BOSTON -- Two more Massachusetts deaths have been linked to the H1N1 influenza-a, or swine flu, the Massachusetts Department of Public Health said Monday. Four other Massachusetts residents have died of the virus.

A 13-year-old Worcester County resident who died last week has been confirmed to have had H1N1. He had a number of underlying health conditions that put him at greater risk of complications from the flu, the DPH said.

The state is also awaiting test results a 64-year-old Worcester County resident who died this weekend, and also had a series of underlying health conditions. The state believes that person's death will also be the result of the virus.

As of Monday, there have been more than 1,300 confirmed cases of H1N1 influenza in Massachusetts. Sixty-four percent of the confirmed cases in Massachusetts have been in people under the age of 18. Each year, seasonal influenza causes 250,000 hospitalizations and 36,000 deaths nationally.

Certain groups of people are at higher risk of complications from the flu, the DPH said. These groups, include children under the age of 2, adults over the age of 65, pregnant women and people with chronic health conditions such as asthma, diabetes and heart disease.