Risk factor for tuberculosis

Tuberculosis facts

  • Tuberculosis (TB) is an infection, primarily in the lungs (a pneumonia), caused by bacteria called Mycobacterium tuberculosis. It is spread usually from person to person by breathing infected air during close contact.
  • TB can remain in an inactive (dormant) state for years without causing symptoms or spreading to other people.
  • When the immune system of a patient with dormant TB is weakened, the TB can become active (reactivate) and cause infection in the lungs or other parts of the body.
  • The risk factors for acquiring TB include close-contact situations, alcohol and IV drug abuse, and certain diseases (for example, diabetes, cancer, and HIV) and occupations (for example, health-care workers).
  • The most common symptoms and signs of TB are fatigue, fever, weight loss, coughing, hemoptysis, and night sweats.
  • The diagnosis of TB involves skin tests, chest X-rays, sputum analysis (smear and culture), and PCR tests to detect the genetic material of the causative bacteria.
  • Inactive tuberculosis may be treated with an antibiotic, isoniazid (INH), to prevent the TB infection from becoming active.
  • Active TB is treated, usually successfully, with INH in combination with one or more of several drugs, including rifampin (Rifadin), ethambutol (Myambutol), pyrazinamide, and streptomycin.
  • Drug-resistant TB is a serious, as yet unsolved, public-health problem, especially in Southeast Asia, the countries of the former Soviet Union, Africa, and in prison populations. Poor patient compliance, lack of detection of resistant strains, and unavailable therapy are key reasons for the development of drug-resistant TB.
  • The occurrence of HIV has been responsible for an increased frequency of tuberculosis. Control of HIV in the future, however, should substantially decrease the frequency of TB.

What is tuberculosis?

Tuberculosis (TB) is an infectious disease caused by bacteria whose scientific name is Mycobacterium tuberculosis. It was first isolated in 1882 by a German physician named Robert Koch who received the Nobel Prize for this discovery. TB most commonly affects the lungs but also can involve almost any organ of the body. Many years ago, this disease was referred to as “consumption” because without effective treatment, these patients often would waste away. Today, of course, tuberculosis usually can be treated successfully with antibiotics.

There is also a group of organisms referred to as atypical tuberculosis. These involve other types of bacteria that are in the Mycobacterium family. Often, these organisms do not cause disease and are referred to as “colonizers” because they simply live alongside other bacteria in our bodies without causing damage. At times, these bacteria can cause an infection that is sometimes clinically like typical tuberculosis. When these atypical mycobacteria cause infection, they are often very difficult to cure. Often, drug therapy for these organisms must be administered for one and a half to two years and requires multiple medications.

How does a person get TB?

A person can become infected with tuberculosis bacteria when he or she inhales minute particles of infected sputum from the air. The bacteria get into the air when someone who has a tuberculosis lung infection coughs, sneezes, shouts, or spits (which is common in some cultures). People who are nearby can then possibly breathe the bacteria into their lungs. You don’t get TB by just touching the clothes or shaking the hands of someone who is infected. Tuberculosis is spread (transmitted) primarily from person to person by breathing infected air during close contact.

There is a form of atypical tuberculosis, however, that is transmitted by drinking unpasteurized milk. Related bacteria, called Mycobacterium bovis, cause this form of TB. Previously, this type of bacteria was a major cause of TB in children, but it rarely causes TB now since most milk is pasteurized (undergoes a heating process that kills the bacteria).

Tuberculosis risk factors among tuberculosis patients in Kampala, Uganda: implications for tuberculosis control

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Discussion

A total of 520 patients participated in this case control study which was carried out in Addis Ababa, Ethiopia, which include 260 bacteriologically confirmed pulmonary TB patients and 260 clinic attendees. There is a high burden of Tuberculosis in many countries which may be attributed to its demographic and socio-economic profile like poverty, lack of knowledge, attitude and practice, overcrowding, malnutrition, co-morbidity, etc. Adequate information on epidemiological factors is essential in formulating national policy and to redirect health resources in order to control the transmission of TB as well as ensure better patient management. As no single factor is fully attributable for emergence of TB, and there is information gap on factors contributing to occurrence of TB, this study has tried to explore different socio-demographic factors. Ethiopia is among the 30 high burden countries for TB, TB/HIV as well as drug resistant TB that collectively contribute about 85–89% of the global burden .

The socio-demographic characteristics of the study participants indicated that 45.8% of cases and 46.2% of controls were in the 26–45 years age bracket, which is the most agile and economically active age group. This is similar to another study among TB patient in North Ethiopia, Gondar and Borumeda, which showed (54.9%) of the cases were within the age ranges of 26–45 years . Whereas other study at St Peter hospital, Addis Ababa, showed that 29.9% were in the age bracket 26–45 . Generally, the findings is consistent with other studies, which reported a rapid rise in TB morbidity and mortality among this young adult population mostly between 15–44 years of age . High risk of infection in this age group relates to having a higher number of social contacts in the community during young adulthood .

Majority of the cases (53.1%) have less than four family members, which is higher than the controls (44.6%). Overall household’s monthly income was reported to be lower for cases compared to controls, where 29.6% and 15.4% of cases and controls respectively live in household with less than 1000 Birrs per month. Other similar studies showed average monthly family income of upto 1000 birrs among 86.9% of participants in rural setting and 72.6% in urban area . Housing conditions were poorer for cases compared to controls, as higher percentage of cases (53.8%) live in single room house that controls (38.1%), whereas more controls (35.8%) than cases (22.7%) live in a two room house. Number of windows per house was also much lower for cases than controls, for instance 69.6% of cases and 55.8% of controls live in houses with single window or no window, while the figure is contrary to this when it comes to living in houses with multiple windows. In developing countries like Ethiopia most of the poor families face economic constrains, which leads to malnutrition, poverty, overcrowding, poor hygiene, decreased health care seeking attitude forming a vicious cycle of agent-host- environment increasing the risk for communicable diseases such as TB. Overcrowding has been previously documented as a strong risk for TB .

Almost fifth (18.1%) of the cases and 7.3% of controls had household members who had TB, which is close to findings of other study where 17.5% of TB patients reported family history of TB . Close contact is well described risk factor for TB . Close contact was estimated to account for 9–13% of the TB cases in Malawi . In a systematic review by Fox GJ et al. the prevalence of active TB and latent TB infection among TB contacts was 3.1% and 51.5% respectively . The effect of former experience of TB within the household has been observed consistently in other studies and such effect increased with the number of persons who had TB in the past . Furthermore, there was some evidence that this effect was higher when the former TB case was in close family link with the index TB case, as compared with unrelated household members. As reported in another study, within the households of TB case, the risk of TB infection increased with social proximity to the case, and that effect was persistently higher in first-degree than in more distant relatives .

Some (16.2%) of the cases and 6.5% of controls smoke cigarettes, and 40.5% of the cases smoke 6 to 10 cigarettes per day while 52.9% of controls do the same. The association between tobacco smoking and TB is well described in other studies . The prevalence reported in this study does not differ significantly from those reported in other studies in Africa but differs from those in other continents . Such differences could be attributed to background smoking prevalence in the general population.

This study also investigated alcohol use among TB patients and controls. About a third (33.5%) of cases and 30.8% of controls reported alcohol consumption, of whom 36.2% drink rarely, majority of both groups do it rarely. The prevalence of alcohol consumption in this study is lower than the result of national survey conducted in the general population where 35% of women and about half of men (46%) reported drinking alcohol . Practically there is no major difference in alcohol consumption among cases and controls.

Almost three fourth of both cases and controls had history of visiting a health facility during the 12 months before diagnosis of current illness. History of hospital admission was more than double among cases compared to controls. Chronic illness such as diabetes mellitus reduce the competency of the immune system, pulmonary diseases minimize function of the cilia and removal of inhaled substances, and hence increases risk of TB. Besides, people with chronic illness visit health facilities frequently and have increased risk of acquiring TB.

According to the multivariable logistic regression analysis, seven variables were found to be independent predictors for the occurrence of TB after controlling possible confounders.

Those subjects who live in house with no window or one window were almost two times more likely to develop TB compared to people whose house has multiple windows (AOR = 1.81; 95% CI:1.06, 3.07). Inadequate ventilation and overcrowding has been documented as a risk factor for TB from several other studies in a variety of settings . People who live in house without any window or single window at high risk of TB as it compromises ventilation and increase risk of transmission of airborne infection such as TB. Besides, they might be among the lowest income groups in the society, and if have bigger family size, that leads to overcrowding and malnutrition which will further increase the risk. This hence increase vulnerability to contagious diseases, and that creates favourable environment for TB transmission.

