The highest covid-19 positive test rates recorded in the city last week came from two Dorchester zip codes, Mayor Martin Walsh said in a media availability on Tuesday.

According to data from October 4-10 posted on the Boston Public Health Commission’s website, Dorchester’s 02121 and 02125 had a positive test rate of 9.7 percent— well above the 4.4 citywide average tabulated by the city health agency.

Other Dorchester zip codes—02122 and 02124— were also higher than Boston overall at 6.3 percent. Mattapan was at 7.8 percent.

Walsh told reporters yesterday that the data gathered last week “remained at the somewhat elevated rate of activity that we’ve seen over the past few weeks in the city. The positive test rate has held steady in the city for a couple weeks at 4.1 percent.”

The Boston Public Health Commission is examining the data from Dorchester and contact tracing to see where new cases are emerging, who is impacted, and the most effective ways to intervene. BPHC analyzes data from "heat maps" to show where the cases are happening so that they can target outreach and efforts to the areas most impacted. It also considers complaints of where large groups were gathering, to choose the neighborhoods and parks targeted for outreach.

Additionally, BPHC mobilizes teams that provide safety materials and educational resources to residents and businesses in multiple languages in neighborhoods that report increased covid numbers, and encourages everyone to get tested for the virus regardless of whether or not residents have symptoms or are asymptomatic.

Since last Friday, the city recorded 98 new cases, bringing the city’s total to 18,136. There were 4 new deaths, Walsh said.

“The positive test rate went down from over 73 new cases a day to about 69 per day. The testing rate also went down slightly,” he added. “Young adults and the Latino community continue to see the highest numbers of new cases,” said Walsh, adding that the city will pump additional resources into areas with high rates.

The city has added a second mobile testing site that will be positioned at Nubian Square in Roxbury until October 24; and the CVS on Gallivan Boulevard will also offer free Covid testing beginning on Friday.