HomeWhile there are many publications regarding outbreak investigations and the outcome of contact tracing efforts arising from TB exposures in the healthcare setting, there is much variation in the exposure criteria used, the extent and duration of the investigation and the diagnostic tests used (see Appendix 1). Most contact investigations following healthcare-associated exposures find few secondary cases of either active or latent TB.10 Despite that, there is the expectation that health care organizations will undertake appropriate contact tracing and a need for relevant contact-tracing guidance in this setting.
Contact tracing following identification of a patient/resident with TB who has not been on airborne precautions or a HCW with TB who worked while infectious must be undertaken in an organized, systematic fashion and in close collaboration with local public health authorities.
Contact tracing principles and steps are described in Chapter 11: Tuberculosis Contact Investigation and Outbreak Management, including determination of infectiousness of the index case, likely period of infectiousness, degree of exposure and prioritization of contacts for screening and evaluation. Although the principles are the same in healthcare settings, there are some specific considerations.
Assessment of exposure: Exposure of HCWs or other patients is to be considered if they shared space with a patient with respiratory TB who was not on airborne precautions for any period of time during the infectious period. Exposure can also occur when an aerosol-generating medical procedure (e.g., high-pressure wound irrigation, procedure using power tools or cautery) is performed at or near the site of extra-pulmonary TB without airborne precautions.
Contact priority: In a typical contact investigation approach, contacts are classified as high-, medium- and low-risk priority, based on level of exposure and risk of progression to active disease.
In healthcare settings, the following are considered high-priority:
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Contacts equivalent to household members (e.g., roommate(s) in hospital or LTC home).
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Contacts anticipated to be at high risk of progression from latent TB infection to disease (e.g., aged less than 5 years, HIV infected, on dialysis, immune-compromised).
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Contacts exposed during aerosol-generating medical procedures without appropriate respiratory protection.
Initial investigation of contacts: In healthcare settings, it is typical to use somewhat lower thresholds for the initial contact investigation compared to the community, because of potential vulnerability of the patient population and risk for further transmission in the healthcare setting. However, it is still important to have a risk-based approach and not to include patients/residents and HCWs with minimal or no exposure whose risk of infection is negligible, and in whom screening could cause more harm than benefit.
The exact duration of exposure that defines a significant risk for acquiring TB is not defined. There is general agreement that any duration of exposure to an aerosol-generating medical procedure warrants contact tracing. Individual facility policies for contact tracing in healthcare settings have used exposure durations in non-aerosol-generating medical procedure situations that vary between two and 48 hours, modulated by the index case’s level of infectiousness, facility ventilation and the contact’s risk of developing active TB. In hospital settings, it may be useful to measure air change rates in the exposure areas, to help prioritize contacts. It is important to remember the need to expand an investigation to include a shorter cumulative duration of exposure if transmissions have been identified during the initial investigation. Outcomes for the investigation across all settings (healthcare and community) should be pooled to guide decisions around expanding the investigation. Table 3 provides a framework for establishing exposure thresholds for contact investigations in acute care settings, based on a range of exposure durations used by different jurisdictions. No evidence is available to recommend the use of a specific threshold.
Table 3. Suggested framework for TB transmission risk algorithm and contact follow-up. a
| Transmission Risk Factors | Transmission Risk Level | Criteria for Contacts | ||
|---|---|---|---|---|
| Patient with low risk of progression to active TB | Patient with high risk of progression to active TB | Staff | ||
| Aerosol-generating medical procedure | Very high | Not applicable | Not applicable | Any staff present without appropriate personal protective equipment |
| Laryngeal TB | Very high | 2-12 hours of cumulative exposure in shared air space | 2-3 hours of cumulative exposure in shared air space | ≥12 hours of cumulative exposure in shared air space |
| Smear-positive respiratory TB OR cavitation on chest x-ray |
High | 4-24 hours of cumulative exposure in shared air space | 2-12 hours of cumulative exposure in shared air space | 4-36 hours of cumulative exposure in shared air space |
| Smear-negative respiratory TB AND no cavitation on chest x-ray |
Low | 20-48 hours of cumulative exposure in shared air space | 4-24 hours of cumulative exposure in shared air space | 20-60 hours of cumulative exposure in shared air space |
Abbreviations: TB, tuberculosis .
a Framework adapted from St. Michael’s Hospital (Toronto) Exposure Investigation Guidelines for Patients & Staff Exposed to Pulmonary Tuberculosis (personal communication MP Muller) and Toronto Public Health’s Structured Risk-based Tool for Contact Investigations (see Chapter 11: Tuberculosis Contact Investigation and Outbreak Management). The framework was expanded to include range of exposure durations used by other jurisdictions.
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