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EevaSalo

Exposure to Tuberculous Infection

Note: this article is based on the policy applied in Finland. See also your local official policy and guidance.

Risk of infection

  • Tuberculosis is an airborne infection. When a person with respiratory tuberculosis speaks or coughs, droplets spread in the air that dry and remain floating in the air. When another person breathes in the air, dried droplets get into their lungs.
  • The risk of infection is higher
    • the more bacteria the infection carrier's sputum contains,
    • the longer the two stay in the same room or share the same air space,
    • the smaller the room or shared air space and the poorer the ventilation.
  • People who shed enough bacteria in their sputum to be demonstrated by staining, or people with a cavity (cavern) found on chest x-ray are most contagious.

Definitions

  • To understand tuberculosis, it is important to differentiate between:
    • exposure to tuberculosis: the person has shared the same indoor air space as a person with contagious tuberculosis
    • tuberculosis infection: tuberculosis bacteria have entered the body, and have either been destroyed or remain latent there (latent tuberculosis, carrier state) and may later become active
    • tuberculosis (disease): the person has symptomatic disease caused by tuberculosis bacteria.

Risk of developing the disease

  • The risk of an infected person developing tuberculosis is greatest during the first two years. About 10% of all those infected fall ill.
  • Susceptibility to development of the disease depends on age. The risk is greatest in small children.
    • Every second infected infant less than one year of age develops active disease. These children often also develop dangerous, rapidly progressive forms of the disease.
    • The risk is lowest in children from 5 to 10 years of age but increases in puberty and young adults to 10 to 20%.

Contact tracing

  • Disease notification should be performed for every diagnosed case of tuberculosis.
  • Contact tracing should be performed whenever a case of contagious or possibly contagious tuberculosis, or a case of suspected newly acquired tuberculosis is diagnosed.

Infectious tuberculosis - who has been infected?

  • If infectious tuberculosis is diagnosed, contact tracing must be started, i.e. the people exposed to tuberculosis have to be traced. Contact tracing should be started and directed in specialized care by the doctor in charge of the patient.
  • Children below school age should be referred urgently (by phone or by written referral) from specialized care for assessment at a paediatric outpatient clinic.
  • Data on contacts should be submitted to the nurse and doctor responsible for infectious diseases at the primary health care centre, and the nurse and doctor should complete the list of exposed people with any further data they have obtained and organize further measures.

Children or adolescents with tuberculosis - finding the source of infection?

  • Tuberculosis in children or adolescents, as well as miliary tuberculosis or meningitis, are usually signs of recent infection. Contact tracing is needed to find the source of infection. People with infectious tuberculosis must be found and treated to avoid spreading the infection.

Examination of exposed persons

  • Exposed children under the age of 7 years should be examined and followed up at a paediatric outpatient clinic. The aim is to detect and treat the tuberculosis infection before the disease develops.
  • Exposed people with an underlying disease or medication increasing the risk of developing the disease should be referred directly to an outpatient clinic in specialized care (outpatient pulmonary or infectious diseases clinic or a clinic for treatment of the underlying disease) according to the locally agreed practice.
  • If the exposure is work-related, occupational health care should participate in the examinations.
  • In the case of mass exposure, examinations should be planned and performed in cooperation between specialized and primary health care.

Course of the examinations

  • Patients with symptoms should be identified quickly to prevent them from infecting further people with tuberculosis. Children below the age of 16 years with symptoms should be referred to a paediatric outpatient clinic; for adults, preliminary examinations should be performed in primary health care.
  • In primary health care, exposed school-aged children and adults should be sent a letter with a questionnaire, and a nurse will use the questionnaire to interview the person either by phone or in his/her office.
  • An IGRA test should be performed for 7-35-year-old patients 2 months after the last exposure. If the result is 1.0 IU/ml or more, a tuberculosis infection should be suspected. The doctor should write a referral to specialized care.
  • All those examined need to have a chest x-ray taken either at the time of the initial check-up or no later than 2 months after starting contact tracing.
  • If the person is asymptomatic and no tuberculosis infection is suspected based on IGRA testing or chest x-ray, follow-up should be stopped.
  • If IGRA testing has not been performed or no result can be obtained, chest x-ray and symptom inquiry should be repeated in 12 months (in the case of people 35 years old or older, only if they are close contacts).
  • At the initial check-up and follow-up visits, it is important to inform exposed people of the symptoms of tuberculosis and to instruct them to seek examinations without delay should such symptoms occur, even at a later date.
  • If the infectious strain is resistant to antitubercular agents, contact tracing should be carried out basically as described above. Persons exposed to tuberculosis should be followed for 2 years. Doctors responsible for follow-up should be informed about drug resistance.

Pregnant women

  • Pregnant women who have been exposed to tuberculosis should be examined like other exposed people. Symptomatic women should have a chest x-ray taken regardless of the phase of pregnancy, asymptomatic women during the last trimester, no later than 1 month before the due date.
  • If a woman giving birth is found to have infectious tuberculosis, the newborn baby must be isolated from his/her mother until PCR assay has shown that the mother is not suspected of having drug-resistant (MDR) tuberculosis. Preventive medication can in that case be started for the baby, who can then be given to the mother to nurse.

Children and BCG vaccination

  • BCG vaccination provides good protection against severe paediatric forms of the disease, miliary tuberculosis and meningitis, but clearly poorer protection against other forms of the disease.
  • In Finland, BCG vaccination is today offered only for risk groups Bcg Vaccine.
  • It is particularly important to begin examinations of unvaccinated children exposed to tuberculosis without delay, because their infection may rapidly spread to become miliary tuberculosis or meningitis.
  • Children living with patients with infectious tuberculosis and children who have been otherwise significantly exposed, who have the highest risk of developing the disease, should be put on preventive medication ("window prophylaxis") during which IGRA test conversion is monitored.
    • Children below the age of one year regardless of whether they have received BCG vaccination.
    • Children from 1 to 4 years who have not received BCG vaccination.
  • Preventive medication should be continued until at least 2 months from the last possible exposure. The IGRA test should be repeated in asymptomatic children. If it is negative, medication should be withdrawn. Unvaccinated children should be given BCG vaccination.
  • Small children do not usually transmit tuberculosis. Tuberculosis in a child is a result of a new infection. Look for the source of the infection, because this person poses a continuous threat to the environment if left untreated.

Treatment for latent tuberculosis infection (LTBI)

  • A person who has been infected with tuberculosis but has no symptoms and cannot be shown by tests to have signs of tuberculosis is considered to have a latent tuberculosis infection (LTBI).
  • Treatment of LTBI can reduce the risk of subsequent disease to about one tenth.
  • Treatment should be offered if a healthy person below the age of 35 is found to have a tuberculosis infection but not to have developed tuberculosis. Assessment of the need for treatment should be done in specialized care.
  • The need for the treatment of LTBI in patients with immunodeficiency who have been exposed to tuberculosis should be assessed in the unit treating the underlying disease.
  • In people over 35 years, the disadvantages of pharmacotherapy for LTBI usually exceed the advantages.
  • Alternatives for pharmacotherapy for LTBI:

Health care personnel

  • The staff risk of exposure to tuberculous infection may be especially high in connection with bronchoscopy, surgical procedures or autopsy of patients with unexpected tuberculosis.
  • In Finland, the risk of tuberculosis is lower among health care personnel than in the age-equivalent population on average.