Exposure to Tuberculous Infection
Note: the policies and practices presented in this article are based on those applied in Finland. Therefore, some information may not apply in all settings. See also local policies and guidance.
Risk of infection
- Tuberculosis is an airborne infection. When a person with respiratory tuberculosis speaks or coughs, droplets containing tuberculosis bacilli are expelled and remain floating in the air. When another person breathes in the air, droplets get into their lungs.
- The probability of infection depends on the intensity and duration of the exposure and the exposed person's immunity.
- The risk of infection is higher
- the more bacteria the infection carrier's sputum contains,
- the closer the contact has been,
- 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 tuberculosis bacilli in their sputum to be demonstrated by staining, or people with a cavity (cavern) found on chest x-ray are most contagious.
- Small children do not usually transmit tuberculosis.
Definitions
- Exposure to tuberculosis: the person has shared the same indoor air space as a person with infectious tuberculosis
- Tuberculosis infection: tuberculosis bacteria have entered the body and caused a primary infection.
- Alternative courses: either the immune system destroys the infectious bacteria completely or the infection progresses directly to disease or remains latent (latent tuberculosis, carrier state) and may later proceed to active disease.
- Tuberculosis: the person has symptomatic disease caused by tuberculosis bacteria.
Risk of developing the disease
- Susceptibility to developing the disease after infection and to developing rapidly progressive forms of disease depends on age. The risk is greatest in small children. See Table T1.
- The risk of an infected person developing tuberculosis is greatest during the first two years after infection.
Risk of disease in relation to age at infection (*source 2)
| Age at infection* | Risk of disease | Risk of meningitis or generalized tuberculosis |
|---|
| < 1 yr | 50 % | 10-20 % |
| 1-2 yrs | 15-20 % | 2-5 % |
| 2-5 yrs | 5 % | 0.5 % |
| 5-10 yrs | 2 % | < 0.5 % |
| > 10 yrs | 10-20 % | < 0.5 % |
Contact tracing
- Disease notification should be performed for every diagnosed case of tuberculosis.
- Contact tracing should be performed whenever a case of infectious tuberculosis or of suspected newly acquired tuberculosis is diagnosed.
- See also local policies concerning contact tracing.
Infectious tuberculosis - who has been infected?
- If infectious tuberculosis is diagnosed, contact tracing must be started in specialized care by the doctor in charge of the patient.
- The aim is to trace people exposed to tuberculosis.
- Data on contacts should be submitted to the doctor responsible for infectious diseases in the area. Exposed children under the age of 7 years should be referred urgently (by phone or by written referral, depending on local policy) from specialized care for assessment at a paediatric outpatient clinic.
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.
- After finding the source of infection (index case), measures should be taken to prevent further infections and to trace other people who have been exposed to infection.
Examination of exposed persons
- The aim is to find among exposed people those who have been infected or who have developed the disease.
- Children under the age of 7 years should be examined at a paediatric outpatient clinic.
- 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 or from developing serious disease.
- Children below the age of 16 years with symptoms should be referred to a paediatric outpatient clinic;
- for adults, preliminary examinations can 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 also be performed for asymptomatic 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 in a person of 16 years or older, chest x-ray and symptom inquiry should be repeated in 12 months for people of 35 years old or older, only if they are close contacts). For children, consult a paediatrician (or a paediatric infectious diseases specialist).
- 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 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.
- Check local policy concering BCG vaccination in children. For differences in European countries, see http://vaccine-schedule.ecdc.europa.eu/Scheduler/ByDisease?SelectedDiseaseId=14&SelectedCountryIdByDisease=-1. See also BCG Vaccine.
- It is particularly important to begin examinations of unvaccinated small children exposed to tuberculosis without delay, because the infection may rapidly progress to become miliary tuberculosis or meningitis.
- Children living with patients with infectious tuberculosis and children who have been otherwise comparably 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.
- If the IGRA test remains negative in asymptomatic children, medication should be withdrawn and unvaccinated children below 7 years should be given BCG vaccination.
Treatment for latent tuberculosis infection (LTBI)
- When examinations show that a person is infected with tuberculosis but there are no signs of a disease, the person is considered to have a latent tuberculosis infection (LTBI).
- Treatment of LTBI can reduce the risk of subsequent disease to about one tenth.
- Assessment of the need for treatment should be done in specialized care. Treatment for LTBI is normally offered for healthy people below the age of 35.
- The need for the treatment of LTBI in immunocompromised patients should be assessed in the unit treating the underlying disease.
- In people over 35 years, the harms of pharmacotherapy for LTBI usually exceed the benefits.
- 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.
- However, for example in Finland, the risk of tuberculosis is lower among health care personnel than in the age-equivalent population on average. Find out about the local epidemiology.
References
- Marais BJ, Gie RP, Schaaf HS, et al. The natural history of childhood intra-thoracic tuberculosis: a critical review of literature from the pre-chemotherapy era. Int J Tuberc Lung Dis 2004;8(4):392-402 [PubMed]