The markets have begun to pop champagne over global economic recovery, but the elephant lurking in the room -- swine flu -- could trample those green shoots.
Spotted just four months ago, the new A(H1N1) influenza virus spread by June into a global pandemic and experts warn it could take a toll on productivity and financial systems, depending on the severity of outbreaks.
About 1,800 people have died in the pandemic that now affects more than 170 countries, according to the World Health Organization.
Though the number of cases reported to WHO has topped 182,000, the United Nations health watchdog cautions the real number is higher because countries are no longer required to test and report individual cases.
Health officials are gearing up for a resurgence in cases as the northern hemisphere enters winter. So far swine flu infections generally have been relatively mild, with typical flu symptoms that last about a week.
However, the pandemic virus could mutate into a more deadly form. Officials are projecting a shortfall in vaccines being rushed to market in hopes of warding off a potential global health disaster.
Faced with the unpredictable nature of flu viruses, economists say it is difficult to assess the impact of swine flu on the delicate global economic recovery taking shape amid the worst world recession since World War II.
Will the elephant leave the party quietly or run amok?
"As the severity of A(H1N1) is so far not severe, we would not expect the magnitude of the shock to the economy to be large relative to GDP (gross domestic product)," said Simonetta Nardin, a spokeswoman at the International Monetary Fund.
"The main threat to financial stability is the risk that high levels of absenteeism could lead to breakdowns in the functioning of key financial systems," she said.
School closures would exacerbate absenteeism, further reducing workplace productivity.
Nardin said that the effects of swine flu on global financial stability and the world economy would be covered in future updates of the IMF's Global Financial Stability Report and World Economic Outlook (WEO), "as warranted by events."
World Bank experts have estimated the potential economic costs of a global influenza pandemic could range from 0.7 percent to 4.8 percent of global GDP depending on the severity of the outbreak.
The lower estimate was benchmarked on the Hong Kong flu of 1968-1969, while the upper bound was based on the devastating 1918-1919 Spanish flu, which infected an estimated one third of the world's population and caused 50 million deaths.
Based on the IMF estimate of 2009 global GDP of 54.863 trillion dollars, the swine flu pandemic, using the World Bank simulation, could cost the global economy between 384 billion dollars and 2.633 trillion dollars.
"In the case of a serious flu, 70 percent of the overall economic cost would come from absenteeism and efforts to avoid infection," World Bank experts wrote in the Global Development Finance report released in June.
"Generally speaking, developing countries would be hardest hit, because higher population densities, relatively weak health care systems, and poverty accentuate the economic impacts in some countries."
The swine flu virus was first identified in California in late April and officials linked the new virus to an outbreak of illnesses in Mexico.
Mexico has borne the brunt of the economic costs of the epidemic, particularly in the transportation and tourism sectors.
"While we expect these effects to dissipate quickly following the peak of the epidemic in May, we estimate that the swine flu epidemic will have lowered GDP growth in Mexico on the order of 0.5 to 1.0 percent in 2009," an IMF official said, on condition of anonymity.
"These effects are already factored into our baseline outlook for growth in Mexico of negative 7.3 percent in 2009, as released in the July 2009 WEO," the official said.