SAN FRANCISCO (Reuters) - Nearly 200 people in the San Francisco area have been sickened by an intestinal disease caused by the highly contagious Shigella bacteria since an outbreak began at a Mexican seafood restaurant 10 days ago, health officials said on Monday.

The outbreak, which began on Oct. 16 at the Mariscos San Juan No. 3 restaurant in San Jose, had spread across six counties and infected 182 people as of last Friday, the Santa Clara County Public Health Department said in a statement.

Many of those sickened have required hospitalization and at least a dozen were admitted to intensive care units, health officials said.

Health officials say transmission typically occurs when fecal matter enters the mouth, possibly when an infected food handler prepares meals consumed by unwitting diners. The department said it is investigating all possible sources of the contamination.

Shigella infections can trigger watery or bloody diarrhea, abdominal pain, fever and other symptoms, the department said. The bacteria is "extremely contagious," it added, urging sickened individuals to avoid going to work.

Two lawsuits have been filed over the outbreak as of last Friday, according to the Marler Clark law firm. The restaurant, which has been closed since Oct. 18, is cooperating with the department's investigation, health officials said.

The restaurant's owners could not immediately be reached for comment on Monday.

Young children, the elderly and HIV-positive individuals are more likely to suffer severe symptoms, according to the department.

Shigella bacteria cause some 500,000 cases of the diarrheal disease in the United States every year, according to the U.S. Centers for Disease Control and Prevention.

(Reporting by Curtis Skinner, editing by David Alexander)