Virginia health officials on Friday acknowledged that the state’s two confirmed H1N1 flu virus cases came from the Chesterfield and Three Rivers health districts.

The Chesterfield health district includes Chesterfield and Powhatan counties and the city of Colonial Heights. The Three Rivers district includes 10 county health departments on the Upper Peninsula and Northern Neck, including Essex, Gloucester, King & Queen, King William, Lancaster, Mathews, Middlesex, Northumberland, Richmond and Westmoreland.

In addition, two probable cases of H1N1 have been discovered in students at Washington and Lee University in Lexington. Both students had traveled to other states recently.

Nationwide, the count of H1N1 (or swine) flu virus cases is up to 141 people in 19 states, including the two in Virginia. New York, Texas, South Carolina and California have the large majority of the cases.

Officials said on Friday they continue to stress everyday precautions – washing hands frequently with soap and hot water, staying home if ill, covering coughs and sneezes and trying to maintain good overall health – as the most effective measures against the spread of the disease.

Karen Remley, the state health commissioner, said the Virginia Department of Health is working with school districts and colleges in the state to monitor the situation. Students more at risk of catching contagious diseases because of frequent travel, close quarters, many shared surfaces, and somewhat less attention to hygiene, Remley said.

Symptoms of H1N1 flu are similar to those of regular seasonal flu, and include fever, cough, sore throat, body aches, headache, chills and fatigue. Some people report having diarrhea and vomiting. The illness can exacerbate chronic medical conditions.

The virus is spread from person to person mainly through coughing or sneezing. People can become infected by touching something with the virus on it and then touching the mouth, nose or eyes. The virus is not spread through eating pork that has been properly handled and prepared.

The downtown Suffolk Wal-Mart had five pollen masks in stock on Friday afternoon. Health officials warned on Friday that masks alone do not prevent a person from catching the disease.

“Wearing a mask alone does not protect you,” said Diane Helentjaris, Virginia’s acting epidemiologist. “We don’t really know how much good those masks will be.”

Face masks generally are more effective at keeping the wearer from infecting others than at keeping the wearer from getting infected, Helentjaris added.

The Centers for Disease Control and Prevention are asking parents with children in school to begin making contingency plans for their children’s care should school be dismissed. Those plans should not include care in a large group, such as a day care, the CDC recommends. If schools dismiss, they should remain closed for up to 14 days, the CDC said. Suffolk Public Schools currently have no plans to dismiss students, division spokeswoman Bethanne Bradshaw said Thursday.