Highly contagious tuberculosis still a threat worldwide; 10M infected yearly

DEAR DR. ROACH >> I recently read that tuberculosis kills more people than any other infectious illness. Can people who have no symptoms spread this disease?

— R.R.

ANSWER >> Tuberculosis, an ancient disease, is caused by Mycobacterium tuberculosis. It infects 10 million people per year and kills 1.5 million people yearly worldwide, mostly in Africa and India. This is more than malaria and HIV combined. Although tuberculosis was the cause of death for 1 in 7 people during the 19th century in Europe and the U.S., there were only 9,000 cases of TB and 500 deaths in the U.S. in 2017.

Most cases of tuberculosis are spread person-toperson, with the primary route being inhalation of the bacteria a person has coughed. Household contacts of an infected person are at the highest risk of acquiring tuberculosis; if infected, 90% to 95% of those will successfully control the bacteria and enter a latent phase of infection, which has no symptoms. However, in 5% to 10% of those people, the bacteria will become active and cause clinical infection. Cough, fever, night sweats and weight loss are classic symptoms of active tuberculosis infection. Reactivation of tuberculosis is most likely to happen in the first two to three years after exposure, but may also happen if a person’s immune system becomes weakened due to serious illness or medication that suppresses it.

Only people with active tuberculosis infection can spread the disease. Latent disease cannot be spread. Cough is the most effective means of expelling tuberculosis, but recent research suggests cough is not necessary for tuberculosis to spread.

Quick identification and quarantine of people with tuberculosis and rapid treatment are the keys to preventing its spread.

Since tuberculosis is much less common than in the past, physicians need to be aware that this disease is still prevalent, and we need to be diligent about considering the diagnosis.

Contact Dr. Roach at ToYourGoodHealth@med. cornell.edu.