Medics dispel the main myth about tuberculosis
Coughing has long been considered the primary mode of transmission of tuberculosis and its main symptom indicating the need for treatment. This gap in diagnosis has led to only 7.5 million of the 10.6 million people with this infectious disease knowing they have the disease. A new analysis of nationally representative studies from Africa and Asia has revealed just how common coughing is actually in TB.
A team of health professionals from the University of Amsterdam, the Amsterdam Institute for Global Health and Development (Netherlands), supported by staff from the Federal Ministry of Health in Sudan and the Ghana Health Service, examined the prevalence of subclinical pulmonary tuberculosis, that is, TB that occurs without significant symptoms and is often detected during home visits. The researchers reported their findings in an article for the international medical journal The Lancet Infectious Diseases.
From ancient times to the present day, mankind has made great progress in the diagnosis and treatment of tuberculosis . This infectious disease is caused by various species of mycobacteria from the Mycobacterium tuberculosis complex group (Koch's bacilli), is spread through the air by coughing, sneezing or expectoration of infected persons and most commonly affects the lungs. Despite breakthroughs, of the more than 10.6 million people with TB, only 7.5 million are aware of their diagnosis.
This gap is likely due to the fact that the majority of patients (estimated at 50.4% in the 1990-2019 data) lack recognizable symptoms, which most commonly include a prolonged cough, chest pain, increased fatigue and weakness, decreased body weight, fever, and sweating during sleep. And, according to the authors of the new study, in most past reviews it was coughing for at least two weeks that was the only sign of TB screening.
Meanwhile, according to a study in Zambia, 60% of TB patients did not report a persistent cough. One-third had other symptoms suggestive of TB for more than a month. Only 9% had no symptoms at all.
The authors of the paper decided to look further into how common cough is in TB patients and to examine its association with demographic characteristics, sputum bacterial analysis, and other risk factors.
Clinicians conducted a systematic review and meta-analysis of data from people who participated in national surveys (18 from Asia and 16 from Africa) from 2007 to 2019, including under the auspices of the World Health Organization. Each survey involved multi-stage cluster stratified selection, census, screening for TB in people 15 years of age and older with chest radiography, and data from symptom surveys completed by staff. If the screening results were positive, the person was sent for testing.
In total, the researchers obtained information on 602,863 participants: 357,970 (59.4%) were from Africa, 244,893 (40.6%) were from Asia, 347,034 (57.6%) were female, 305,452 (50.7%) were younger than 35 years old, and 359,126 (59.6%) lived in rural areas. Cough lasting more than two weeks was reported by only 28,834 (4.8%), less than two weeks by 78,395 (13.0%), and 495,634 (82.2%) did not report it at all.
After analyzing chest radiographs, abnormalities suggestive of tuberculosis were found in 53,404 patients (8.9%). Tuberculosis culture, the most accurate diagnostic method to date, was positive in 1,944 (0.3%) out of 602,863.
Of these 1,944 participants with TB, 796 (40.9%) reported having a cough for at least 14 days, 375 (19.3%) had a cough for less than two weeks, and 773 (39.8%) reported no such symptom.
"The adjusted proportion of subclinical TB was 82.8% in the absence of prolonged cough and 62.5% in the absence of any cough. The adjusted country-specific proportion of patients without persistent cough ranged from 59.4% in Laos to 89.7% in The Gambia; without cough, from 27.7% in Cambodia to 83.2% in South Africa," the medics elaborated.
TB without symptoms was more common in younger people, women and urban dwellers. At the same time, it was less likely to produce positive smear results: their proportion was estimated at 29.1%. Of the 796 participants with a positive TB culture result and persistent cough, 262 (32.9%) had a positive or questionable smear result, while chest radiography showed normal. The difference between patients with and without HIV was found to be small. Smoking status and having a good education were somewhat less likely to be associated with a subclinical course of TB.
"Most people with pulmonary TB do not report coughing. A quarter report no symptoms at all that would indicate the disease. However, a quarter of those without a cough have positive sputum smears, indicating that they are infectious. In settings of high incidence, subclinical tuberculosis may contribute significantly to the burden of the disease and increase the risks of mycobacterial transmission," the study authors concluded.