governments stop tallying the number of H1N1 flu patients nationally.

As of last week, Canada was reporting more than 10,000 swine flu cases, with 45 deaths. Between 4,000 and 8,000 Canadians die of influenza and its complications annually, depending on the severity of the season, the Public Health Agency said.

Worldwide, the number of deaths related to seasonal flu is between 250,000 and 500,000 annually.

About 125,000 laboratory-confirmed cases of swine flu have been reported around the globe since the disease was first reported in Mexico in April, but it's thought the number of actual cases far exceeds that.

While the number of deaths is small compared to seasonal flu, the impact from the rapid spike in cases this month is being felt worldwide.

Religious leaders have been drawn into the debate after authorities in Jordan and health officials at a conference in Saudi Arabia recommended that people thought to be most at risk, including pregnant women and those with chronic diseases, refrain from performing the hajj pilgrimage to Saudi Arabia this year.

Weighing benefit of school closures

In an article written for the journal Lancet Infectious Diseases, British researchers said school closures may be among the most effective measures to slow the spread of swine flu.

Lead researcher Neil Ferguson, an epidemiologist at London's Imperial College, said the measure would give health officials time to prepare for what's expected to be a more serious pandemic in the fall.

However, the researchers also said health officials must weigh the potential health benefits of reducing transmission against "high economic and social costs, difficult ethical issues, and the possible disruption of key services such as health care."

WHO spokeswoman Aphaluck Bhatiasevi agreed that closing schools is one option that countries may consider. But she said governments will face different levels of the pandemic at different times, and must decide what measures best suit their situation.

In the past, flu viruses have taken at least six months to spread as widely as the H1N1 virus has in less than six weeks.

Despite the rise in cases, the WHO is also saying the flu caused by H1N1 is generally mild. Most patients recover within a week and do not require medical treatment.

With files from The Associated Press