Eleven cases of influenza have been detected in pigs that were shown at the Great Frederick Fair in Frederick County, Md., and all swine at the county fairgrounds have been placed under quarantine, the Maryland department of agriculture said Sunday.

The pig quarantine in Frederick follows by a few days the Sept. 19 quarantine imposed by the agriculture department on swine at the Charles County, Md., Fair. Five cases of flu were detected in pigs that were recently exhibited at the Charles County, the state health department said.

In addition, the health department said influenza virus had been found in seven Maryland residents who had close contact with pigs at the fair there. It identified the strain of flu found in the seven residents as H3N2v. A similar strain of influenza A was found in the infected pigs in Charles County, according to the agriculture department.

The flu detected in the pigs in Frederick County was identified as influenza A by the health department, but it was not clear which strain of the virus was involved.

None of the seven had been hospitalized or developed serious illness.

Flu viruses do not affect safety in pork that has been properly cooked, the department said.

The flu detected in the pigs in Frederick County was identified as influenza A by the agriculture department, but it was not clear which strain of the virus was involved.

The department said last week that it had shut down prospective swine activities at the Calvert and St. Mary’s County fairs.

A D.C. state fair, which is run by a volunteers in a nonprofit organization was held on Sunday, but no swine problems were reported.

Jenn Nichols a spokeswoman for the D.C. fair said “we had no livestock.” The fair did include a pet parade. But livestock were not in it, she said.