Of more than 4.4 million workers tested for cocaine across the United States in the first six months of the year, only 0.58 percent returned positive samples, an ongoing study conducted by Quest Diagnostics to track cocaine usage among US workers showed.
"Workplace drug testing is apparently a deterrent to workplace drug use in the United States," Wendy Bost, a spokeswoman for Quest, told AFP by telephone.
The results of the study showed a 15.9 percent fall from the number of positive tests returned during the whole of 2006 and were the lowest rate of positive tests since 1997, when Quest Diagnostics began compiling twice-yearly reports on cocaine usage in the US workforce.
Last year, 0.72 percent of nine million tests carried out on the general workforce came back positive for cocaine usage.
Drug use in the workplace costs US employers approximately 81 billion dollars a year in lost productivity, Quest says on its website, citing the US Department of Labor.
US-based workers in so-called safety-sensitive professions, such as pilots, bus and truck drivers and workers in nuclear power plants, are obliged by the Department of Transportation or the Nuclear Regulatory Commission to undergo drug tests.
Positive cocaine tests among the "safety-sensitive" professions fell to 0.46 percent in the first six months of the year from 0.58 percent for the whole of the previous year.