Health officials say a fourth person has died from swine flu in Marin County.

County health officers say the 71-year-old man who died Thursday had pre-existing medical conditions that made him vulnerable to the H1N1 virus.

Officials would not say what those conditions were, which hospital the man died at or in what city he lived.

Marin County's other swine flu victims include a 55-year-old man from San Rafael, a 33-year-old pregnant woman and a 78-year-old man.

Anju Goel, the county's deputy public health officer, say there have been 35 confirmed and 70 probable cases of swine flu in Marin.

But officials suspect there have been many more cases because tests to confirm swine flu are only performed in special circumstances.