TB Manual

4.3.1. Congregate settings and location-based screening

Screening of medium-priority contacts in schools, workplaces, hospitals, correctional facilities, shelters and other congregate settings is generally most efficiently and effectively carried out on site, especially if the number of identified contacts is large. However, it is critical to coordinate with site leadership and be very organized (see Appendix 2 for a recommended approach).

Unless the investigation is conducted in a systematic, risk-based manner, it may result in hundreds of “contacts” with limited or unknowable exposure and often dismal participation rates. There is often pressure to initiate widespread contact investigation from the outset (eg, to an entire school, including many low-priority contacts). If indiscriminate screening is performed with no accounting of exposure parameters, however, interpretation of results is extremely difficult. Unless the individual has a documented prior TST/IGRA result it is generally impossible to differentiate between a new versus remote infection in the context of a contact investigation. Contacts with minimal exposure may then be mistakenly identified as recently infected and the investigation expanded yet further.

Anxiety may be minimized by limiting the delay between contacting the site and conducting testing, ensuring that key people at the site get the same information at the same time and holding general education sessions about TB and the investigation plan. Communication from all personnel involved in the investigation should be clear, credible and consistent, especially about the actual level of risk involved and the clinical follow-up plan.

4.3.2. People affected by homelessness

Patients with TB who are homeless or underhoused may also suffer from alcoholism, drug addiction or mental illness, as well as other medical co-morbidities.^55,56 They often have poor access to health services, resulting in delayed TB diagnosis, worsening of the disease, prolonged infectiousness and thus large numbers of contacts who need to be assessed.^57–59 Many homeless shelters and rooming houses (single-room occupancy hotels) are crowded and have poor ventilation, making them high-risk settings for transmission. Where baseline prevalence rates of TST positivity are high, this also means that a large number of contacts will require further assessment and possible LTBI treatment.

Contact information can prove difficult to gather from individuals experiencing homelessness or severe addictions, related to recall, trust and competing priorities; contacts may be difficult to locate and have low participation rates for TB screening. These challenges can be made more manageable by recognizing that such patients are not “business as usual,” prioritizing efforts on risk and impact, ensuring person-centered care, collaborating with partners in the homeless/underhoused services sector and allocating adequate resources.⁶⁰ It is generally most productive to try to identify any particularly close friends or longer-term roommates by name, and to focus on location-based investigation for medium-priority contacts.^61–63 Homeless individuals may be highly mobile, with many locations exposed. Shelters may have bed logs, which can help to identify roommates; in large shared rooms, prioritize those who spent the most nights with the case and slept closest.^34,64 Also questions should be asked regarding time spent at drop-in centers or soup kitchens providing services for the homeless and underhoused (day-use shelters), libraries, bars, “party houses,” parks, and so forth. Staff at shelters or social service agencies and close friends or family may be able to identify daily patterns or specific close contacts. If there are gaps in the history during the infectious period, checking for recent hospitalizations or detainment in a correctional facility may identify additional exposures in these settings.

Homeless contacts may have significant challenges following through on TB screening, medical evaluation and treatment for LTBI.⁶⁵ TB programs should prioritize active case finding in order to curtail additional transmission in this high-risk group, and include LTBI screening if the program will be able to support counseling, follow-up and treatment for infected individuals. Non-judgmental and supportive TB staff, screening activities with the explicit goal of reducing barriers to participation and judicious use of incentives and enablers can help increase participation rates.^66,67 It may be possible to find “missing” contacts through confidential alert lists at key service providers so that if these individuals arrive, public health/TB program staff can connect with them for follow-up, though it is essential that partner agencies do not stigmatize these individuals.

Screening on-site at the exposure location and/or in a single session will usually have more success than arrangements involving extra visits or travel (eg, sputum collection or a portable chest x-ray machine at a shelter-based screening clinic; a one-stop-shop approach at a hospital TB clinic).^67–71 Similarly, IGRA may be preferable to TST for LTBI assessment if blood collection can be done on site. Both tests require individuals to be located twice if the goal is initiation of LTBI treatment, but the timeline for the second visit is not so constrained for IGRA as it is for reading a TST. Active participation and encouragement from trusted staff at the shelter or day program during screening clinics is especially helpful. Persistence and flexibility are critical; someone who is not willing to participate on one day may be willing another time.

4.3.3. Contacts during air travel and other transport

The risk of TB transmission during commercial airplane travel is low, and the value of actively screening airplane contacts is limited.⁷² Nevertheless, the WHO has published guidelines outlining the procedures for notifying contacts exposed on international flights with a total duration of ≥8 hours within the previous three months.⁷³ Notification of people with TB who report a history of air travel while infectious should be made to the Public Health Agency of Canada (PHAC) through the provincial/territorial TB program. The reporting form can be found at https://www.canada.ca/en/public-health/services/diseases/tuberculosis/health-professionals.html#a6.

The few published reports of contact tracing after exposure to TB on buses and trains indicate that transmission is possible on repeated daily exposure to the infectious individual, or on long-distance/multi-day trips.⁷⁴ Such events appear rare, and usually involve highly infectious patients and specific environmental circumstances (eg, daily school bus travel on a crowded, long-duration route in winter, with closed windows and recirculated air).⁷⁵ Taxi rides for local travel have not been associated with transmission.⁷⁶ There is no evidence to support contact tracing related to local public transportation, particularly given the logistic hurdles and considerable inefficiency of contact tracing in these circumstances.⁷⁷

4.3.4. Contact during residence or travel in a high-TB-incidence country

This is covered in Chapter 13: Tuberculosis Surveillance and Tuberculosis Infection Testing and Treatment in Migrants.