Patients who had previous history of hospital admission were more than three times more likely to develop TB compared to those who had no previous history of hospital admission (AOR = 3.39; 95% CI: 1.64–7.03). This indicates that visiting health facilities has risk of acquiring TB, demonstrating the need to establish a strong system for infection control in health care settings. A longitudinal study conducted in Western Ethiopia revealed that the incidence rate of hospital acquired infection was 28.15 per 1000 patient days while the overall prevalence was 19.41% (95% C.I: (16.97–21.85), and pneumonia and other respiratory tract infections were among the top ten diseases . Similarly another study in Northern Ethiopia showed a mean prevalence of hospital acquired infection of 14.9% (95% confidence interval 12.7–17.1), Pneumonia and respiratory tract infection being the second commonest with prevalence of 18.5% (95% confidence interval of 11.9–25.9) . Therefore, transmission of infection in hospital setting is common in Ethiopia and people who have history of admission have high chance of acquiring infection during their stay in the ward. The risk is higher among people who had longer duration of admission and among those with repeated admission.

Smoking has also been identified as important risk factor for developing TB by four times (AOR = 4.43; 95% CI: 2.10, 9.3). This was well established fact in several studies, for instance, AOR = 3.90; 95% CI = 1.20–12.40) , OR = 2.12, 95% CI 1.20–3.74) and statistically significant effects . Smoking results in histological changes in the lower respiratory tract, including peri-bronchial inflammation, fibrosis, vascular intimal thickening, and destruction of alveoli. This leads to alterations in the epithelial function, such as reduced ciliary activity, decreased clearance of inhaled substances, and abnormal vascular and epithelial permeability, and in effect increasing the risk of developing pulmonary diseases such as TB. However the prevalence of smoking in this study is so low to explain any possible association.

BCG was found to be protective against TB reducing the risk by one-third (AOR = 0.34; 95% CI: 0.22, 0.54). This has be documented in other studies, where absence of BCG vaccination, as significant risk factors for LTBI and that could facilitate disease transmission . Those with BCG vaccination were less likely to have occupationally-acquired PTB than those without vaccination (OR = 0.86, 95% CI = 0.20–3.6 .

We acknowledge possibilities for residual confounders in this study. Those with high household income are likely to live in houses with multiple windows, better awareness about prevention and control, better access to health service, BCG vaccination, etc. A big scale researches with adequate sample size and sufficient representation of the diverse variables can help to filter out the relative effect of each factor.

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TB Risk Factors

Some people develop TB disease soon after becoming infected (within weeks) before their immune system can fight the TB bacteria. Other people may get sick years later, when their immune system becomes weak for another reason.

Overall, about 5 to 10% of infected persons who do not receive treatment for latent TB infection will develop TB disease at some time in their lives. For persons whose immune systems are weak, especially those with HIV infection, the risk of developing TB disease is much higher than for persons with normal immune systems.

Generally, persons at high risk for developing TB disease fall into two categories:

  • Persons who have been recently infected with TB bacteria
  • Persons with medical conditions that weaken the immune system

Persons who have been Recently Infected with TB Bacteria

This includes:

  • Close contacts of a person with infectious TB disease
  • Persons who have immigrated from areas of the world with high rates of TB
  • Children less than 5 years of age who have a positive TB test
  • Groups with high rates of TB transmission, such as homeless persons, injection drug users, and persons with HIV infection
  • Persons who work or reside with people who are at high risk for TB in facilities or institutions such as hospitals, homeless shelters, correctional facilities, nursing homes, and residential homes for those with HIV

Persons with Medical Conditions that Weaken the Immune System

Babies and young children often have weak immune systems. Other people can have weak immune systems, too, especially people with any of these conditions:

  • HIV infection (the virus that causes AIDS)
  • Substance abuse
  • Silicosis
  • Diabetes mellitus
  • Severe kidney disease
  • Low body weight
  • Organ transplants
  • Head and neck cancer
  • Medical treatments such as corticosteroids or organ transplant
  • Specialized treatment for rheumatoid arthritis or Crohn’s disease

Related Links

For Patients

  • TB – General Information (Fact sheet)
  • Questions and Answers About TB (Booklet)
  • You Can Prevent TB (Fact sheet)
  • State TB Control Offices

For Health Care Providers

  • Targeted Tuberculin Testing and Interpreting Tuberculin Skin Test Results (Fact sheet)
  • The Difference Between Latent TB Infection and TB Disease (Fact sheet)
  • TB Guidelines

Tuberculosis: Risk Factors, Causes, and Prevention

Tuberculosis can be prevented by knowing how the infection spreads and what puts someone at a higher risk for the disease.

The bacteria that cause tuberculosis, Mycobacterium tuberculosis, are spread from person to person when someone with TB disease releases the bacteria into the air by coughing, sneezing, talking, or singing.

Mycobacterium tuberculosis is spread from person to person when someone with an active form of tuberculosis (TB) emits tiny, bacteria-containing droplets into the air through coughing, sneezing, talking, singing, or laughing. The bacteria can remain suspended in the air for hours, potentially infecting anyone who breathes them in. (1,2)

When a patient who has never been exposed to TB inhales the bacteria, it results in an initial TB infection, or primary infection. At this stage, some people have no symptoms, while others may experience fever or pulmonary symptoms.

In most people who’ve inhaled the bacteria, the immune system immediately kicks in and you recover without further signs of the disease. Or the bacteria may then remain in a latent, or dormant, state — it’s in your system, but not making you sick. But in some cases, the bacteria eventually reactivate and multiply, leading to the active form of TB — when it makes the person symptomatic and contagious. (3)

Latent TB shouldn’t be ignored, though, because the disease can become active at any time if your immune system gets weakened. According to the Centers for Disease Control and Prevention (CDC), about 5 to 10 percent of people infected with latent TB develop active TB at some point in their lives if they don’t receive treatment. (4)

Each stage doesn’t necessarily have to lead to the next, according to Asim A. Jani, MD, a hospital epidemiologist based in Orlando, Florida.

“This results in at least three levels of prevention,” he says.

  1. Avoiding initial exposure to places and people at high risk of having TB helps to prevent TB infection.
  2. Giving specific prophylactic TB medication to people who have been exposed and are also infected with latent TB can reduce the roughly 10 percent lifetime risk of developing the actual disease to less than 1 percent.
  3. Treating the active disease not only helps the person affected, but also helps prevent transmission to others.

What Are the Risk Factors for Getting Tuberculosis?

Risk factors for tuberculosis include anything that weakens a person’s immune system or puts someone in frequent, close contact with a person who has active TB. (1,4,5,6)

In the United States, you’re more likely to get TB if you travel to or have emigrated from a country with high rates of tuberculosis. Certain populations are at a higher risk because their immune systems are weaker.

More than 95 percent of TB deaths happen in low and middle-income countries, according to the World Health Organization (WHO). Areas of the world with higher rates of tuberculosis include: (1,7)

  • Africa
  • Asia
  • Eastern Europe
  • Russia
  • Latin America
  • Caribbean Islands

These eight countries made up two-thirds of new TB cases in 2017: (7)

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

Robert Amler, MD, dean of the School of Health Sciences and Practice and vice president for government affairs at New York Medical College in Valhalla, New York, recommends visiting the CDC’s Traveler’s Health website for updates on tuberculosis and other infectious diseases before you travel abroad.

Some of the main risk factors for tuberculosis include: (1,4,5,6,8)

  • Poverty People living in poverty often lack access to quality healthcare. It’s also possible that in the United States, people with little means could be living close to those who have recently emigrated from a country where TB is common. (1)
  • HIV Infection Because HIV attacks the immune system, it puts people at greater risk of getting sick from other bacteria and viruses. The combination of HIV and TB can be especially deadly because the two diseases feed off each other. In 2017, about 300,000 people with HIV died of TB, worldwide. (7)
  • Homelessness People who are homeless often live in crowded conditions with little or no access to healthcare.
  • Being in Jail or Prison Incarcerated people are often in enclosed areas with a crowd, breathing the same air.
  • Substance Abuse Intravenous (IV) drug use and alcoholism weaken the immune system.
  • Taking Medication That Weakens the Immune System Autoimmune disorders, like rheumatoid arthritis, psoriasis, and Crohn’s disease, cause the body’s immune system to attack itself. Treatments for these disorders often involve medication that suppresses the immune system. But that means your immune system may not be able to fight off TB after exposure. (6)
  • Kidney Disease and Diabetes Chronic conditions, like kidney disease and diabetes, weaken your immune system, making it harder for the body to fight of TB.
  • Organ Transplants The drugs people take to prevent the rejection of an organ transplant can weaken the immune system.
  • Working in Healthcare Doctors, nurses, and other healthcare workers get exposed to lots of patients on a regular basis, which means they’re also more likely to be close to someone with tuberculosis.
  • Cancer Chemotherapy weakens the immune system.
  • Smoking Tobacco Smoking can increase your risk of getting TB and dying from it. The WHO estimates 8 percent of TB cases worldwide can be linked to smoking. (1,7)
  • Babies, Young Children, and Elderly People The immune system can be more vulnerable when someone is very young or very old.

