Guide to the Application of Genotyping to Tuberculosis Prevention
and Control
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Applying Genotyping Results to Tuberculosis
Control Practices
Outbreak Investigations
Goals
The goals of an outbreak investigation are to identify and treat
all case-patients with active TB to stop transmission and to identify
all case-patients with LTBI that would benefit from treatment, and
assure that treatment is completed so the outbreak does not continue
in the future. Another goal of an outbreak investigation is to a)
understand the transmission dynamics that link TB patients and persons
with LTBI involved in the outbreak so that high-risk populations
can be identified and potentially targeted for future screening
efforts and b) expand our knowledge of how outbreaks occur.
Steps
An outbreak investigation has similar components to those of a
contact investigation with several important differences. One important
difference is the need to expand the scope of the identification
and evaluation of potential contacts. In many contact investigations,
the focus is on contacts that were named by the TB patient. In contrast,
in an outbreak investigation, the focus shifts to persons who spent
time at any location or social gathering identified by the TB patients.
Since this expanded universe of potential contacts often identifies
many more persons than can be evaluated with resources that are
usually available, an important step of an outbreak investigation
is to develop an algorithm that identifies the contacts who are
at highest risk of TB transmission and progression to TB disease
once infected. This involves defining the infectious period for
each TB case-patient, defining the exposed cohort of persons at
each location or gathering, determining the duration of exposure
to the case-patient, and using this information to prioritize the
various exposed cohorts for screening. For details about conducting
an outbreak investigation, see Appendix B, Core Steps in an Outbreak
Investigation.
In the previous discussion of the decision analysis depicted in
Figure 6.1, RFLP analysis was described only for patients who had
possible epidemiologic links. Most patients in an outbreak are connected
by known epidemiologic links, and an RFLP analysis of their isolates
usually will show a matching pattern. Nevertheless, it is usually
wise to perform an RFLP analysis on isolates from all patients involved
in an outbreak who have matching spoligotypes and MIRU types in
order to obtain additional confirmation of these suspected transmission
links.
Outcome
The expected outcome of an outbreak investigation is to stop transmission
of TB. This involves the rapid identification and treatment of all
infectious cases and the identification and treatment, if indicated,
of cases of LTBI. Evaluation of the success of an outbreak investigation
involves monitoring outbreak-related cases to verify the cessation
of treatment, or when additional cases are diagnosed, to ensure
they are rapidly detected and treated so they do not transmit TB
to others.
Last Reviewed: 05/18/2008
Content Source: Division of Tuberculosis Elimination
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
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