Tuberculosis: an Ancient Disease but a Modern Day Problem

World Tuberculosis Day, observed annually on March 24, commemorates the identification by Dr. Robert Koch of Mycobacterium tuberculosis, the bacillus that causes tuberculosis. When I tell people I work in the field of tuberculosis research, they are often surprised because they think of it as an ancient disease that no longer exists. And yes, tuberculosis is an ancient disease, but sadly it continues to be a very current problem.

When I tell people I work in the field of tuberculosis research, they are often surprised because they think of it as an ancient disease that no longer exists. And yes, tuberculosis is an ancient disease, but sadly it continues to be a very current problem

Although the bacteria that causes tuberculosis was discovered only 140 years ago, the disease has been known for thousands of years. In 2020, it caused approximately 10 million cases and was responsible for 1.5 million deaths. Despite these unacceptably high figures, the disease is treatable and in countries that have the necessary resources, it can not only be cured but also detected in time to contain community transmission. This is why the incidence is currently so low in high-income countries, such as Spain.

However, the fact that case numbers are low in affluent countries does not mean that tuberculosis is a thing of the past on a global scale. As so often happens, we tend to forget that there are countries where this disease continues to cause untold damage. In fact, until the COVID-19 pandemic, tuberculosis was the disease caused by a single infectious agent responsible for the most deaths worldwide.

Until the COVID-19 pandemic, tuberculosis was the disease caused by a single infectious agent responsible for the most deaths worldwide

Precisely because of the great risk it poses, tuberculosis is a notifiable disease subject to close global surveillance by the World Health Organisation (WHO). Monitoring tuberculosis presents multiple challenges, however, due to the heterogeneity of the resources available in different countries and the strategies they use. An additional problem is the difficulty of detecting the disease in certain vulnerable groups (for example, children and people living with HIV/AIDS). As a result, differences can be seen in annual WHO tuberculosis reports between the number of cases reported and the estimated number of people with the disease worldwide (including undiagnosed and/or unreported cases).

As a result of global efforts to improve reporting and diagnostic tools, the annual number of cases reported rose from 5.7-5.8 million in the period 2009-2012 to 7.1 million in 2019. Since the estimated incidence of tuberculosis during that period remained relatively stable at 10 million cases per year, the number of unreported and undiagnosed cases fell from 4.2 million to 2.8 million over the 10-year period.

Global Advances in the Fight Against TB at Risk

In the aftermath of the COVID-19 pandemic, we have seen a sharp decline in reported cases of tuberculosis. According to the latest WHO report, the estimated number of unreported (probably undiagnosed) cases rose to 4.1 million in 2020, a return to levels not seen since 2012.

In the aftermath of the COVID-19 pandemic, we have seen a sharp decline in reported cases of tuberculosis. According to the WHO, the estimated number of unreported (probably undiagnosed) cases rose to 4.1 million in 2020, a return to levels not seen since 2012

In addition to this drop in notifications, the pandemic also gave rise to a decline in treatment coverage, which fell from 72% in 2019 to 59% in 2020, posing a health problem not only for people with the disease (who are likely to die without treatment) but also to those around them because of the increased chances of contagion.

Although it might be assumed that the measures taken to slow the spread of COVID-19 would also reduce community transmission of tuberculosis, this does not appear to have been the case. COVID-19 restrictions were imposed only intermittently and patients with tuberculosis remain infectious and can transmit the disease over a long period of time. Short-term restrictions would not, therefore, lead to a very marked decline in cases, especially if diagnosis and notification were reduced during the pandemic. Furthermore, the decrease in reported cases occurred in March 2020, right at the start of the pandemic restrictions. Given the long incubation period of tuberculosis, a decline in notifications would only have been observed months later. Thus, the immediate reduction in notifications supports the thesis that the decline was due to underdiagnosis.

In addition to strengthening notification strategies, research on diagnostic tools is vital. We need to develop more sensitive methods for detecting tuberculosis as well as tests that are more accessible, economical and easy to perform in low-resource settings.