Tuberculosis is not a forgotten disease – it still remains a dangerous infectious disease all over the world. In Poland, 2018 were registered in 5. 487 cases caused by Mycobacterium tuberculosis. How is tuberculosis diagnosed and how is it diagnosed? Prof. Zofia Zwolska, an expert in the field of tuberculosis and mycobacteriosis.
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Professor, recently, when we think about infections, we mainly focus on COVID-19, forgetting about other infectious diseases. Do you also have this feeling? How has the emergence of a new pathogen in the form of the SARS-CoV-2 virus influenced the diagnosis of tuberculosis?
Prof. dr hab. n. biol. Zofia Zwolska – microbiologist, long-term head of the Department of Microbiology of the National Reference Laboratory of Tuberculosis at IGiChP in WarsawIn the first decade of 2020, when the WHO announced the threat of a COVID-19 pandemic to the world, all health care efforts were suddenly directed to diagnosing the virus and developing ways to protect people from the spread of infection. Faced with the new threat, all other health problems, including infectious diseases, have been marginalized. Research laboratories focused on developing diagnostic methods for the new virus, doctors saved patients. Patients with other infectious diseases were not taken care of, and their care was postponed until the “pocovid” period.
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Denying hospitalization to patients with multi-drug resistant tuberculosis, such as MDR, and thus delaying the start of treatment – as is the case in some countries – may result in a very dangerous health situation in societies. I heard the opinions of experts that the efforts of research teams dealing with tuberculosis (in various aspects) will be stunted for years. Let us not forget that there are diseases that spread all over the world. Tuberculosis is one of them.
I remember that in 2017, tuberculosis was recognized as one of the four most serious diseases threatening humanity at the European Congress of Clinical Microbiology and Infectious Diseases. Is tuberculosis such a serious problem in Poland?
Tuberculosis, one of the oldest infectious diseases in human history, is still among the diseases that kill the most people in the world. In Poland, cases of tuberculosis are registered in the National Tuberculosis Register (KRG) kept by the Institute of Tuberculosis and Lung Diseases in Warsaw.
Generally speaking, the incidence of tuberculosis has been decreasing in Poland for several decades with different dynamics. In 2018, 5 jobs were registered in Poland. 487 cases of tuberculosis, which is 300 cases less than in the previous year. As in other countries, the most common form of tuberculosis was pulmonary tuberculosis. The greatest number of cases was recorded among people aged 45-64 (45,5%). Cases of tuberculosis in children up to 14 years of age accounted for 1,2 percent. in general.
Who should be tested for tuberculosis?
The main group are people who are concerned about symptoms such as prolonged cough not disappearing after treatment, general weakness, low-grade fever, night sweats, loss of appetite, and sometimes blood-stained sputum. Such symptoms are a signal to see a doctor. The family doctor orders tests and refers the patient to a pulmonologist who conducts further diagnostics, starts and supervises the treatment, confirms recovery and termination of treatment. Another group is “contact people” who in their environment – in their family, work, place of study – had contact with a person diagnosed with tuberculosis.
What diagnostic methods are used to diagnose tuberculosis? What’s the gold standard?
The same diagnostic algorithm recommended by WHO is adopted in all countries of the world. When tuberculosis of the respiratory system is suspected, the panel of necessary tests includes: medical history and physical examination, chest X-ray, OT (tuberculin test), possibly IGRA tests, blood chemistry and microbiological tests.
Microbiological diagnosis of a person suspected of having tuberculosis is one of the most important. When tuberculosis mycobacteria are detected in the laboratory, it is a certain confirmation of the disease process, and the drug susceptibility test performed is an indispensable clue for treatment. Microbiological testing is the gold standard in the diagnosis of tuberculosis. Moreover, the microbiological examination confirms the disinfection of the patient and the effectiveness of the treatment.
Let’s focus on laboratory research. The microscope preparation is one of the oldest methods among microbiological tests. Why is it still so important in the diagnosis of tuberculosis? What is the best staining of the preparation?
In the microbiological panel, the first basic test is a slide smear and microscopic examination of the fuchsin-stained smear according to the Zhiel-Neelsen (ZN) method. It is the only method specific for acid-fast mycobacteria.
Microscopic examination enables:
- detection of mycobacterial diseases
- with clear clinical symptoms, it allows treatment to be started
- points to the need to isolate the suspect of the disease
- allows you to track the dynamics of debondification
- confirmation of the patient’s recovery
Many international experiences, including Polish ones, show that after detection of mycobacteria with the ZN method, a molecular test should be performed to confirm whether the mycobacteria observed in the microscope definitely belong to the complex mycobacteriumtuberculosis, and they do not constitute environmental pollution, e.g. with acid-fast saprophytes.
Why is the culture of patient material on special media the gold standard in tuberculosis diagnosis in Poland? In many countries, such standards do not apply.
I do not know any countries where there is no obligation to culture diagnostic materials from patients. If done, these are local savings recommendations because of misconceptions about the value of microbiological testing for tuberculosis. The first test, which is microscopic examination, has high specificity and low sensitivity. Mycobacteria in a smear are detected when there are at least 1 thousand sputum in 10 ml of sputum. mycobacterial cells. When we inoculate the media, we can obtain cultures when there are only about 500 mycobacterial cells in the material from the patient. Colonies emerge after about 3-4 weeks of incubation.
What is the advantage of the automatic method over the manual method when it comes to culture?
In automatic methods, the cultivation takes place on liquid media, which allow mycobacteria easier access to nutrients and accelerate their growth, reducing the time of mycobacteria reproduction up to 5-7 days. Especially valuable are cultures for liquid media from materials collected from patients suspected of extrapulmonary tuberculosis.
Now I will ask about one of the most modern methods in diagnosing tuberculosis. How valuable is genetic research? When should they be performed?
Genetic tests accelerated the process of diagnosing patients, reducing the time to 1-2 days and significantly increasing the detection rate – even up to 98%. One should always remember about the presence of genetic reaction inhibitors, which are included in the diagnostic material and may hinder the detection of mycobacterial DNA. In closed automatic systems, it is possible not only to detect the genetic material of mycobacteria from the tuberculosis complex, but also to obtain information about drug resistance. In the laboratory algorithm, genetic methods are essential and occupy a significant place, but they do not release the obligation to inoculate the media.
Tuberculosis is not the only disease caused by mycobacteria. Can you, professor, introduce us to the concept of mycobacteriosis?
In laboratories, mycobacteria are grown from materials collected from patients, also mycobacteria mycobacteria other than tuberculosis, historically called atypical mycobacteria. They are ubiquitous in the human environment, and their main source is water and soil. It is the responsibility of each laboratory to identify mycobacteria grown and to distinguish between atypical and atypical mycobacteria. Such information should be passed on to the doctor. The basis for the diagnosis of mycobacteriosis is the multiple isolation of MOTT mycobacteria belonging to the same species. If in doubt, the case should be consulted with the DPRK.
The interview was conducted by Elwira Zawidzka, medical microbiology specialist, laboratory diagnostician and product manager for microbiology ALAB laboratories
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