Tuberculosis Can Spread Before Sufferers Realise It

The hallmark of tuberculosis (TB) has long been identified through a cough that lasts for weeks, is deep, and rasping. Logically, patients who do not cough are considered unlikely to transmit the disease. However, a recent study warns that many TB sufferers never experience a chronic cough or other typical symptoms, yet can still spread the bacteria to those around them.

Until now, TB control programmes have relied heavily on symptom-based screening, particularly coughing. Consequently, people who feel healthy tend to slip through testing and their infections go uncounted. In fact, the majority of TB cases in the community do not present symptoms, a condition known as asymptomatic TB.

To test whether these asymptomatic patients can transmit the bacteria, researchers monitored household members of TB patients at four health centres in eastern China. The study involved a public health team in Jiangsu Province working with international collaborators, including Dr. Leonardo Martinez, an epidemiologist from Boston University (BU).

The team tracked more than 1,000 close contacts living in the same house and 560 neighbours with no history of exposure. They were tested using QuantiFERON, a blood test to detect immune response to TB bacteria, as well as skin tests.

The results were striking and remarkably clear. The proportion of close contacts infected with TB bacteria was nearly identical, whether the patient in the household had obvious symptoms or was completely asymptomatic. About one in four close contacts showed a positive test result in both groups. This figure was twice as high compared to the group of neighbours who were not exposed within the home.

There has been a longstanding belief that a person must cough to spread TB. However, recent laboratory findings indicate that ordinary quiet breathing, known as tidal breathing, is sufficient to release bacteria into the air. A person breathing calmly across a table without coughing can still fill a room with infectious particles without any warning signs.

The study, published in the journal Nature Communications, confirms that TB patients who feel healthy are just as infectious as those who are severely ill. This reality poses a major challenge for screening programmes that rely solely on questions about cough symptoms. Finding these hidden cases requires diagnostic tools that do not wait for symptoms to appear, such as chest X-rays or broader blood testing. Furthermore, the study reinforces the urgency of providing preventive therapy to all family members living in the same household as a TB patient, regardless of whether that patient shows symptoms or not.