CENTRAL FALLS — Health officials yesterday were finishing up collecting the results of tuberculosis testing on 400 students from Central Falls High and figures will most likely be available today, according to a spokeswoman from the Department of Health.

“We’re hoping to tally the results by Friday. That will tell us how many positive results, but that does not mean that it’s active TB,” said Annemarie Beardsworth, spokeswoman for the Department of Health.

Tuberculosis testing began Tuesday. The PPD skin test involves injecting a small amount of fluid under the skin on the forearm and checking for results two days later. A person who has been exposed to TB will get a bump on the pricked area. The test may cause redness or swelling, but that doesn’t necessarily mean a positive result. A nurse or doctor needs to measure the size of the bump to determine whether the test is positive. The skin tests will be repeated in 10 weeks because a person recently exposed to TB may not test positive for several weeks.

When exposed to TB, most people’s immune systems mount a defense that prevents the bacteria from multiplying or spreading. These people have “latent TB”; they don’t get sick and are not contagious. About 300 to 400 cases of latent TB are identified in Rhode Island each year.

When the person’s body cannot fight the tuberculosis bacteria, the person has symptoms and can be contagious, which means it’s an active case. Beardsworth said that latent TB can be treated by taking medication every day for a nine-month period. Active TB, depending on the individual, involves taking multiple medications for about six months depending on how the person responds to treatment, she said.

Anyone with positive results will be referred to the RISE clinic, the state-supported TB specialty clinic at 14 Third St., Providence, for further medical evaluation and, if necessary, treatment.

Supt. of Schools Frances A. Gallo said that there are 30 students on record at the high school as having latent TB. These cases were already on record before the latest incident in which a student with active tuberculosis was found to have been attending school for some time. The student had told health officials that he had had symptoms for some time but not bad enough to stay home from school.

Tuberculosis is a bacterial illness that spreads though the air when an infected person coughs, sings or speaks. Breathing air with TB can lead to infection. But TB does not live for very long outside the body, is killed by sunlight, and is not spread through ventilation systems. It also does not spread through food. It cannot be picked up from surfaces that an infected person touched, such as drinking glasses, eating utensils, cell phones or keyboards.

Gallo said that public discussion of tuberculosis and its treatment has brought forward some adults who know they are infected with tuberculosis and who now see that it is treatable.

“People are understating that it’s completely treatable. There are a few parents who said I went for the test. I was pleasantly surprised that the stigma of fear is gone. We’ve done a good job through the press and in collaboration with the Health Department to let people know that this is treatable,” Gallo said.

tpina@projo.com