March 24 is World Tuberculosis Day, marked each year to raise public awareness about the devastating health, social and economic consequences of tuberculosis (TB) and to step up efforts to end the global TB epidemic. World alertness to it has been lessened by COVID-19.

TB is a contagious, airborne disease caused by bacteria (Mycobacterium tuberculosis) that most commonly affects the lungs. TB infects over 10 million people worldwide every year. Today, TB is the second-leading infectious global killer after COVID-19 (above HIV/AIDS). When people with lung TB cough, sneeze or spit, they propel TB germs into the air. A person needs to inhale only a few of these germs to become infected.

TB is a significant infectious disease in Hong Kong. Every year, there are about 4,500 notified cases of TB. About 1 out of every 20 people in Hong Kong will develop TB during some time in their life.

Over the last 30 years, China has significantly reduced TB incidence and the death rate, but hundreds of thousands are still infected.

Tobacco and TB

Tobacco smoking has been suspected to be a risk factor for TB for more than a century, but only recently has consistent epidemiological evidence between tobacco and TB been established.

Even this strong association between tobacco use and TB had been largely neglected despite, or perhaps because of, the fact that TB currently affects the poorest, least-educated and most-illiterate people.

Tobacco users are more likely to be infected with TB, to progress to active disease and to die from TB. Smoking is also associated with delayed diagnoses, more severe disease, unfavorable treatment outcomes, and relapse after treatment. These effects appear to be independent of the effects of alcohol use, socioeconomic status and a large number of other potential confounders.

Several major studies by the University of Oxford in India and China illustrate this strong association between tobacco use and TB deaths. A study of 80,000 people in India showed that smokers were four times more likely to die of TB than nonsmokers. Men in urban China smoking more than 20 cigarettes a day had doubled the death rate from TB of nonsmokers.

The age factor: It has been known for a long time that smoking causes lung cancer and heart disease. But one big difference in the link between smoking and TB is age. While cancer and heart disease are commonly associated with older smokers, TB primarily affects young, working-age people, with an economic impact on the patient, their families and their employment.

Looking into the future, most new TB cases will be in Africa, the eastern Mediterranean and Southeast Asia — all big tobacco markets. It has been predicted that 40 million smokers could die from TB by 2050.

There are several mechanisms as to how the whole spectrum of tobacco products, including cigarettes, e-cigarettes and heated tobacco products, causes such harm in TB patients, which include: direct damage to the lungs decreases the resistance of the lungs to infection, particularly by the TB germ; tobacco impairs the normal clearance of secretions on the surface of the air passages to the lung, allowing the TB germ to escape the first level of host defenses, and pass deep inside the lung; smoke and nicotine impair the function of pulmonary alveolar macrophages, which are an important early defense mechanism against the bacteria; and smoking impacts the body’s immune system, making smokers more susceptible to TB infection.

The tobacco industry

Throughout the last half-century, the tobacco industry has denied the health harm of active and passive smoking. The industry has portrayed low-tar cigarettes and filter cigarettes as safer products, and even now claims the new tobacco products as safe alternatives to traditional, combustible cigarettes.

TB patients may be misled into changing to these products. Many people mistakenly believe smoking filtered cigarettes is safer than smoking nonfiltered cigarettes. Filtered cigarettes are no safer than nonfiltered. Filters do not protect smokers from the harmful chemicals in tobacco and, in some ways, they may be more dangerous than nonfiltered cigarettes. In particular, there is no evidence that smoking filtered cigarettes protects TB patients against the serious additional effects of smoking, or protects nonsmokers against the harm of secondhand smoke. Filtered cigarettes are not the answer for TB patients who smoke.

Quitting

Because tobacco worsens TB in all the ways described, the World Health Organization advocates that, in addition to TB treatment, smoking-cessation strategies should be part of all TB control programs. The WHO has produced guidelines to help TB patients quit smoking, and a toolkit specifically aimed at helping TB patients quit smoking. The WHO reinforces this with health promotion messages:

“You are not just a smoker; you are a smoker with TB.” “It is important that you quit now.” “Cutting down while you are having TB is not enough.” “Quitting may dramatically improve the lasting success of your TB treatment.”

The WHO reminds smokers of the benefits of quitting while diagnosed with tuberculosis: Reduced severity of TB symptoms; less drug resistance; reduced probability of recurrent TB; reduced chance of dying from TB; reduced risk of spreading TB to others; and a reduced risk of exposure to tobacco smoke by nonsmokers, which will also significantly reduce the risks of others being infected with TB.

One of the most important decisions if you are a TB patient is quitting all forms of tobacco use.

The author is a special adviser to the Global Center for Good Governance in Tobacco Control, a senior policy adviser to the World Health Organization, and director of the Asian Consultancy on Tobacco Control.

The views do not necessarily reflect those of China Daily.