How to Prevent the Spread of Tuberculosis

In general, the best way to prevent tuberculosis is to keep your immune system healthy and avoid getting exposed to someone with active TB.

Throughout history, general improvements in health and hygiene have shown drastic reductions in TB cases, says Hayan Yacoub, MD, internal medicine practitioner at Austin Regional Clinic in Texas. Dr. Yacoub has treated people with latent TB at his practice. As a safeguard against TB, he recommends eating healthy and exercising to keep your immune system strong.

“Not everyone ends up with TB or latent TB because your immune system can fight it off,” says Yacoub.

Another big part of preventing new tuberculosis cases is identifying and treating people with latent TB before the disease can become active, especially in high-risk populations. If latent TB is treated properly, the bacteria can be killed before it multiplies, making the person sick and infectious.

To prevent the transmission of tuberculosis in healthcare settings, the CDC has issued guidelines that require most employees to be screened for tuberculosis when they’re hired and then again on a regular, often annual, basis. The testing frequency will depend on the worker’s likelihood of being exposed to TB. (9)

Some residential institutions, such as nursing homes, also screen all new residents for tuberculosis.

Screening for active TB is best accomplished by a chest X-ray.

Some other steps toward preventing the spread of TB include:

  • Improving ventilation in indoor spaces so there are fewer bacteria in the air
  • Using germicidal ultraviolet lamps to kill airborne bacteria in buildings where people at high risk of tuberculosis live or congregate
  • Treating latent infection before it becomes active
  • Using directly observed therapy (DOT), in which people taking medication for TB are monitored by their healthcare providers, to raise the likelihood of successful treatment

Long flights, like those lasting 8 hours or more, give you more time to breathe in infectious material from other people’s lungs, says Dr. Amler. If you’re traveling to parts of the world where there are a lot of crowded, enclosed environments, Amler suggests talking to your doctor about screenings when you return.

How Effective Is the Tuberculosis Vaccine?

A vaccine for tuberculosis called bacille Calmette-Guérin, or BCG, has been around since the 1920s. It was created from a weaker strain of the Mycobacterium bovis bacteria, a version of tuberculosis that affects cows. It’s used in parts of the world with high rates of the infection to prevent serious complications, like meningitis, which is common in young children. (10,11)

But BCG is rarely used in the United States because some studies have shown that BCG is not very effective in preventing TB cases, and because treatment of latent TB infection with isoniazid is a more effective prevention strategy. (10)

People who might benefit from BCG are children or healthcare workers constantly being exposed to others with an active infection. Typically, doctors would only recommend a child get the vaccine if they live with an adult who has active TB and are unable to take the antibiotics needed to treat TB, or if the adult has a strain of TB that’s resistant to antibiotics. (10,11)

At-Risk Populations for Tuberculosis

People at high risk for Tuberculosis (TB) exposure and infection include:

  • Close contacts of persons exposed to contagious cases of TB
  • Foreign-born persons, including children, who have immigrated within the last 5 years from areas that have a high TB incidence
  • Residents and employees of high-risk congregate settings (prisons, nursing homes, homeless shelters, drug treatment facilities, and healthcare facilities)
  • Healthcare workers who serve high-risk clients
  • Some medically under served, low-income populations as defined locally
  • High-risk racial or ethnic minority populations defined locally as having an increased prevalence of TB
  • Infants, children, and adolescents exposed to adults in high-risk categories
  • Persons who inject illicit drugs or any other locally identified high-risk substance users

People at high risk for progression to TB disease once infected include:

  • Persons with human immunodeficiency virus HIV infection
  • Persons who were infected with M. tuberculosis within the past 2 years, particularly infants and very young children
  • Persons who have underlying medical conditions known to increase the risk of progression to active disease
  • Persons who inject illicit drugs
  • Persons with a past history of inadequately treated TB

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