Defining a tuberculosis cluster or outbreak
DOI:
https://doi.org/10.33321/cdi.2016.40.37Abstract
Transmission of tuberculosis (TB) in an Australian context is a relatively uncommon event. However, episodes of transmission do occur, and may have a large significance in a low-incidence region. Defining when transmission has occurred is not straightforward in a variety of circumstances, but may have significant epidemiologic, public health and political implications. This paper, therefore, will review approaches to determining when transmission has occurred, and offer standardised Australian policy for classification of possible transmission events, including ‘clusters’ and ‘outbreaks’.
Key definitions:
A ‘cluster’ of TB cases will be any 2 or more active cases with identified epidemiological links and the same genotype of Mycobacterium tuberculosis as defined by the method used.
A ‘probable cluster’ will be any 2 or more active cases with identified epidemiological links where genotyping is not feasible (e.g. the case is not confirmed by culture) or the genetic variability between M. tuberculosis isolates recovered from cases is minimal, defined as no more than 1 locus variance for mycobacterial interspersed repetitive unit-variable number tandem repeat typing or as advised by expert analysis for whole genome sequencing.
A ‘possible cluster’ will be any 2 or more active cases with the same genotype as defined by the method used where temporal and geospatial association is plausible but no direct epidemiological link is identified.
An ‘outbreak’ will be defined as a cluster that includes 3 or more active cases with evidence of serial transmission.
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