Seven Maryland residents have contracted a strain of swine flu from infected pigs at the Charles County fair.

WASHINGTON — Seven Maryland residents have contracted a strain of swine flu from infected pigs at the Charles County fair.

The infected people had close contact with the five pigs recently exhibited at the Charles County Fair that tested positive for swine flu, the Maryland Department of Health said Wednesday. None of the infected individuals has developed serious illness or been hospitalized.

The pig infection, announced earlier Wednesday, led to a quarantine of all pigs at the fairgrounds and the cancellation of swine exhibits at two upcoming fairs in neighboring counties.

Transmission of swine flu — officially known as Influenza A — to humans is rare but possible, the health department said.

The Charles County Fair, which ran from Sept. 14 through Sept. 17, took place at the Charles County fairgrounds in La Plata, Maryland.

All pigs exhibited there are now under a quarantine order and will not be released until seven days after the last pig shows signs of illness. As a further step, Maryland Secretary of Agriculture Joseph Bartenfelder issued an order Tuesday canceling swine exhibits at the upcoming St. Mary’s and Calvert County fairs.

The health department said swine flu infections in humans can occur in people who have handled sick pigs, such as children handling pigs at agricultural fairs and workers in the swine industry. It is not yet clear the capacity in which the infected people came in contact with the pigs.

Since 2005, there have been about 400 cases of swine flu reported in humans, “which means that it’s really unusual,” said Dr. Anthony Fauci, director of the National Institute of Allergy and Infections Diseases at the National Institutes of Health, in a phone interview with WTOP.

“This is a phenomenon that occurs infrequently,” he added. “It has not led to significant public health problems, but you want to keep your eye out on it as you always do when you have these unusual infections.”

The symptoms of swine flu are similar to the seasonal flu, including fever, cough and sore throat.

The health department advised people who come down with flu-like symptoms and had contact with pigs in the last seven days to contact their health care providers. The local health department should be contacted if swine flu is suspected.

The Charles County Health Department can be reached at 301-609-6900 ext. 6025 and the St. Mary’s County Health Department can be reached at 301-475-4330.

To report sick pigs, you can reach the state agriculture department at 410-841-5810 or after hours at 410-841-5971.