The cases are probable but have not been confirmed.
Two of the Baltimore County cases are related. A family member had traveled to Mexico, officials said.
The third Baltimore County case involves someone who traveled to the Caribbean.
In Anne Arundel County, all three cases involve one family. They did not travel to an infected area of the world, but another family member did -- to Mexico.
Two of the cases involve students. One attended Folger McKinsey Elementary School in Anne Arundel County and the other attended Milford Mill Academy in Baltimore County.
In a letter sent to McKinsey parents Wednesday, the school district wrote, "The student, who is now recovering, has not been severely ill or hospitalized. The student has been at home for most of the duration of the illness."
The school will remain open, and the the State Department of Health and Mental Hygiene, the Anne Arundel County Department of Health and Anne Arundel County Public Schools determined healthy students are safe to go to the school. A thorough cleaning of the school was planned for Wednesday evening, and school staff is working with the Department of Health to track absences.
None of the six have had to be hospitalized and all are recovering, O'Malley said.
The definition of a "probable" swine flu case is an individual with flu-like symptoms who has a recent history of travel to an area affected by swine flu or contact with another person who has.
There have been no confirmed or probable cases in Virginia or the District, according to health officials.
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