TB Manual

Recommended priorities for initial contact investigation are outlined below. These are guidelines: it is always important to consider the specific circumstances, work from first principles of TB transmission and re-evaluate according to the results of the investigation as they become available. See Appendix 1 for an example of a structured, risk-based tool to guide initial contact investigation.

Contacts can be prioritized according to high, medium and low priority:

• High-priority contacts are those with the most exposure, and those with the highest risk of progression to active TB if infected. They can include:

  • household contacts, who regularly sleep in the same household as the infectious case on an ongoing basis (eg, 3 or more times per week) and can include members of an extended family, roommates, boarders, couch-surfers, etc.;

  • household-like contacts in congregate settings, such as homeless shelters, jails and long-term care facilities (generally, room-mates or cell-mates);

  • caregivers with extensive/daily exposure to the index patient;

  • contacts exposed (ie, without an N95 mask) during bronchoscopy, sputum induction, autopsy or other aerosolizing medical procedures (see Chapter 14: Prevention and Control of Tuberculosis Transmission in Healthcare Settings; and

  • medium-priority contacts who are at high risk of progression of LTBI to TB disease (eg, aged less than 5 years, HIV, dialysis, transplant, silicosis (see Chapter 4: Diagnosis of Tuberculosis Infection).

• Medium-priority contacts have regular contact with the index case and share air space at least several times weekly but do not sleep in the same household most of the time. Most social, school and workplace close non-household contacts fall into this group, which may include:

  • caregivers with less extensive exposure to the case;

  • regular sexual partners;

  • close friends;

  • extended family;

  • daycare and primary/secondary school classroom contacts;

  • coworkers who work in close proximity, particularly in small rooms;

  • homeless/underhoused individuals using the same drop-in program regularly; and

  • low-priority contacts who are at high risk of progression of LTBI to TB disease, (eg, aged less than 5 years, HIV, dialysis, transplant, silicosis (see Chapter 4: Diagnosis of Tuberculosis Infection).

• Low-priority contacts are casual contacts who spend time regularly but less frequently with the infectious case. Investigation should be expanded to this group only if there is significant evidence of transmission among closer contacts. This group may include:

  • high school students who share only one course with the TB patient;

  • classmates in very large college/university classes;

  • less exposed colleagues at work;

  • members of a club, team or other social/recreational/religious group; and,

  • extended family members who are seen occasionally.

As shown in Figure 3, for index patients who are smear-positive or have cavitary disease, the initial group of contacts to investigate should include both high- and medium-priority contacts. For smear-negative index patients, initial contact investigation should include high-priority contacts only; investigation should be expanded to medium-priority contacts only if there is evidence of transmission among the closer contacts.

The specific circumstances should always be considered (see the Risk Assessment section). For example, a choir group meeting once per week to sing close together indoors may pose significant risk⁵³ but a regular outdoor soccer game generally poses little risk.

Expansion of the investigation to low-priority contacts should be only undertaken if there is clear evidence of transmission in the initial investigation, moving in a concentric circle model to the group with next-closest contact (see the section on Expanding Contact Investigation).

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