Causes and Risk Factors of Tuberculosis

Approximately 1.7 billion people, 23 percent of the world's population, are infected with tuberculosis (TB). According to the World Health Organization, there were 10 million new cases and 1.6 million deaths from the disease in 2017 alone. The United States accounted for an estimated 7,500 of those new diagnoses in 2021.

While infection with bacteria is the definitive cause of TB, there are factors that can make you susceptible to the disease. Knowing what these factors are can help you to take action and decrease your risk of infection.

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Bacteria

Tuberculosis is caused by bacteria in the Mycobacterium complex family.

  • Mycobacterium africanum
  • Mycobacteria bovis
  • Mycobacterium tuberculosis

M. africanum, as the name implies, is most common in Africa, while M. tuberculosis is responsible for tuberculosis in most other parts of the world. These two bacteria cause the bulk of TB disease in humans. M. bovis is unique in that it mainly infects cattle. Drinking unpasteurized dairy products or other exposures to infected animals account for a small percentage of human tuberculosis cases.

Mycobacteria infect and live inside cells in the human immune system called macrophages. Macrophages normally kill microbes and pathogens, but M. tuberculosis has a thick waxy capsule that protects it against the toxic enzymes the macrophages use to attack it. TB is then able to reproduce inside the macrophage.

How TB Bacteria Spreads

There is a difference between latent and active TB infection.

Someone who has latent infection has TB bacteria in their body but does not have active disease. Without symptoms like fever, chills, coughing, and weight loss, they are not infectious, and the bacteria lie dormant in their body.

As many as 5 to 10% of people who have latent TB will go on to develop active TB in their lifetime. This most commonly happens within the first two years of the infection.

People who have active TB will experience symptoms of the condition. Active TB makes a person highly infectious. A person who has active TB can spread the disease when they cough, sneeze, spit, or talk, as tubercular bacteria is released into water droplets. Anyone who inhales these droplets could develop TB infection in the lungs.

In the United States, TB transmission is more common in the spring, with rates lowest in the fall.

Medical Factors

There are medical conditions that can increase your risk of developing tuberculosis.

Immunosuppression

A weakened immune system makes it harder for your body to fight infection and more likely that latent TB becomes active. It also makes it more likely to be infected with TB in the first place.

The following conditions can impair a person's immune system:

  • Age: The immune systems of the very young and the very old tend to be weak.
  • Chemotherapy: These treatments fight cancer but also weaken your immune system.
  • Corticosteroids: Anyone who takes oral steroids long-term, the equivalent of 15 mg prednisolone for a month or longer, has a weakened immune system.
  • HIV/AIDS: The risk of developing TB is estimated to be at least 16 times greater for people who also have HIV. As HIV disease worsens or progresses to AIDS, the risk for TB increases further.
  • Organ transplants: To prevent the body from rejecting a transplanted organ (heart, kidney, or liver), people typically take life-long immunosuppressant medications.
  • Tumor necrosis factor (TNF) inhibitors: These biologic medications are often used to treat medical conditions like Crohn's disease, psoriatic arthritis, and rheumatoid arthritis.

Chronic Medical Conditions

The following conditions could increase your risk for TB infection:

Some of these conditions impair the immune system or prevent adequate nutrient absorption. If you have one of these conditions, take steps to decrease your possible TB exposures.

Tuberculosis Doctor Discussion Guide

Get our printable guide for your next doctor's appointment to help you ask the right questions.

Doctor Discussion Guide Man

Lifestyle Factors

There are non-medical risk factors of TB that may be more within your control. Issues like poverty, homelessness, and decreased access to health care can make managing some of these factors challenging.

Diet and Nutrition

Poor nutrition plays a role in TB infection. Severe malnutrition weakens the immune system and leads to weight loss. People who are underweight (body mass index of <18.5) are twice as likely to be infected than people with a higher BMI.

When it comes to specific nutrients, iron and Vitamin D levels can have an impact:

  • High iron levels in the blood may promote the growth of mycobacteria, making people more susceptible to TB.
  • Vitamin D restricts the growth of mycobacteria, so a deficiency can increase your risk.

Vitamin D deficiency is a risk factor for tuberculosis.

Whenever possible, it is important to eat a nutrient-rich diet and maintain a healthy weight. Socioeconomic situations often make it challenging to do that.

Location

People born in areas where TB is endemic are at increased risk for exposure to the bacteria.

In 2017, eight countries accounted for two-thirds of the new TB cases:

  • India
  • Indonesia
  • China
  • Philippines
  • Pakistan
  • Nigeria
  • South Africa
  • Bangladesh

You may not be able to control where you are born but you can control where you go. At the very least, take precautions when you travel to these locations.

Living Conditions

TB can spread quickly when people are in crowded and poorly ventilated living and working environments. Crowded conditions within a community or even within a household increase that risk considerably. This is especially true when there is poor ventilation within a building.

If you rent an apartment or purchase a home, consider the safety of your living arrangement.

Homeless shelters, in particular, can be overcrowded and are not always properly maintained.

Substance Abuse

Substance abuse is prevalent among people infected with TB. Smoking cigarettes increases your risk as much as two-fold. Illicit drug use, whether injection or non-injection, and drinking 40 grams (one pint of wine, three 12-ounce beers, or 4 ounces of distilled liquor like vodka or whiskey) or more of alcohol per day also increase the odds of TB transmission.

It is in your best interest to avoid smoking and illicit drugs. If you drink alcohol, only do so in moderation.

Frequently Asked Questions

  • Can I be at risk for TB if I travel internationally?

    While some areas of the world have high rates of TB, the risk of acquiring it while traveling is very low, especially if you don’t visit areas with known TB outbreaks and avoid close contact with people who are ill. Be extra careful if you’re immunocompromised and talk to your doctor about being screened when you return.

  • Does tuberculosis increase your risk for COVID-19?

    Yes. Currently having TB and having a history of TB seem to make you more susceptible to COVID-19 and may increase your chances of a worse prognosis. There’s limited research on how the two diseases work together, though, and how other factors such as pre-existing diseases or obesity may affect you as well.

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10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading