The World Health Organisation 2022 Global Tuberculosis (TB) Report report indicates an increase in TB deaths and infections in 2021 compared to 2020 — about 10.6 million people fell ill with TB in 2021 and another 1.6 million people died from the disease (including 187,000 among HIV positive people) worldwide. The report is a wake-up call to everyone.
The burden of drug-resistant TB also increased for the first time in many years by 3 per cent between this period, with 450,000 new cases of TB resistant to rifampicin, a key first line drug. These increments coincided with the Covid-19 pandemic.
About one-quarter of the world—approximately 2 billion persons—is infected with the bacteria causing TB (also known as latent TB), but only 5 to 10 per cent of these will develop active TB disease during their lifetime. Before the novel coronavirus, TB was the leading cause of death from a single infectious agent.
While there is TB in every part of the world, 30 high-TB burden countries, including Kenya, account for 86 per cent of new cases every year. India leads the count with roughly one-quarter of the world’s TB cases.
TB is curable—about 85 per cent of people who develop TB can be successfully treated with a six-month drug regimen. It’s also preventable. For example, in 1900, 194 out of every 100,000 US residents died from TB but, by 1940, before the introduction of antibiotic therapy/streptomycin, the crude death rate had decreased to 46 per 100,000 persons. In 2020, the TB death rate in Kenya and the USA was 39 and 0.2 cases per 100,000 people respectively, according to World Data Atlas.
Although anyone among the 2 billion persons worldwide infected with latent TB bacteria can develop active TB disease, six risk factors account for most of the new TB cases. These are HIV infection (19 per cent); malnutrition (27 per cent); those exposed to indoor air pollution (26 per cent); alcohol use disorder (13 per cent); diabetics (6 per cent) and active smokers (23 per cent).
In HIV endemic countries such as Kenya and South Africa, the population attributable risk fraction for TB attributable to HIV infection is as high as 50 per cent, meaning that simply preventing new HIV infections and addressing malnutrition could drastically reduce the new TB infections by 75 per cent. In India, China, Russia and Baltic states where HIV prevalence is low, new TB cases are mostly attributed to smoking tobacco and type 2 diabetes.
TB can be controlled using biomedical interventions, also known as disease prevention, and by preventing new infections from occurring. Unfortunately, most TB control programmes focus more on disease prevention—isoniazid preventive therapy, intensified case finding, rapid diagnosis, drug sensitivity testing to drive treatment and early access to ART—at the expense of infection prevention.
TB infection control comprises of administrative controls such as separating coughing patients in hospital waiting areas and fast-tracking their consultations; environmental controls such as natural and mechanical ventilation to ensure at least six to 12 air exchanges per hour; and using personal protective equipment such as masks.
TB bacteria—as well as the novel coronavirus, chickenpox and measles virus—spreads through tiny droplets in the air known as aerosols when an infected person coughs, talks, breathes, sings or sneezes. Because the bacteria is airborne, it easily attacks groups of tightly connected people in close contact and in poorly ventilated spaces such as public transport, prisons, hospitals, schools, congested housing, offices, dormitories, bars and places of worship.
Being lighter, the tiny aerosols can linger in the air for much longer even after the infectious person has left the room. In a crowded, poorly-ventilated indoor spaces, a single person infected with active tuberculosis can release enough particles in the air over time to infect many people and seeding a super-spreader event. Opening windows to increase indoor air circulation is a simple strategy to reduce transmissions.
Once a person is infected with one TB strain, it doesn’t mean that they cannot be re-infected with a different one. Molecular epidemiological studies have proved that one can be infected with multiple TB strains, including those resistant to TB drugs, eventually increasing one’s risk of developing active disease.
A ground-breaking 2006 South African Lancet study by Dr Ned Gandhi identified multiple TB drug-resistant strains as the main cause of rapid deaths in patients co-infected with TB and HIV. It costs a minimum of $2,000 to treat one patient with drug resistant TB and patients must take medications for at least nine to 20 months.
Healthcare workers are most at risk of getting infected with drug-resistant and drug-susceptible TB bacteria if they don’t wear masks when attending to sick patients and studies estimate that 54 per cent of health workers worldwide have latent TB infection.
The WHO defines TB exposure as contact between persons in sufficient proximity to hold a conversation or within confined, poorly-ventilated spaces. Wearing N95 respirator and surgical masks can drastically reduce the risk of TB transmissions in such settings. One study in South Africa where all patients waiting to be seen in hospitals were required to wear surgical masks showed a remarkable 59 per cent reduction in transmission of drug-resistant TB strains.