Health Equity Blog
By Hyejeong Hong
The cure for multidrug-resistant tuberculosis (MDR-TB) is the same in the United States as it is in South Africa. Yet the drug regimen’s most severe and permanent potential side effect, hearing loss, occurs up to four times as often in South Africa. The reason is simple and stark: a lack of medical resources to identify those most at risk of this side effect.
Despite decades of effort to reduce mortality, TB and especially its modern, drug-resistant strain remain the leading cause of infectious disease-related deaths worldwide. We are dealing with a global health emergency. But there are things we can and must do to avoid causing unintended harm while we save the sick. Imagine no longer being able to hear your little daughter’s lovely voice or listen to your favorite song after TB treatment. You are alive, yes. But could your quality of life have been better protected? It appears yes.
MDR-TB is caused by bacteria resistant to classical TB drugs such as rifampicin and isoniazid. MDR-TB infection must be treated with synergistic combinations of second-line drugs: injectable aminoglycoside (AG) such as kanamycin and amikacin, along with four to five drugs taken orally. Unfortunately, MDR-TB treatment is prolonged (18-24 months), poorly-efficacious (only 50 percent treatment success), and poorly-tolerated.
Hearing loss as a reaction to AGs begins with an inability to process high-frequency (or high octaves like a woman’s or child’s voice) but can progress even with discontinuation of treatment. This can seriously impact patients’ lives after treatment. MDR-TB survivors may live with a disability that causes social isolation, threatens quality of life, and puts employment stability and family prosperity at risk.
The fact that there is a higher incidence of AG-induced hearing loss in South Africa than in the U.S. highlights the health inequities in treatment using AGs between countries. Although MDR-TB regimens in the U.S. also include AGs, only 13% of MDR-TB-infected patients suffer hearing loss versus 25% to 69% in South Africa. One of the reasons is that a lab test to monitor the AG concentration in the bloodstream—to assure non-toxic levels—is essential. In South Africa, however, such tests are not conducted due to financial constraints and lack of quality-assured labs. Despite the higher rates of devastating adverse effects in South Africa, AGs remain a mainstay of treatment because of their low cost and potent antibacterial activities, outperforming more expensive drugs with less severe side effects.
My questions regarding AG-induced hearing loss include: “Isn’t there any way to save both patients’ lives and their hearing together? What if the risk of AG-induced hearing loss can be estimated at initiation of MDR-TB treatment? Then health care providers could triage the high-risk patients to newer and less toxic drugs, such as Bedaquline, which, while more costly, will treat TB and eliminate such hearing loss!”
In South Africa, most TB programs offer Bedaquline as a substitute for AG only if a history or substantial risk of hearing loss is present at baseline. However, there is no practical and cost-effective means to identify those at highest risk for developing hearing loss. Today that risk is based solely on clinical expertise without a tested and validated measure to support those decisions. Such known risk of hearing loss led me to develop a mathematical tool to predict the probability of AG-induced hearing loss as a part of my dissertation project in South Africa.
To develop and apply this prediction tool, health care providers need to assess the level of health equity by measuring the individual’s socioeconomic level. The majority of TB-infected individuals in the country are black South Africans, HIV-coinfected, unemployed and/or social grant recipients due to disability or advanced age, and generally poor. Health inequity prior to TB treatment worsens the malnutrition and severity of MDR-TB and HIV progression, increasing the risk of AG-induced hearing loss. Thus, assessing the health inequity when predicting the risk of AG-induced hearing loss will support the health care providers’ clinical judgment to plan personalized treatment in those patients with higher probability where daily AG injection is required for MDR-TB. Such plans include, for example:
- Choosing Bedaquline.
- Adjusting drug dosage.
- Monitoring hearing more frequently.
- Adding nutritional supplements.
Policymakers can also use this prediction tool to develop successful reallocation of public health resources as follows:
- Distributing more Bedaquline and health care personnel for hearing tests.
- Providing free transportation to TB hospitals.
- Providing rehabilitation services, such as sign language education or hearing aids based on each patient’s socioeconomic positions within limited resources.
I expect that predicting hearing loss risk will reduce such unnecessary side effects in low-resource settings where drug concentration testing is infeasible. It will also reduce inequalities in health not only between groups of people within countries but between countries. If AG-induced hearing loss is predictable, it can be prevented, thereby reducing health disparities, achieving health equity, and improving quality of life as well.
Hyejeong Hong is a PhD candidate at the Johns Hopkins School of Nursing. She is actively involved in improving the health status and equity of people living with HIV/AIDS and tuberculosis in South Africa. Her dissertation focuses on developing a prediction model of drug-induced hearing loss in tuberculosis treatment in South Africa.