The tropical disease, melioidosis, is most common in Southeast Asia and northern Australia and is caused by bacteria in soil rising to the surface and mixing with water during heavy rainfall. It can contracted by inhalation, contact with contaminated soil, or drinking contaminated water. The illness causes pneumonia, fever, anorexia, muscle soreness and chest pain.
Singapore has an average of 67 cases of the disease and 12 deaths a year. But since January, there have already been 57 cases and 23 deaths, according to statistics posted on the Health Ministry's Web site.
A sudden cluster of melioidosis cases - 11 in one week - prompted officials to launch the probe to check if the disease had been used in a weapon, director of Medical Services K Satkunanantham said in a speech Thursday at the 4th World Melioidosis Congress.
But the probe found the DNA of the bacteria cells were genetically different from each other, indicating they were not prepared in a laboratory, he said.
Satkunanantham did not say why there had been a jump in deaths this year.
Singapore - a close U.S. ally - has been on high alert for terror attacks since Sept. 11, 2001, and has detained alleged Islamic militants suspected of plotting to attack military, diplomatic and commercial targets.
Melioidosis is recognized internationally as a possible bio-warfare agent. The United States earmarked US$50 million last year for research into vaccines and new treatments for the disease and other illnesses.