State health officials on Sunday announced three more deaths related to the new coronavirus, increasing the total in Massachusetts to five.

All three cases are men over 70: two in their 70s, in Hampden and Berkshire Counties, and one in his 90s in Suffolk County, according to the state Department of Public Health. The Berkshire County man had an underlying health condition, but all three "were in an age group that is more likely to experience severe disease from COVID-19 regardless of prior health status," according to the state.

"I fully expect that testing will go up in leaps and bounds," Gov. Charlie Baker said Sunday.

The number of confirmed coronavirus cases jumped to 646 Sunday, an increase of 121. It's a record single-day increase for the fourth day in a row, something that was expected with an increase in testing.

The number of cases grew in nearly every county, with the biggest jumps in Suffolk, Middlesex and Essex Counties. The origins of most of the new cases are untraced.

There are 199 cases in Middlesex County, 126 in Suffolk County, 75 in Norfolk County, 60 in Essex County and 37 in Worcester County.

Speaking Sunday afternoon at Morning Star Baptist Church in Mattapan, Gov. Baker said the state's goal is to expand daily testing, which will result in more confirmed cases.

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Coronaviruses are a family of viruses that include the common cold as well as much more serious diseases. The strain that emerged in China in late 2019, now called COVID-19, is related to others that have caused serious outbreaks in recent years, including severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS). The first confirmed case of COVID-19 in the U.S. was on Jan. 21.

The disease, which apparently originated in animals, is now transferring from person to person. Its symptoms include fever, coughing and shortness of breath, and many patients develop pneumonia. There is as yet no vaccine against COVID-19 it and no antiviral treatment.

According to the CDC, the best way of preventing the disease is to avoid close contact with people who are sick, to avoid touching your eyes, nose, and mouth with unwashed hands, to wash your hands often with soap and water for at least 20 seconds, and to use a hand sanitizer that contains at least 60 percent alcohol if soap and water are not available.

To avoid spreading any respiratory illness, the CDC recommends staying at home when you are sick, covering your cough or sneeze with a tissue and throwing the tissue in the trash, cleaning and disinfecting frequently touched objects and surfaces.