Three homeless people have died in the TB outbreak involving Atlanta shelters, public health officials say.

The latest TB death occurred last week at Grady Memorial Hospital, Nancy Nydam, a spokeswoman for the state Department of Public Health, said Thursday.

She said she had no further details about this or the other TB deaths.

The number of TB cases this year involving Fulton County homeless shelters, meanwhile, has increased to 28, including two shelter volunteers.

That’s up from a total of 16 cases reported in May by the Fulton County Department of Health and Wellness.

The Department of Public Health last week sent a letter to churches whose volunteers serve in homeless shelters, urging that the volunteers be screened for TB.

This TB strain is resistant to the drug isoniazid, but is curable with other anti-TB medications.

Many major cities in the past have seen TB outbreaks among their homeless populations, according to state Public Health officials.

TB is spread through the air from one person to another. The TB bacteria are dispersed into the air when a person with the disease of the lungs or throat coughs, sneezes, speaks or sings. People nearby may breathe in these bacteria and become infected.

The U.S. rate of TB has been declining. Georgia’s tuberculosis rate has also been dropping, but is still higher than the national average.

The CDC, in response to a Public Health request in May, deployed a team of epidemiologists to assist with the investigation of the TB outbreak. And the federal health agency has assigned a public health official who is currently working with the Georgia TB program.

The Georgia Public Health letter to churches, dated Aug. 1, noted that volunteers who get TB could potentially infect their own family members, friends and co-workers, “especially where there is prolonged close contact, typically several hours and usually in a poorly ventilated area.”

Dr. Patrick O’Neal, director of health protection for Public Health, said in June that the homeless are “an extremely vulnerable population.”

O’Neal said homeless shelters typically “have very poor sanitation and infection control measures.’’ And the “overflow facilities’’ that take in the homeless don’t have to abide by city requirements for shelters, he added.

Last winter was unusually harsh in Georgia. O’Neal told GHN that those cold conditions may have helped increase the TB cases this year by forcing more homeless people to congregate in shelters.

The major outbreak of tuberculosis that has struck Atlanta homeless shelters this year actually began in 2009. This year’s shelter cases have the same genetic makeup identified in 2009 in four homeless TB cases, O’Neal said.