Four members of the Calvert County family stricken by flu complications had the same H3N2 strain of the influenza A virus, Maryland health officials said Friday.

That strain is one of three seasonal varieties circulating in Maryland and nationwide, officials said. Previous testing had identified influenza A but not the specific subtype.

Lou Ruth Blake, 81, died at home March 1, and two of her children, Lowell, 58, and Vanessa, 56, who had cared for her, were hospitalized March 4 and died the next day.

A third child, Elaine, 51, who lived with her mother and had been her main caregiver, was hospitalized March 5 and discharged late Thursday, a MedStar Washington Hopital Center spokeswoman said.

A fifth family member, a sister of Lou Ruth Blake’s, is still at the hospital center but improving, the spokeswoman said.

Lou Ruth Blake had received a seasonal flu vaccination but none of the three adult children received one, Calvert County Health Officer David Rogers has said. This season’s vaccine protects against two strains of influenza A — H3N2 and H1N1 — and influenza B.

State health officials confirmed Friday, as county officials had earlier said they suspected, that the two siblings who died also had a bacterial infection with methicillin-resistant Staphylococcus aureus, or MRSA, a known and dangerous complication of influenza infection.

MRSA is a strain of a bacterium normally treated with common antibiotics in the penicillin family, such as methicillin. Antibiotic-resistant strains of the organism, however, have been turning up increasingly in places outside health-care settings.

The two siblings developed severe bacterial pneumonia, which is not uncommon in people infected with the flu virus. The flu virus weakens and damages the lungs, making the person more susceptible to bacterial infections.

The Blakes are part of a large extended family in Lusby that traces its roots back several generations. Officials said no additional related severe respiratory illnesses have been confirmed and no other similar clusters have been identified anywhere in Maryland. This year’s flu season, however, has started late; the flu season typically can last as late as May.