Certain factors determine whether or not a person will get infected with TB (Mycobacterium tuberculosis) when he or she is exposed to a TB-infected individual.
Some of the factors depend on the individual who is infected with TB and some depend on the person who is not infected with TB but is exposed to the TB-infected individual.
The factors include:
- Duration of exposure: This refers to the length of time for which the person was exposed to the bacteria, Mycobacterium tuberculosis. The longer the time spent with someone who is infected with TB, the higher the chances of becoming infected with TB.
- Size of the room: If an uninfected person stays in a small room or space with a TB-infected individual, there is a high risk of getting infected.
- The degree of air circulation and ventilation: Staying in a room that is not well ventilated (that is, does not have an adequate number of windows) with an infected person increases the risk of infection. Even if the windows are closed or less in number than is adequate and a fan is on, there is still a high risk of getting infected. This is because the air containing the TB bacteria is just being circulated and recirculated around the room. Good ventilation is important because it helps to reduce the concentration of the TB bacteria in one place which, in turn, reduces the chances of getting infected.
- Concentration of the bacteria (Mycobacterium tuberculosis): The higher the concentration of the TB-causing bacteria in the air, the more likely the chance of person(s) in that vicinity getting infected.
- State of the person’s immunity: Immune status is very important as it determines whether or not an individual will be defenceless against the infection. If an individual’s immune system is weak, then there is a high chance of becoming infected with TB if exposed to Mycobacterium tuberculosis. So, it is important to have a strong immune system.
Some of the things that can weaken the immune system are malnutrition (not eating enough food; eating too much junk food; excessively eating food high in salt, cholesterol, sugar, fat), being overweight or obese, too much stress and working too much, drinking alcohol, exercising excessively, chemotherapy, smoking, uncontrolled diabetes mellitus, organ transplant (because they are given drugs that weaken or suppress their immune system so as to reduce their chances of their body rejecting the transplanted organ), infections like HIV, being an intravenous drug user, using medications very often, to mention a few.
- Frequency of exposure: The number of times a person comes into contact with someone who has an active TB infection is also a key factor. The higher the number of times a person is around the TB-infected individual, the higher the risk of being infected with TB.
- How infectious the infected person is: This refers to the ability of a person who is infected with TB to infect others. And it is determined by the number of the TB-causing bacteria (Mycobacterium tuberculosis) that the infected person releases into the air. The higher the number of TB bacteria released into the air by the infected person, the higher the risk of the uninfected person(s) around getting infected. if the infected person coughs a lot and does not cover his/her mouth and nose when coughing, it increases the infectiousness of the individual with active TB disease. Also, if the person is not taking his/her medication in the appropriate manner as directed by the doctor, then this also increases the person’s infectiousness. So, not taking the drugs for the required length of time; or taking drugs that are not strong enough (not effective) against TB also allow the infected person to infect others.
- Proximity to the infected person: If you stay in close proximity to an individual who is infected with TB, there is an increased risk of being infected with TB.
- Improper handling of specimen: When a sample (for instance, a sputum sample) is collected from an infected person and handled carelessly, there is a high risk of infection occurring. This is because droplets containing the bacteria can be released into the air. The samples from someone who is suspected or confirmed to have TB should be handled carefully. And when it is being worked on, it should be inside a biological safety cabinet.
Not everyone who has TB is able to infect other people with the disease. An individual has to have an active TB disease to be able to spread the infection. People who are infected with TB but have a latent infection cannot infect others.