Two rare HIV strains were snared recently during routine testing in Maryland, news that raised goosebumps in summer headlines but that the FDA dismissed as "no cause for alarm." The strains-Group M (subtype G) and Group O-showed up in the blood of two hetero women believed to have gotten the virus in Africa. Because Group M is common-99 percent of Americans with HIV are infected with M (subtype B)-G is likely to be prey to available tests and treatments. But O is trickier: Liza Solomon, director of the Maryland State AIDS Administration, said O viral load measurements may be ambiguous; and Patrick Sullivan, a CDC epidemiologist, echoed these concerns. "The tests screening subtype B approach 100 percent accuracy. That falls to about 80 percent with Group O." He added that nukes such as AZT may be less effective against O. The FDA has urged the CDC and HIV-test-kit makers to "find ways to improve detection of O," said Sullivan. The feds temporarily restricted blood donations from people born in O-identified parts of Africa. Several hundred cases of each oddball strain have been reported worldwide.