Difference Between Primary and Secondary Tuberculosis

Primary vs Secondary Tuberculosis

Tuberculosis or TB is caused by the bacterial group mycobacterium. It is mainly a respiratory tract infection, but can act as an opportunistic infection and a systemic infection in times of reduced or absent immunity. The causative bacterium is a bacillus and the culprit usually is mycobacterium tuberculosis. The infection is spread through respiratory droplets and sputum. About one third of the population of the world is thought to be infected, but most are asymptomatic, whilst some will present with a late infection and some showing with the initial infection, as well. The prevention of the brain and systemic infection is done through the BCG vaccine which confers protection. There are pharmaceuticals which are capable of killing this bacterium, and preventing the further spread. The use of these drugs needs to be carefully monitored and unnecessary use is discouraged due the incidence of multi drug resistant TB. In this article, we will discuss on the two main varieties of respiratory tuberculosis; namely the primary and secondary tuberculosis.

What is Primary Tuberculosis?

Primary TB is where the person is exposed to the bacilli, and then taken into the respiratory tract and ingested by macrophages, then either killed or lying dormant in the macrophage. There will be production of antibodies to the bacilli through a delayed type of hypersensitivity reaction. This immune response creates further activated cell and lymphocytes. All the while, the macrophages are taken into lymph nodes and retained there. The immune system creates a barricade around the lymph nodes with the bacilli in them. If for some reason, the immune system is not active enough, then an active primary TB occurs with the nocturnal fever with sweats, and chronic cough. If not overtime, the barricaded lymph nodes coalesce and retain calcium to form a Ghon focus.

What is Secondary Tuberculosis?

Secondary TB is where the patient gets the infection due to a previous exposure to the bacilli sometime back. The patient maybe a previously asymptomatic individual or had the infection and recovered. The immune system gets compromised due to another infection, drugs or immune compromise, leading to the breach in the immunological barricade around the dormant bacilli in the lungs. Here, the immunity against the bacteria has already being forged due to the past exposure. Because of this, the immune reaction against the bacteria can wreak havoc in the respiratory system leading to blood streaked purulent sputum with a chronic cough, loss of weight, and fever at night with night sweats, etc. If the immune system has not regained from the refractory immune suppression, then the symptoms like night sweats, fever and weight loss will be less, but the respiratory symptoms are greater.


What is the difference between Primary and Secondary Tuberculosis?

• Both primary and secondary TB occurs due to the bacilli, and they need to be exposed to that bacterium with a common mode of transmission.

• Both will give out common symptoms in accordance to their immune status, and management of both conditions is with the same regimen.

• Primary TB occurs with the exposure of the bacillus, and secondary TB after sometime from the exposure.

• Primary TB usually occurs when the immunity is normal, and secondary TB occurs when the immunity is faulty.

• Symptomatology is greater in secondary than in primary. Secondary TB can become extensive, whereas primary is localized.


  • Meena

    the TB which occurs in a person who is vaccinated ( BCG ) – is it primary or secondary?

  • yousif

    sure its , secondary