The swine flu outbreak seems to have peaked in most of the southern hemisphere, the World Health Organization said in a statement on its Web site today.

Chile, Argentina, New Zealand and Australia "appear to have passed their peak of influenza activity," according to the statement. South Africa and Bolivia are still seeing higher levels of flu than normal, the Geneva-based United Nations agency said in its weekly update on the spread of the virus.

In North America, Europe and Central Asia, flu activity remains low, with some countries experiencing localized outbreaks, according to the statement. Countries in the northern hemisphere, where the flu season gets under way in the fall, are being advised to prepare for a second wave of pandemic spread, the WHO said in a separate report today.

The "overwhelming majority" of patients continue to experience mild illness, and there's no sign that the virus has mutated into a more virulent form, the agency said. The virus, which is also known as H1N1, is now the dominant influenza strain in most parts of the world, the WHO said.

Doctors have reported a very severe form of the disease, in young and otherwise healthy people, in which the virus directly infects the lungs, causing respiratory failure, according to the WHO. Specialized treatment with long stays in intensive care units is needed for those patients, and ICUs may be overwhelmed by a sudden surge in such cases, according to the report.

The number of swine flu cases globally reported to the WHO totaled more than 209,000 as of Aug. 23, with at least 2,185 deaths, the agency said. Countries no longer are testing and reporting individual cases, so the statistics understate the actual number of people who have contracted the virus, the WHO said.

Tropical regions, including Central America and parts of Asia, are seeing "increasing or sustained high levels" of the virus, the WHO said.